CoRE                                                           Z. Shelby
Internet-Draft                                                       ARM
Intended status: Informational                                   M. Vial
Expires: January 7, April 21, 2016                               Schneider-Electric
                                                               M. Koster
                                                                     ARM
                                                            July 6,
                                                        October 19, 2015

                            CoRE Interfaces
                     draft-ietf-core-interfaces-03

  Reusable Interface Definitions for Constrained RESTful Environments
                     draft-ietf-core-interfaces-04

Abstract

   This document defines well-known a set of reusable REST interface descriptions for
   Batch, Sensor, Parameter and Actuator types resource design patterns
   suitable for use in contrained web
   servers using the constrained environments, based on IETF CoRE Link Format.  A short reference is provided
   standards for each type that can be efficiently included in information representation and information exchange.

   Interface types for Sensors, Actuators, Parameters, and resource
   Collections are defined using the interface
   description "if" link attribute of the defined by CoRE
   Link Format.  These descriptions
   are intended to be for general Format [RFC6690].  Clients may use in resource designs or for
   inclusion in more specific interface profiles.  In addition, this
   document defines the concepts of Function Set and Binding.  The
   former is the basis element "if" attribute to create RESTful profiles and the latter
   helps the configuration
   determine how to consume resources.

   Dynamic linking of links state updates between resources located resources, either on one an
   endpoint or
   more endpoints. between endpoints, is defined with the concept of Link
   Bindings.  We also define conditional observation attributes that
   work with Link Bindings or with simple CoAP Observe [RFC7641].

Status of this This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 7, April 21, 2016.

Internet-DrafReusable Interface Definitions for Constrained October 2015

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .  3   4
   3.  Function Set  Interface Types . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Collections . . .  4
     3.1.  Defining a Function Set . . . . . . . . . . . . . . . . .  4
       3.1.1.  Path template . . . . .   5
     4.1.  Introduction to Collections . . . . . . . . . . . . . . .   5
       3.1.2.  Resource Type
     4.2.  Use Cases for Collections . . . . . . . . . . . . . . . .   6
     4.3.  Content-Formats for Collections . . . .  5
       3.1.3.  Interface Description . . . . . . . . .   7
     4.4.  Links and Items in Collections  . . . . . . .  5
       3.1.4.  Data type . . . . . .   7
     4.5.  Queries on Collections  . . . . . . . . . . . . . . . .  6
     3.2.  Discovery .   9
     4.6.  Observing Collections . . . . . . . . . . . . . . . . . .   9
     4.7.  Hypermedia Controls on Collections  . . . . .  6
     3.3.  Versioning . . . . . .   9
     4.8.  Collection Types  . . . . . . . . . . . . . . . . . .  6
   4.  Bindings . .  10
     4.9.  The collection+senml+json Content-Format  . . . . . . . .  10
   5.  Link Bindings and Observe Attributes  . . . . . . . . . . . .  11
     5.1.  Format  . . . . .  6
     4.1.  Format . . . . . . . . . . . . . . . . . . . .  12
     5.2.  Binding methods . . . . . .  7
     4.2.  Binding methods . . . . . . . . . . . . . . .  13
     5.3.  Binding table . . . . . .  8
     4.3.  Binding table . . . . . . . . . . . . . . . .  14
     5.4.  Resource Observation Attributes . . . . . .  9
   5. . . . . . . .  14
   6.  Interface Descriptions  . . . . . . . . . . . . . . . . . . . . 10
     5.1.  15
     6.1.  Link List . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.2.  17
     6.2.  Batch . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.3.  17
     6.3.  Linked Batch  . . . . . . . . . . . . . . . . . . . . . .  18
     6.4.  Hypermedia Collection . . 12
     5.4.  Sensor . . . . . . . . . . . . . . . .  19
     6.5.  Sensor  . . . . . . . . . . 13
     5.5. . . . . . . . . . . . . . . .  20
     6.6.  Parameter . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.6.  21
     6.7.  Read-only Parameter . . . . . . . . . . . . . . . . . . . 14
     5.7.  21
     6.8.  Actuator  . . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.8.  21
     6.9.  Binding . . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.9.  Resource Observation Attributes  22
     6.10. Future Interfaces . . . . . . . . . . . . . 16
     5.10. Future Interfaces . . . . . . .  23
     6.11. WADL Description  . . . . . . . . . . . . . 17
     5.11. WADL . . . . . . .  23
   7.  Function Sets and Profiles  . . . . . . . . . . . . . . . . .  29

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     7.1.  Defining a Function Set . . . . . . . . . . . . . . . . .  29
       7.1.1.  Path template . . . . . . . . . . . . . . . . . . . .  30
       7.1.2.  Resource Type . . . . . . . . . . . . . . . . . . . .  30
       7.1.3.  Interface Description . . . . . . . . . . . . . . . .  30
       7.1.4.  Data type . . . . . 17
   6. . . . . . . . . . . . . . . . . .  31
     7.2.  Discovery . . . . . . . . . . . . . . . . . . . . . . . .  31
     7.3.  Versioning  . . . . . . . . . . . . . . . . . . . . . . .  31
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . 23
   7.  31
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
   8.  32
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
   9.  32
   11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 23
   10.  32
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     10.1.  34
     12.1.  Normative References . . . . . . . . . . . . . . . . . . . 25
     10.2.  34
     12.2.  Informative References . . . . . . . . . . . . . . . . . . 25  34
   Appendix A.  Profile example  . . . . . . . . . . . . . . . . . . . 25  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 26  36

1.  Introduction

   The Constrained RESTful Environments (CoRE) working group aims at
   realizing the REST architecture in a suitable form

   IETF Standards for the most machine to machine communication in constrained nodes (e.g. 8-bit microcontrollers with limited RAM and
   ROM)
   environments describe a REST protocol and networks (e.g. 6LoWPAN).  CoRE is aimed at machine-to- a set of related
   information standards that may be used to represent machine (M2M) applications such as smart energy data and
   machine metadata in REST interfaces.. CoRE Link-format is a standard
   for doing Web Linking [RFC5988] in constrained environments.  SenML
   is a simple data model and representation format for composite and
   complex structured resources.  CoRE Link-Format and building
   automation. SenML can be used
   by CoAP [RFC7252] or HTTP servers.

   The discovery of resources offered by a constrained server is very
   important in machine-to-machine applications where there are no
   humans in the loop and static interfaces result in fragility.  The
   discovery loop.  Machine application clients must be able to
   adapt to different resource organizations without advance knowledge
   of resources provided the specific data structures hosted by an HTTP Web Server is typically
   called Web Linking [RFC5988]. each connected thing.  The
   use of Web Linking for the description and discovery of resources
   hosted by constrained web servers is specified by the CoRE Link Format [RFC6690] and can be
   used by CoAP [RFC7252] or HTTP servers.  The
   [RFC6690].  CoRE Link Format additionally defines
   an a link attribute
   for Interface Type ("if") that can be used to describe the REST
   interface of a resource, and may include a link to a description
   document.

   This
   memo describes how other specifications can combine document defines a set of Link Format compatible Interface Types
   for some common design patterns that enable the server side
   composition and organization, and client side discovery and
   consumption, of machine resources with using Web Linking.  An Interface
   Type may describe a
   well-known resource in terms of it's associated content
   formats, data types, URI templates, REST methods, parameters, and
   responses.  Basic interface to create new CoRE RESTful profiles. types are defined for sensors, actuators,
   and properties.  A CoRE
   profile set of collection types is based on defined for organizing

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   resources for discovery, and for various forms of bulk interaction
   with resource sets using typed embedding links.

   This document introduces the concept of Function Set, a Link Binding, which is defines
   a group of
   REST new link relation type to create a dynamic link between resources providing
   over which to exchange state updates.  Specifically, a service in Link Binding
   is a distributed system.  In
   addition, link for binding the notion state of Binding is introduced in order 2 resources together such that
   updates to create a
   synchronization one are sent over the link between two resources. to the other.  CoRE Link Format
   representations are used to configure, inspect, and maintain Link
   Bindings.  This document also additionally defines well-known interface descriptions a set of conditional
   Observe Attributes for Batch, Sensor,
   Parameter use with Link Bindings and Actuator types to compose new with the standalone
   CoRE Observe [RFC7641] method.

   Interface Types may be used in the composition of Function Sets or for
   standalone use and
   Profiles.  Function Sets and Profiles are described and an example is
   given of a sensor and actuator device profile using Function Sets
   composed from the Interface Types described in this document.

   This document describes a constrained web server. set of Interface Types which are referenced
   by the "if" link attribute and used to implement reusable design
   patterns and functional abstractions.  A short reference is
   provided for each type that can client discovering the "if"
   link attribute will be efficiently included in able to consume resources based on its
   knowledge of the expected interface description (if=) attribute types.  In this sense the
   Interface Type acts in a similar way as a Content-Format, but as a
   selector for a high level functional abstraction.  Interface types
   may also be provided with hypermedia controls and affordances to
   drive client interaction using the principles of HATEOAS.  In this
   case, the CoRE Link Format. Interface Types serve as constructor templates for resource
   organization and hypermedia annotation.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This specification requires readers to be familiar with all the terms
   and concepts that are discussed in [RFC5988] and [RFC6690].  This
   specification makes use of the following additional terminology:

   Interface Type:  A resource attribute which describes the interface
      exposed by the resource in terms of content formats, REST methods,
      parameters, and other related characteristics.

   Collection:  A resource which contains set of related resources,
      referenced by a list of links and optionally consisting of
      subresources.

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   Link Binding:  A unidirectional logical link between a source
      resource and a destination resource, over which state information
      is synchronized.

   Resource Discovery:  The process allowing a web client to identify
      resources being hosted on a web server.

   Gradual Reveal:  A REST design where resources are discovered
      progressively using Web Linking.

   Function Set:  A group of well-known REST resources that provides a
      particular service.

   Profile:  A group of well-known Function Sets defined by a
      specification.

   Device:  An IP smart object running a web server that hosts a group
      of Function Set instances from a profile.

   Service Discovery:  The process making it possible for a web client
      to automatically detect devices and Function Sets offered by these
      devices on a CoRE network.

   Resource Discovery:  The process allowing

3.  Interface Types

   An Interface Type definition may describe a web client to identify
      resources being hosted on a web server.

   Gradual Reveal:  A REST design where resources are discovered
      progressively using Web Linking.

   Binding:  A unidirectional logical link between a source resource and
      a destination resource.

3.  Function Set

   This section defines how a set in terms of it's
   associated content formats, data types, URI templates, REST resources can be created
   called a function set. methods,
   parameters, and responses.

4.  Collections

4.1.  Introduction to Collections

   A Function Set Collection is similar a resource which represents one or more related
   resources.  Within this document, a collection refers to a function block collection
   with characteristics defined in the sense that it this document.  A Collection
   Interface Type consists of input, output and parameter
   resources and contains internal logic.  A Function Set can have a
   subset set of mandatory inputs, outputs links and parameters a set of items pointed
   to provide minimum
   interoperability.  It can also by the links which may be extended with manufacturer/
   user-specific resources.  A device is composed of one or more
   Function Set instances.

   An example sub-resources of function sets can be found from the CoRE Resource
   Directory specification that defines REST interfaces for
   registration, group collection
   resource.  The collection types described in this document are Link
   List, Batch, Linked Batch, and lookup [I-D.ietf-core-resource-directory]. Hypermedia Collection.

   The OMA Lightweight M2M standard [REF] also defines links in a function set
   structure called an Objects that use integer path, instance collection are represented in CoRE Link-Format
   Content-Formats including JSON and
   resource URI segments.  OMA Objects can CBOR variants, and the items in
   the collection may be defined represented by senml, including JSON and then
   registered with an OMA maintained registry [REF].  This section is
   simply meant as CBOR
   variants.  In general, a guideline collection may support items of any
   available Content-Format.

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   A particular resource item may be a member of other such REST
   interfaces, either custom or part of other specifications.

3.1.  Defining more than one
   collection at a Function Set

   In time by being linked to, but may only be a Function Set, types
   subresource of resources are defined.  Each type
   includes a human readable name, a path template, a Resource Type for
   discovery, the Interface Definition one collection.

   Some collections may have pre-configured items and the data type links, and allowed
   values.  A Function Set definition some
   collections may also include a field
   indicating if a sub-resource is mandatory or optional.

3.1.1.  Path template

   A Function Set is a container resource under support dynamic creation and removal of items and
   links.  Likewise, modification of items in some collections may be
   permitted, and not in others.

   Collections may support link embedding, which its sub-resources
   are organized.  The profile defines is analogous to an
   image tag (link) causing the path image to each resource of display inline in a
   Function Set browser
   window.  Resources pointed to by embedded links in collections may be
   interacted with using bulk operations on the collection resource.
   For example, performing a path template.  The template can contain either
   relative paths or absolute paths depending GET on a collection resource may return a
   single representation containing all of the profile needs.  An
   absolute Function Set should linked resources.

   Links in collections may be located at its recommended root path
   on selected for processing by a web server, however it can particular
   request by using Query Filtering as described in CoRE Link-Format
   [RFC6690].

4.2.  Use Cases for Collections

   Collections may be located under used to provide gradual reveal of resources on an alternative path
   if necessary (for example multi-purpose devices, gateways etc.).  A
   relative Function Set can
   endpoint.  There may be instantiated as many times as needed on a web server with an arbitrary root path.  However some Function Sets
   (e.g. small set of links at the .well-known/core
   location, which may in turn point to other collections of resources
   that represent device description) only make sense as singletons.

   The path template includes a possible index {#} parameter, information, device configuration, device
   management, and
   possible fixed path segments.  The index {#} allows for multiple
   instances various functional clusters of this type of resource, and can be any string.  The root
   path and the indexes are resources on the only variable elements in a path
   template.  All other path segments should be fixed.

3.1.2.  Resource Type

   Each root
   device.

   A collection may provide resource of encapsulation, where link embedding
   may be used to provide a Function Set is assigned single resource with which a Resource Type
   parameter, therefore making it possible client may
   interact to discover it.  Each sub-
   resource of obtain a Function Set is also assigned set of related resource values.  For example, a Resource Type
   parameter.  This Resource Type is used
   collection for resource discovery manufacturer parameters may consist of manufacturer
   name, date of manufacture, location of manufacture, and is
   usually necessary to discover optional serial number
   resources supported on a
   specific device.  The Resource Type of which can be read as a Function Set single senml data object.

   A collection may also be used to group a set of like resources for service discovery and can bulk
   state update or actuation.  For example, the brightness control
   resources of a number of luminaries may be exported grouped by linking to DNS-SD [RFC6763]
   for example. them
   in a collection.  The Resource Type parameter defines the value collection type may support receiving a single
   update form a client and sending that should be included update to each resource item in
   the rt= field collection.

   Items may be sub-resources of the CoRE Link Format when describing a link to
   this collection resource.  The value SHOULD be  This enables
   updates to to multiple items in the form "namespace.type" collection to be processed
   together within the context of the collection resource.

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   root resources and "namespace.type.subtype" for sub-resources. Constrained October 2015

   Items may be dynamically created in a collection along with their
   hyperlinks.  This
   naming convention facilitates provides an "item factory" pattern which can serve
   as a resource type filtering with creation mechanism for dynamic resources.  This pattern
   is also useful for creating temporary resources for the
   /.well-known/core resource.  However a profile could allow mixing
   implementation of dynamic phenomena like commands, actions, and
   events using REST design patterns.  Item creation uses the collection
   Content-Format which allows specification of links and item state in
   foreign namespace references within
   a Function Set to import external
   references from other object models (e.g.  SenML and UCUM).

3.1.3.  Interface Description single representation.

4.3.  Content-Formats for Collections

   The Interface Description parameter defines collection interfaces by default use CoRE Link-Format for the REST interface
   link representations and SenML or text/plain for
   that type representations of resource.  Several base interfaces
   items.  The examples given are for collections that expose resources
   and links in these formats.  In addition, a new "collection" Content-
   Format is defined based on the SenML framework which represents both
   links and items in
   Section 5 the collection.

   The choice of this document.  For whether to return a given profile, the Interface
   Description may be inferred from representation of the Resource Type.  In that case links or of
   the
   Interface Description MAY be elided from link descriptions items or of
   resource types defined the collection format is determined by the accepts
   header option in the profile, but should be included for
   custom extensions to request.  Likewise, the profile.

   The root resource of a Function Set should provide a list choice of links to
   its sub-resources updating link
   metadata or item data or the collection resource itself is determined
   by the Content-Format option in order to offer gradual reveal the header of resources. the update request
   operation.

   The
   CoRE Link List interface defined default Content-Formats for collection types described in Section 5.1 offers this
   functionality so a root resource should support this interface or a
   derived interface like CoRE Batch (See Section 5.2).

3.1.4.  Data type

   The Data Type field defines the type of value (and possible range)
   that is returned in response to a GET for that resource or accepted
   with a PUT.  The interfaces defined
   document are:

   Links:  application/link-format, application/link-format+json

   Items:  application/senml+json, text/plain

   Collection:  application/collection+senml+json

4.4.  Links and Items in Section 5 make Collections

   Links use of plain
   text CoRE Link-Format representation by default and SenML Media types for the actual format of this data.  A
   profile may restrict point to
   any resource reachable from the list context of supported content types for the CoRE
   interfaces or define new interfaces with new content types.

3.2.  Discovery

   A device conforming to a profile SHOULD make its resources
   discoverable by providing collection.  This
   includes absolute links and links that point to other network
   locations if the context of the collection allows.  Links to sub-
   resources on in the path /.well-
   known/core collection MUST have a path-element starting with
   the resource name, as defined in [RFC6690].  All per RFC3986 [RFC3986].  Links to resources hosted on a device
   SHOULD be discoverable either in
   the global context MUST start with a direct link in /.well-known/core
   or by following successive links starting from /.well-known/core.

   The root path identifier
   [RFC5988].Links to other collections are formed per RFC3986.

   Examples of links:

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   </sen/>;if="core.lb"  : Link to the /sen/ collection describing it as
      a Function Set instance SHOULD be directly
   referenced core.lb type collection (Linked Batch)

   </sen/>;rel="grp"  : Link to the /sen/ collection indicating that
      /sen/ is a member of a group in /.well-known/core the collection in order which the link
      appears.

   <"/sen/temp">;rt="temperature"  : An absolute link to offer discovery the resource at
      the
   first discovery stage.  A device with more than 10 individual
   resources SHOULD only expose Function Set instances in /.well-known/
   core path /sen/temp

   <temp>;rt="temperature"  : Link to limit the size temp subresource of the
      collection in which this resource.

   In addition, a device MAY register its resources link appears.

   <temp>;anchor="/sen/"  : A link to a Resource
   Directory using the registration interface defined in
   [I-D.ietf-core-resource-directory] if such a directory temp subresource of the
      collection /sen/ which is available.

3.3.  Versioning

   A profile should track Function Set changes assumed not to avoid incompatibility
   issues.  Evolutions in a Function Set SHOULD be backward compatible.

4.  Bindings

   In a M2M RESTful environment, endpoints exchange the content subresource of their
   resources to operate the distributed system.  Beforehand, a
   configuration phase
      collection in which the link appears ,but is necessary expected to determine how be
      identified in the resources of collection by resource name.

   Links in the different endpoints are related to each other.  This can collection MAY be done
   either automatically Read, Updated, Added, or Removed using discovery mechanisms
   the CoRE Link-Format or by means of human
   intervention and a so-called commissioning tool.  In this document JSON Merge-Patch Content-Formats on the abstract relationship between two resources is called a Binding.

   The configuration phase necessitates
   collection resource.  Reading links uses the exchange GET method and returns
   an array or list containing the link-values of binding
   information so a format recognized by all CoRE endpoints is
   essential.  This document defines a format based on selected links.
   Links may be added to the CoRE Link-
   Format collection using POST or PATCH methods.
   Updates to represent binding information along with links MUST use the rules PATCH method and MAY use query
   filtering to
   define a binding select links for updating.  The PATCH method which on links
   MUST use the JSON Merge-Patch Content-Format (application/merge-
   patch+json) specified in RFC7396 [RFC7396] .

   Items in the collection SHOULD be represented using the SenML
   (application/senml+json) or plain text (text/plain) Content-Formats,
   depending on whether the representation is a specialized relationship between
   two resources.  The purpose of a binding is to synchronize the
   content between a source resource and a destination resource.  The
   destination resource single data point or
   multiple data points.  Items MAY be a group resource if represented using any supported
   Content-Format.

   Link Embedding enables the authority
   component bulk processing of items in the destination URI contains collection
   using a group address (either single operation targeting the collection resource.  A subset
   of resources in the collection may be selected for operation using
   Query Filtering.  Bulk Read operations using GET return a
   multicast address SenML
   representation of all selected resources.  Bulk item Update
   operations using PUT or a name that resolves POST apply the payload document to all
   selected resource items in the collection, using a multicast address).
   Since either a binding Batch or
   Group update policy.  A Batch update is unidirectional, performed by applying the binding entry defining a
   relationship is present only on one endpoint.  The binding entry may
   be located either on
   resource values in the source or payload document to all resources in the destination endpoint depending
   on
   collection that match any resource name in the binding method. payload document.
   Group updates are performed by applying the payload document to each
   item in the collection.  Group updates are indicated by the link
   relation type rel="grp" in the link.

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   The following table gives collection resource SHOULD represented using the
   collection+senml+json Content-Format.  The Hypermedia Collection type
   is the only collection type which supports this representation.
   Reading a summary collection using this content-format returns a
   representation of the
   binding methods described links and the items in the collection.
   Performing a POST operation using this Content-Format MAY create one
   or more detail new item(s) and their corresponding links in Section 4.2.

          +---------+------------+-------------+---------------+
          | Name    | Identifier | Location    | Method        |
          +---------+------------+-------------+---------------+
          | Polling | poll       | Destination | GET           |
          | Observe | obs        | Destination | GET + Observe |
          | Push    | push       | Source      | the collection.
   Performing a PUT           |
          +---------+------------+-------------+---------------+

4.1.  Format

   Since Binding lies in operation on this resource replaces the creation entire set
   of a link between two resources,
   Web Linking links and items with the CoRE Link-Format are a natural way to represent
   binding information. payload.  This involves the creation of a new relation
   type, purposely named "boundto".  In Content-Format is
   described in section Section 4.9.  Implementations MAY provide an
   alternate method using POST in a Web link with this relation
   type, Content-Format used by the target URI contains items in
   the location collection which creates a default link-value and system-assigned
   resource name.  Such implementations MAY create sub-resources of the source resource and
   collection resource.

4.5.  Queries on Collections

   Collections MAY support query filtering as defined in CoRE Link-
   Format [RFC6690].  Operations targeting either the context URI points to links or the destination resource.  The Web link
   attributes allow items
   MAY select a fine-grained control subset of links and items in the type of
   synchronization exchange along with collection by using
   query filtering.  The Content-Format specified in the conditions that trigger an
   update.  This specification defines request header
   selects whether links or items are targeted by the attributes below:

           +--------------------+-----------+------------------+
           | Attribute          | Parameter | Value            |
           +--------------------+-----------+------------------+
           | Binding method     | bind      | xsd:string       |
           | Minimum Period (s) | operation.

4.6.  Observing Collections

   Resource Observation using CoAP [RFC7252] MAY be supported on items
   in a collection.  A subset of the conditional observe parameters MAY
   be specified to apply.  In most cases pmin      | xsd:integer (>0) |
           | Maximum Period (s) | and pmax      | xsd:integer (>0) |
           | Change Step        | st        | xsd:decimal (>0) |
           | Greater Than       | gt        | xsd:decimal      |
           | Less Than          | lt        | xsd:decimal      |
           +--------------------+-----------+------------------+

   Bind Method:  This is are useful.
   Resource observation on a collection's items resource MAY report any
   changes of resource state in any item in the identifier collection.  Observation
   Responses, or notifications, SHOULD provide representations of the
   resources that have changed in SenML Content-Format.  Notifications
   MAY include multiple observations of a binding method which
      defines particular resource, with
   SenML time stamps indicating the rules observation times.

4.7.  Hypermedia Controls on Collections

   Additional Hypermedia controls may be defined to synchronize enable clients to
   automatically consume the destination resource.  This
      attribute is mandatory.

   Minimum Period:  When present, collection resources.  Typically, the minimum period indicates
   developer may map application level semantics onto collection
   operations.  For example, invoking an Action on an actuator may be
   defined as creating an Action item resource in a collection of
   Actions associated with the
      minimum time to wait (in seconds) before sending actuator, each item in the collection
   representing a new
      synchronization message (even if it has changed).  In past, current, or future action to be processed by the absence
      of this parameter,
   actuator.  Removing the minimum period is item could cancel any pending or curent long-
   running action, and removing a completed action could free up
   resources for new actions to be invoked.  A Hypermedia control for
   this pattern might provide a semantic name for the notifier.

   Maximum Period:  When present, action, for

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   example "Change Brightness", and might direct the maximum period indicates client to supply a
   SenML representation of parameters for the
      maximum time action as well as provide
   instructions on what method (POST) to use and how to construct the
   URI (the collection URI in seconds between two consecutive syncronization
      messages (regardless this case) if it has changed).  In the absence required.  An example of
   this
      parameter, the maximum period hypermedia control is up to shown below.

4.8.  Collection Types

   There are four collection types defined in this document:

   +---------------------+----------+----------------------------------+
   |     Collection Type | if=      | Content-Formats                  |
   +---------------------+----------+----------------------------------+
   |           Link List | core.ll  | link-format                      |
   |               Batch | core.b   | link-format, senml               |
   |        Linked Batch | core.lb  | link-format, senml               |
   |          Hypermedia | core.hc  | link-format, senml,              |
   |          Collection |          | collection+senml                 |
   |             Binding | core.bnd | link-format                      |
   +---------------------+----------+----------------------------------+

   Each collection type MAY support a subset of the notifier.  The maximum
      period MUST be greater than methods and
   functions described above.  For the minimum period parameter (if
      present).

   Change Step:  When present, first three collection types, the change step indicates how much
   methods and functions are defined in the
      value of a resource corresponding Interface
   Description.  The Hypermedia Collection SHOULD change before sending a new
      notification (compared expose hypermedia
   controls to the value applications to indicate which methods and functions are
   supported.

4.9.  The collection+senml+json Content-Format

   The collection+senml+json Content-Format is used to represent all of
   the last notification). attributes and resources of a collection in a single format.
   This parameter has lower priority than is accomplished by extending the period parameters, thus
      even if SenmL format by adding a links
   element "l".  The links element is formatted as an array of links in
   the change step has been fulfilled, application/link-format+json Content-Format with the time since tag "l"
   which follows the
      last notification SHOULD be between pmin structure of the "e" element.  An example of this
   format is given below.

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   {
     "bn":"/ep/sen/"
     "e":[
       { "n": "light", "v": 123, "u": "lx" },
       { "n": "temp", "v": 27.2, "u": "degC" },
       { "n": "humidity", "v": 80, "u": "%RH" }],
     "l":[
       { "href":"/ep/sen/", "rel":"self", "if": "core.hc", "rt": "ms" },
       { "href":"light", "rt":"core.s" },
       { "href":"temp", "rt":"core.s" },
       { "href":"humidity", "rt":"core.s" }]
   }

5.  Link Bindings and pmax.

   Greater Than:  When present, Greater Than indicates Observe Attributes

   In a M2M RESTful environment, endpoints may directly exchange the upper limit
      value
   content of their resources to operate the distributed system.  For
   example, a light switch may supply on-off control information that
   may be sent directly to a light resource value SHOULD cross before sending for on-off control.
   Beforehand, a new
      notification.  This parameter has lower priority than the period
      parameters, thus even if the Greater Than limit has been crossed, configuration phase is necessary to determine how the time since
   resources of the last notification SHOULD different endpoints are related to each other.  This
   can be between pmin done either automatically using discovery mechanisms or by
   means of human intervention and
      pmax.

   Less Than:  When present, Less Than indicates the lower limit value
      the resource value SHOULD cross before sending a new notification.
      This parameter has lower priority than the period parameters, thus
      even if the Less Than limit has been crossed, the time since so-called commissioning tool.  In
   this document the
      last notification SHOULD be abstract relationship between pmin and pmax.

4.2.  Binding methods

   A two resources is
   called a link Binding.  The configuration phase necessitates the
   exchange of binding method information so a format recognized by all CoRE
   endpoints is essential.  This document defines a format based on the
   CoRE Link-Format to represent binding information along with the
   rules to generate define a binding method which is a specialized relationship
   between two resources.  The purpose of a binding is to synchronize
   the web-transfer
   exchanges that will effectively send content from the between a source resource
   to the and a destination resource.
   The description of destination resource MAY be a binding method
   must define group resource if the following aspects:

   Identifier:  This is value authority
   component of the "bind" attribute used destination URI contains a group address (either a
   multicast address or a name that resolves to identify
      the method.

   Location:  This information indicates whether a multicast address).
   Since a binding is unidirectional, the binding entry defining a
   relationship is
      stored present only on one endpoint.  The binding entry may
   be located either on the source or on the destination endpoint.

   REST Method:  This is the REST method used in endpoint depending
   on the Request/Response
      exchanges.

   Conditions:  A binding method definition must state how the condition
      attributes method.  The following table gives a summary of the abstract binding definition are actually used in
      this specialized binding.

   This specification supports 3
   binding methods described below.

   Polling:  The in more detail in Section 5.2.

          +---------+------------+-------------+---------------+
          | Name    | Identifier | Location    | Method        |
          +---------+------------+-------------+---------------+
          | Polling method consists of sending periodic | poll       | Destination | GET
      requests from           |
          | Observe | obs        | Destination | GET + Observe |
          | Push    | push       | Source      | PUT           |
          +---------+------------+-------------+---------------+

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5.1.  Format

   Since Binding involves the destination endpoint creation of a link between two resources,
   Web Linking and the CoRE Link-Format are a natural way to represent
   binding information.  This involves the creation of a new relation
   type, purposely named "boundto".  In a Web link with this relation
   type, the target URI contains the location of the source resource and
      copying
   the content context URI points to the destination resource.  The binding
      entry for this method MUST be stored on the destination endpoint.
      The destination endpoint MUST ensure that the polling frequency
      does not exceed the limits defined by the pmin and pmax Web link
   attributes allow a fine-grained control of the binding entry.  The copying process MAY filter out content
      from type of
   synchronization exchange along with the GET requests using value-based conditions (e.g that trigger an
   update.  This specification defines the attributes below:

           +--------------------+-----------+------------------+
           | Attribute          | Parameter | Value            |
           +--------------------+-----------+------------------+
           | Binding method     | bind      | xsd:string       |
           | Minimum Period (s) | pmin      | xsd:integer (>0) |
           | Maximum Period (s) | pmax      | xsd:integer (>0) |
           | Change
      Step, Less Than, Step        | st        | xsd:decimal (>0) |
           | Greater Than).

   Observe:  The Observe Than       | gt        | xsd:decimal      |
           | Less Than          | lt        | xsd:decimal      |
           +--------------------+-----------+------------------+

   Bind Method:  This is the identifier of a binding method relies on which
      defines the Publish/Subscribe pattern
      thus an observation relationship is created between rules to synchronize the destination endpoint and the source resource.  On each
      notification  This
      attribute is mandatory.

   Minimum Period:  When present, the content from minimum period indicates the source resource is copied
      minimum time to wait (in seconds) before sending a new
      synchronization message (even if it has changed).  In the
      destination resource.  The creation absence
      of this parameter, the observation
      relationship requires minimum period is up to the CoAP Observation mechanism
      [I-D.ietf-core-observe] hence notifier.

   Maximum Period:  When present, the maximum period indicates the
      maximum time in seconds between two consecutive state
      synchronization messages (regardless if it has changed).  In the
      absence of this method parameter, the maximum period is only permitted when up to the resources are made available over CoAP.
      notifier.  The binding entry for
      this method maximum period MUST be stored on greater than the destination endpoint.  The
      binding conditions are mapped as query string parameters (see
      Section 5.9).

   Push: minimum
      period parameter (if present).

   Change Step:  When present, the Push method is assigned to a binding, change step indicates how much the source
      endpoint sends PUT requests
      value of a resource SHOULD change before sending a new
      notification (compared to the destination resource when value of the
      binding condition attributes are satisfied for last notification).
      This parameter has lower priority than the source
      resource.  The source endpoint MUST only send a notification
      request period parameters, thus
      even if the binding conditions are met.  The binding entry for
      this method MUST be stored on the source endpoint.

4.3.  Binding table

   The binding table is a special resource that gives access to change step has been fulfilled, the
   bindings on a endpoint.  A binding table resource MUST support time since the
   Binding interface defined in Section 5.8.  A profile
      last notification SHOULD allow
   only one be between pmin and pmax.

   Greater Than:  When present, Greater Than indicates the upper limit
      value the resource table per endpoint.

5. value SHOULD cross before sending a new

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   This section defines REST interfaces Definitions for Link List, Batch, Sensor,
   Parameter, Actuator Constrained October 2015

      notification.  This parameter has lower priority than the period
      parameters, thus even if the Greater Than limit has been crossed,
      the time since the last notification SHOULD be between pmin and Binding table resources.  Variants such as
   Linked Batch or Read-Only Parameter are also presented.  Each type is
   described along with its Interface Description attribute
      pmax.

   Less Than:  When present, Less Than indicates the lower limit value and
   valid methods.  These are defined for each interface in
      the table
   below.  These interfaces can support plain text and/or SenML Media
   types.

   The if= column resource value SHOULD cross before sending a new notification.
      This parameter has lower priority than the period parameters, thus
      even if the Less Than limit has been crossed, the time since the
      last notification SHOULD be between pmin and pmax.

5.2.  Binding methods

   A binding method defines the Interface Description (if=) attribute
   value rules to be used in generate the CoRE Link Format for a web-transfer
   exchanges that will effectively send content from the source resource conforming
   to
   that interface.  When this value appears in the if= attribute destination resource.  The description of a
   link, the resource MUST support binding method
   must define the corresponding REST interface
   described in this section.  The resource MAY support additional
   functionality, which following aspects:

   Identifier:  This is out value of scope for this specification.
   Although these interface descriptions are intended to be the "bind" attribute used with to identify
      the CoRE Link Format, they are applicable for use in any REST
   interface definition.

   The Methods column defines method.

   Location:  This information indicates whether the methods supported by that interface,
   which are described in more detail below.

   +-------------------+----------+------------------------------------+
   |         Interface | if=      | Methods                            |
   +-------------------+----------+------------------------------------+
   |         Link List | core.ll  | GET                                |
   |             Batch | core.b   | GET, PUT, POST (where applicable)  |
   |      Linked Batch | core.lb  | GET, PUT, POST, DELETE (where      |
   |                   |          | applicable)                        |
   |            Sensor | core.s   | GET                                |
   |         Parameter | core.p   | GET, PUT                           |
   |         Read-only | core.rp  | GET                                |
   |         Parameter |          |                                    |
   |          Actuator | core.a   | GET, PUT, POST                     |
   |           Binding | core.bnd | GET, POST, DELETE                  |
   +-------------------+----------+------------------------------------+

   The following binding entry is an example of links in
      stored on the CoRE Link Format using
   these interface descriptions.  The resource hierarchy is based source or on a
   simple profile defined the destination endpoint.

   REST Method:  This is the REST method used in Appendix A.  These links the Request/Response
      exchanges.

   Conditions:  A binding method definition must state how the condition
      attributes of the abstract binding definition are actually used in the
   subsequent examples
      this specialized binding.

   This specification supports 3 binding methods described below.

   Req: GET /.well-known/core
   Res: 2.05 Content (application/link-format)
   </s>;rt="simple.sen";if="core.b",
   </s/lt>;rt="simple.sen.lt";if="core.s",
   </s/tmp>;rt="simple.sen.tmp";if="core.s";obs,
   </s/hum>;rt="simple.sen.hum";if="core.s",
   </a>;rt="simple.act";if="core.b",
   </a/1/led>;rt="simple.act.led";if="core.a",
   </a/2/led>;rt="simple.act.led";if="core.a",
   </d>;rt="simple.dev";if="core.ll",
   </l>;if="core.lb",

5.1.  Link List

   Polling:  The Link List interface is used to retrieve (GET) a list Polling method consists of resources
   on a web server.  The sending periodic GET request SHOULD contain an Accept option
   with
      requests from the application/link-format content type, however if destination endpoint to the source resource and
      copying the content to the destination resource.  The binding
      entry for this method MUST be stored on the destination endpoint.
      The destination endpoint MUST ensure that the polling frequency
      does not support any other form exceed the limits defined by the pmin and pmax attributes
      of GET methods the Accept
   option binding entry.  The copying process MAY be elided. filter out content
      from the GET requests using value-based conditions (e.g Change
      Step, Less Than, Greater Than).

   Observe:  The Accept option SHOULD only include Observe method creates an observation relationship
      between the destination endpoint and the source resource.  On each
      notification the
   application/link-format content type. from the source resource is copied to the
      destination resource.  The request returns a list creation of
   URI references with absolute paths to the observation
      relationship requires the CoAP Observation mechanism [RFC7641]

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      hence this method is only permitted when the resources are made
      available over CoAP.  The binding entry for this method MUST be
      stored on the destination endpoint.  The binding conditions are
      mapped as defined in
   CoRE Link Format.  This interface query string parameters (see Section 5.4).

   Push:  When the Push method is typically used with a parent
   resource to enumerate sub-resources but may be used assigned to reference any
   resource on a web server.

   Link List is binding, the base interface source
      endpoint sends PUT requests to provide gradual reveal of
   resources on a CoRE web server, hence the root destination resource of a Function
   Set SHOULD implement this interface or an extension of this
   interface. when the
      binding condition attributes are satisfied for the source
      resource.  The following example interacts with source endpoint MUST only send a Link List /d containing
   Parameter sub-resources /d/name, /d/model.

   Req: GET /d (Accept:application/link-format)
   Res: 2.05 Content (application/link-format)
   </d/name>;rt="simple.dev.n";if="core.p",
   </d/model>;rt="simple.dev.mdl";if="core.rp"

5.2.  Batch notification
      request if the binding conditions are met.  The Batch interface binding entry for
      this method MUST be stored on the source endpoint.

5.3.  Binding table

   The binding table is used a special resource that gives access to manipulate the
   bindings on a collection of sub-
   resources at endpoint.  A binding table resource MUST support the same time.  The Batch
   Binding interface type supports defined in Section 6.9.  A profile SHOULD allow
   only one resource table per endpoint.

5.4.  Resource Observation Attributes

   When resource interfaces following this specification are made
   available over CoAP, the
   same methods as its sub-resources, and can CoAP Observation mechanism [RFC7641] MAY be
   used to read (GET), set
   (PUT) or toggle (POST) the values of those sub-resource with observe any changes in a single
   resource representation.  The sub-resources of resource, and receive asynchronous
   notifications as a Batch MAY be
   heterogeneous, result.  In addition, a method used on the Batch only applies set of query string
   parameters are defined here to sub-
   resources that support it.  For example Sensor interfaces do not
   support PUT, and thus allow a PUT request client to control how often a Sensor member of that Batch
   would be ignored.  A batch requires the use of SenML Media types in
   order to support multiple sub-resources.

   In addition, The Batch interface
   client is an extension of the Link List
   interface and interested in consequence MUST support the same methods.

   The following example interacts with a Batch /s with Sensor sub-
   resources /s/light, /s/temp receiving notifications and /s/humidity.

   Req: GET /s
   Res: 2.05 Content (application/senml+json)
   {"e":[
       { "n": "light", "v": 123, "u": "lx" },
       { "n": "temp", "v": 27.2, "u": "degC" },
       { "n": "humidity", "v": 80, "u": "%RH" }],
   }

5.3.  Linked Batch

   The Linked Batch interface is an extension of how much a
   resource value should change for the Batch interface.
   Contrary new representation to be
   interesting.  These query parameters are described in the basic Batch which is a collection statically defined
   by the web server, a Linked Batch is dynamically controlled by a web
   client. following
   table.  A Linked Batch resource has no sub-resources.  Instead the using an interface description defined in this
   specification and marked as Observable in its link description SHOULD
   support these observation parameters.  The Change Step parameter can
   only be supported on resources forming the batch with an atomic numeric value.

   These query parameters MUST be treated as resources that are referenced read
   using Web Linking
   [RFC5988] GET and the CoRE Link Format [RFC6690].  A request with a POST
   method updated using PUT, and a content type of application/link-format simply appends
   new resources to the collection.  The links MUST NOT be included in the payload MUST
   reference a resource on
   Observe request.  Multiple parameters MAY be updated at the web server with an absolute path.  A
   DELETE request empties same time
   by including the current collection values in the query string of links.  All other
   requests available for a basic Batch are still valid PUT.  Before being
   updated, these parameters have no default value.

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   Batch.

   The following example interacts with a Linked Batch /l and creates a
   collection containing /s/light, /s/temp and Constrained October 2015

         +----------------+------------------+------------------+
         | Resource       | Parameter        | Data Format      |
         +----------------+------------------+------------------+
         | Minimum Period | /{resource}?pmin | xsd:integer (>0) |
         | Maximum Period | /{resource}?pmax | xsd:integer (>0) |
         | Change Step    | /{resource}?st   | xsd:decimal (>0) |
         | Less Than      | /{resource}?lt   | xsd:decimal      |
         | Greater Than   | /{resource}?gt   | xsd:decimal      |
         +----------------+------------------+------------------+

   Minimum Period:  When present, the minimum period indicates the
      minimum time to wait (in seconds) before sending a new
      synchronization message (even if it has changed).  In the absence
      of this parameter, the minimum period is up to the notifier.

   Maximum Period:  When present, the maximum period indicates the
      maximum time in seconds between two consecutive state
      synchronization messages (regardless if it has changed).  In the
      absence of this parameter, the maximum period is up to the
      notifier.  The maximum period MUST be greater than the minimum
      period parameter (if present).

   Change Step:  When present, the change step indicates how much the
      value of a resource SHOULD change before sending a new
      notification (compared to the value of the last notification).
      This parameter has lower priority than the period parameters, thus
      even if the change step has been fulfilled, the time since the
      last notification SHOULD be between pmin and pmax.

   Greater Than:  When present, Greater Than indicates the upper limit
      value the resource value SHOULD cross before sending a new
      notification.  This parameter has lower priority than the period
      parameters, thus even if the Greater Than limit has been crossed,
      the time since the last notification SHOULD be between pmin and
      pmax.

   Less Than:  When present, Less Than indicates the lower limit value
      the resource value SHOULD cross before sending a new notification.
      This parameter has lower priority than the period parameters, thus
      even if the Less Than limit has been crossed, the time since the
      last notification SHOULD be between pmin and pmax.

6.  Interface Descriptions

   This section defines REST interfaces for Link List, Batch, Sensor,
   Parameter, Actuator and Binding table resources.  Variants such as
   Linked Batch or Read-Only Parameter are also presented.  Each type is
   described along with its Interface Description attribute value and

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   valid methods.  These are defined for each interface in the table
   below.  These interfaces can support plain text and/or SenML Media
   types.

   The if= column defines the Interface Description (if=) attribute
   value to be used in the CoRE Link Format for a resource conforming to
   that interface.  When this value appears in the if= attribute of a
   link, the resource MUST support the corresponding REST interface
   described in this section.  The resource MAY support additional
   functionality, which is out of scope for this specification.
   Although these interface descriptions are intended to be used with
   the CoRE Link Format, they are applicable for use in any REST
   interface definition.

   The Methods column defines the methods supported by that interface,
   which are described in more detail below.

   +-----------------+----------+-----------------+--------------------+
   |       Interface | if=      | Methods         | Content-Formats    |
   +-----------------+----------+-----------------+--------------------+
   |       Link List | core.ll  | GET             | link-format        |
   |           Batch | core.b   | GET, PUT, POST  | link-format, senml |
   |    Linked Batch | core.lb  | GET, PUT, POST, | link-format, senml |
   |                 |          | DELETE          |                    |
   |          Sensor | core.s   | GET             | link-format,       |
   |                 |          |                 | text/plain         |
   |       Parameter | core.p   | GET, PUT        | link-format,       |
   |                 |          |                 | text/plain         |
   |       Read-only | core.rp  | GET             | link-format,       |
   |       Parameter |          |                 | text/plain         |
   |        Actuator | core.a   | GET, PUT, POST  | link-format,       |
   |                 |          |                 | text/plain         |
   |         Binding | core.bnd | GET, POST,      | link-format        |
   |                 |          | DELETE          |                    |
   +-----------------+----------+-----------------+--------------------+

   The following is an example of links in the CoRE Link Format using
   these interface descriptions.  The resource hierarchy is based on a
   simple profile defined in Appendix A.  These links are used in the
   subsequent examples below.

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   Req: GET /.well-known/core
   Res: 2.05 Content (application/link-format)
   </s/>;rt="simple.sen";if="core.b",
   </s/lt>;rt="simple.sen.lt";if="core.s",
   </s/tmp>;rt="simple.sen.tmp";if="core.s";obs,
   </s/hum>;rt="simple.sen.hum";if="core.s",
   </a/>;rt="simple.act";if="core.b",
   </a/1/led>;rt="simple.act.led";if="core.a",
   </a/2/led>;rt="simple.act.led";if="core.a",
   </d/>;rt="simple.dev";if="core.ll",
   </l/>;if="core.lb",

6.1.  Link List

   The Link List interface is used to retrieve (GET) a list of resources
   on a web server.  The GET request SHOULD contain an Accept option
   with the application/link-format content format; however if the
   resource does not support any other form of GET methods the Accept
   option MAY be elided.  The Accept option SHOULD only include the
   application/link-format content format.  The request returns a list
   of URI references with absolute paths to the resources as defined in
   CoRE Link Format.  This interface is typically used with a parent
   resource to enumerate sub-resources but may be used to reference any
   resource on a web server.

   Link List is the base interface to provide gradual reveal of
   resources on a CoRE web server, hence the root resource of a Function
   Set SHOULD implement this interface or an extension of this
   interface.

   The following example interacts with a Link List /d containing
   Parameter sub-resources /d/name, /d/model.

   Req: GET /d/ (Accept:application/link-format)
   Res: 2.05 Content (application/link-format)
   </d/name>;rt="simple.dev.n";if="core.p",
   </d/model>;rt="simple.dev.mdl";if="core.rp"

6.2.  Batch

   The Batch interface is used to manipulate a collection of sub-
   resources at the same time.  The Batch interface type supports the
   same methods as its sub-resources, and can be used to read (GET),
   update (PUT) or apply (POST) the values of those sub-resource with a
   single resource representation.  The sub-resources of a Batch MAY be
   heterogeneous, a method used on the Batch only applies to sub-

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   resources that support it.  For example Sensor interfaces do not
   support PUT, and thus a PUT request to a Sensor member of that Batch
   would be ignored.  A batch requires the use of SenML Media types in
   order to support multiple sub-resources.

   In addition, The Batch interface is an extension of the Link List
   interface and in consequence MUST support the same methods.

   The following example interacts with a Batch /s/ with Sensor sub-
   resources /s/light, /s/temp and /s/humidity.

   Req: GET /s/
   Res: 2.05 Content (application/senml+json)
   {"e":[
       { "n": "light", "v": 123, "u": "lx" },
       { "n": "temp", "v": 27.2, "u": "degC" },
       { "n": "humidity", "v": 80, "u": "%RH" }],
   }

6.3.  Linked Batch

   The Linked Batch interface is an extension of the Batch interface.
   Contrary to the basic Batch which is a collection statically defined
   by the web server, a Linked Batch is dynamically controlled by a web
   client.  A Linked Batch resource has no sub-resources.  Instead the
   resources forming the batch are referenced using Web Linking
   [RFC5988] and the CoRE Link Format [RFC6690].  A request with a POST
   method and a content format of application/link-format simply appends
   new resource links to the collection.  The links in the payload MUST
   reference a resource on the web server with an absolute path.  A
   DELETE request removes the entire collection.  All other requests
   available for a basic Batch are still valid for a Linked Batch.

   The following example interacts with a Linked Batch /l/ and creates a
   collection containing /s/light, /s/temp and /s/humidity in 2 steps.

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   Req: POST /l (Content-type: /l/ (Content-Format: application/link-format)
   </s/light>,</s/temp>
   Res: 2.04 Changed

   Req: GET /l /l/
   Res: 2.05 Content (application/senml+json)
   {"e":[
      { "n": "/s/light", "v": 123, "u": "lx" },
      { "n": "/s/temp", "v": 27.2, "u": "degC" },
   }

   Req: POST /l (Content-type: /l/ (Content-Format: application/link-format)
   </s/humidity>
   Res: 2.04 Changed

   Req: GET /l /l/ (Accept: application/link-format)
   Res: 2.05 Content (application/link-format)
   </s/light>,</s/temp>,</s/humidity>

   Req: GET /l /l/
   Res: 2.05 Content (application/senml+json)
   {"e":[
      { "n": "/s/light", "v": 123, "u": "lx" },
      { "n": "/s/temp", "v": 27.2, "u": "degC" },
      { "n": "/s/humidity", "v": 80, "u": "%RH" }],
   }

   Req: DELETE /l /l/
   Res: 2.04 Changed

5.4. 2.02 Deleted

6.4.  Hypermedia Collection

   The Hypermedia Collection interface MAY provide a full set of the
   methods and link relation types described in section Section 4 of
   this document.

   The following example interacts with a Hypermedia Collection at
   /act1/actions/ by creating a new resource with Parameter sub-
   resources newVal, tTime.  The example depicts an actuation operation
   with a new actuator value of 86.3% and a transition time of 10
   seconds.  The returned location of the created resource is then read,
   and a response is returned which includes the remaining time for the
   operation to complete "rTime".  Then, the operation is cancelled by
   sending a DELETE operation to the location of the created resource
   that represents the running action.

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   Req: POST /Act1/Actions/
   Content-Format: application/collection+senml_json
   Pl: [{"n":newVal", "v":86.3}, {"n":tTime", "v":10}]
   Res: 2.01 Created
   Location: Action1234

   Req: GET /Act1/Actions/Action1234
   Accepts: application/senml+json
   Res: 2.05 Content
   Pl: [{"n":newVal", "v":86.3},
        {"n":tTime", "v":10},
        {"n":"rTime", "v":"8.87"}]

   Req: DELETE /Act1/Actions/Action1234
   Res: 2.02 Deleted

   Req: GET /Act1/Actions/Action1234
   Res: 4.04 Not Found

6.5.  Sensor

   The Sensor interface allows the value of a sensor resource to be read
   (GET).  The Media type of the resource can be either plain text or
   SenML.  Plain text MAY be used for a single measurement that does not
   require meta-data.  For a measurement with meta-data such as a unit
   or time stamp, SenML SHOULD be used.  A resource with this interface
   MAY use SenML to return multiple measurements in the same
   representation, for example a list of recent measurements.

   The following are examples of Sensor interface requests in both text/
   plain and application/senml+json.

   Req: GET /s/humidity (Accept: text/plain)
   Res: 2.05 Content (text/plain)
   80

   Req: GET /s/humidity (Accept: application/senml+json)
   Res: 2.05 Content (application/senml+json)
   {"e":[
       { "n": "humidity", "v": 80, "u": "%RH" }],
   }

5.5.

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6.6.  Parameter

   The Parameter interface allows configurable parameters and other
   information to be modeled as a resource.  The value of the parameter
   can be read (GET) or set update (PUT).  Plain text or SenML Media types
   MAY be returned from this type of interface.

   The following example shows request for reading and setting updating a
   parameter.

   Req: GET /d/name
   Res: 2.05 Content (text/plain)
   node5

   Req: PUT /d/name (text/plain)
   outdoor
   Res: 2.04 Changed

5.6.

6.7.  Read-only Parameter

   The Read-only Parameter interface allows configuration parameters to
   be read (GET) but not set. updated.  Plain text or SenML Media types MAY
   be returned from this type of interface.

   The following example shows request for reading such a parameter.

   Req: GET /d/model
   Res: 2.05 Content (text/plain)
   SuperNode200

6.8.  Actuator

   The Actuator interface is used by resources that model different
   kinds of actuators (changing its value has an effect on its
   environment).  Examples of actuators include for example LEDs,
   relays, motor controllers and light dimmers.  The current value of
   the actuator can be read (GET) or the actuator value can be updated
   (PUT).  In addition, this interface allows the use of POST to change
   the state of an actuator, for example to toggle between its possible
   values.  Plain text or SenML Media types MAY be returned from this
   type of interface.  A resource with this interface MAY use SenML to
   include multiple measurements in the same representation, for example
   a list of recent actuator values or a list of values to updated.

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   The following example shows requests for reading, setting and
   toggling an actuator (turning on a led).

   Req: GET /a/1/led
   Res: 2.05 Content (text/plain)
   0

   Req: PUT /a/1/led (text/plain)
   1
   Res: 2.04 Changed

   Req: POST /a/1/led (text/plain)
   Res: 2.04 Changed

   Req: GET /a/1/led
   Res: 2.05 Content (text/plain)
   0

6.9.  Binding

   The Binding interface is used to manipulate a binding table.  A
   request with a POST method and a content format of application/link-
   format simply appends new bindings to the table.  All links in the
   payload MUST have a relation type "boundTo".  A GET request simply
   returns the current state of a binding table whereas a DELETE request
   empties the table.

   The following example shows request requests for reading such adding, retrieving and
   deleting bindings in a parameter. binding table.

   Req: POST /bnd/ (Content-Format: application/link-format)
   <coap://sensor.example.com/s/light>;
     rel="boundto";anchor="/a/light";bind="obs";pmin="10";pmax="60"
   Res: 2.04 Changed

   Req: GET /d/model /bnd/
   Res: 2.05 Content (text/plain)
   SuperNode200

5.7.  Actuator

   The Actuator interface (application/link-format)
   <coap://sensor.example.com/s/light>;
     rel="boundto";anchor="/a/light";bind="obs";pmin="10";pmax="60"

   Req: DELETE /bnd/
   Res: 2.04 Changed

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6.10.  Future Interfaces

   It is used by resources expected that model different
   kinds of actuators (changing its value has an effect on its
   environment).  Examples further interface descriptions will be defined in
   this and other specifications.

6.11.  WADL Description

   This section defines the formal Web Application Description Langauge
   (WADL) definition of actuators include these CoRE interface descriptions.

<?xml version="1.0" standalone="yes"?>

<application xmlns="http://research.sun.com/wadl/2006/10"
             xmlns:xsd="http://www.w3.org/2001/XMLSchema"
             xmlns:senml="urn:ietf:params:xml:ns:senml">

  <grammars>
    <include href="http://tools.ietf.org/html/draft-jennings-senml"/>
  </grammars>

  <doc title="CoRE Interfaces"/>

  <resource_type id="s">
    <doc title="Sensor interface type"/>
    <method href="#read"/>
    <method href="#observe"/>
    <method href="#observe-cancel"/>
    <method href="#getattr"/>
    <method href="#setattr"/>
  </resource_type>

  <resource_type id="p">
    <doc title="Parameter interfacee type"/>
    <method href="#read"/>
    <method href="#observe"/>
    <method href="#observe-cancel"/>
    <method href="#getattr"/>
    <method href="#setattr"/>
    <method href="#update"/>
  </resource_type>

  <resource_type id="rp">
    <doc title="Read-only Parameter interface type"/>
    <method href="#read"/>
    <method href="#observe"/>
    <method href="#observe-cancel"/>
    <method href="#getattr"/>

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   relays, motor controllers Constrained October 2015

    <method href="#setattr"/>
  </resource_type>

  <resource_type id="a">
    <doc title="Actuator interface type"/>
    <method href="#read"/>
    <method href="#observe"/>
    <method href="#observe-cancel"/>
    <method href="#getattr"/>
    <method href="#setattr"/>
    <method href="#update"/>
    <method href="#apply"/>
  </resource_type>

  <resource_type id="ll">
    <doc title="Link List interface type"/></doc>
    <method href="#listLinks"/>
  </resource_type>

  <resource_type id="b">
    <doc title="Batch of sub-resources interface type">The methods read,
     observe, update and light dimmers. apply are applied to each sub-
     resource of the requested resource that supports it. Mixed
     sub-resource types can be supported.</doc>
    <method href="#read"/>
    <method href="#observe"/>
    <method href="#observe-cancel"/>
    <method href="#getattr"/>
    <method href="#setattr"/>
    <method href="#update"/>
    <method href="#apply"/>
    <method href="#listLinks"/>
  </resource_type>

  <resource_type id="lb">
    <doc title="Linked Batch interface type">. The current value methods read,
     obervableRead, update and apply are applied to each linked
     resource of the actuator requested resource that supports it. Mixed
     linked resource types can be read (GET) or a new actuator value set (PUT).  In
   addition, this supported.</doc>
    <method href="#read"/>
    <method href="#observe"/>
    <method href="#observe-cancel"/>
    <method href="#getattr"/>
    <method href="#setattr"/>
    <method href="#update"/>
    <method href="#apply"/>
    <method href="#listLinks"/>
    <method href="#appendLinks"/>

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    <method href="#clearLinks"/>
  </resource_type>

  <resource_type id="hc">
    <doc title="Hypermedia Collection interface defines the use of POST (with no body) to
   toggle an actuator between its possible values.  Plain text or SenML
   Media types MAY be returned from this type of interface.  A type">.</doc>
    <method href="#read"/>
    <method href="#observe"/>
    <method href="#observe-cancel"/>
    <method href="#getattr"/>
    <method href="#setattr"/>
    <method href="#update"/>
    <method href="#apply"/>
    <method href="#listLinks"/>
    <method href="#appendLinks"/>
    <method href="#clearLinks"/>
    <method href="#updateLinks"/>
    <method href="#readCollection"/>
    <method href="#addItem"/>
  </resource_type>

  <resource_type id="bnd">
    <doc title="Binding table resource
   with this interface MAY use SenML to include multiple measurements in
   the same representation, for example a list of recent actuator values
   or a type">A modifiable list of values to set.

   The following example shows requests for reading, setting and
   toggling an actuator (turning on a led).

   Req: GET /a/1/led
   Res: 2.05 Content (text/plain)
   0

   Req: PUT /a/1/led (text/plain)
   1
   Res: 2.04 Changed

   Req: POST /a/1/led (text/plain)
   Res: 2.04 Changed

   Req: GET /a/1/led
   Res: 2.05 Content (text/plain)
   0

5.8.  Binding

   The Binding interface is used to manipulate a binding table.  A
   request with a POST method and a content type of application/
   link-format simply appends new bindings to the table.  All links in
   the payload
    links. Each link MUST have a the relation type "boundTo".  A GET request
   simply returns "boundTo".</doc>
    <method href="#listLinks"/>
    <method href="#appendLinks"/>
    <method href="#clearLinks"/>
  </resource_type>

  <method id="read" name="GET">
    <doc>Retrieve the current state value of a binding table whereas sensor, an actuator or a DELETE
   request empties the table.

   The following example shows requests for adding, retrieving parameter.
     Both HTTP and
   deleting bindings in a binding table.

   Req: POST /bnd (Content-type: application/link-format)
   <coap://sensor.example.com/s/light>;
     rel="boundto";anchor="/a/light";bind="obs";pmin="10";pmax="60"
   Res: 2.04 Changed

   Req: GET /bnd
   Res: 2.05 Content (application/link-format)
   <coap://sensor.example.com/s/light>;
     rel="boundto";anchor="/a/light";bind="obs";pmin="10";pmax="60"

   Req: DELETE /bnd
   Res: 2.04 Changed

5.9.  Resource Observation Attributes

   When resource interfaces following CoAP support this specification are made
   available over CoAP, method.</doc>
    <request>
    </request>
    <response status="200">
      <representation mediaType="text/plain"/>
      <representation mediaType="application/senml+exi"/>
      <representation mediaType="application/senml+xml"/>
      <representation mediaType="application/senml+json"/>
    </response>
    <response status="2.05">
      <representation mediaType="text/plain"/>

  <representation mediaType="application/senml+exi"/>
      <representation mediaType="application/senml+xml"/>
      <representation mediaType="application/senml+json"/>
    </response>
  </method>

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  <method id="observe" name="GET">
    <doc>Observe the CoAP Observation mechanism
   [I-D.ietf-core-observe] MAY be used to observe any changes in a
   resource, and receive asynchronous notifications as a result.  In
   addition, a set value of query string parameters are defined here to allow a client to control how often a client is interested in receiving
   notifications and how much sensor, an actuator or a resource value should change for the new
   representation to be interesting.  These query parameters are
   described in parameter.
     Only CoAP supports this method since it requires the following table.  A resource using an interface
   description defined CoRE
     Observe mechanism.</doc>
    <request>
      <param name="observe" style="header" type="xsd:integer">
        <option value = 0/>
      </param>
    </request>
    <response status="2.05">
      <representation mediaType="text/plain"/>
      <representation mediaType="application/senml+exi"/>
      <representation mediaType="application/senml+xml"/>
      <representation mediaType="application/senml+json"/>
    </response>
  </method>

  <method id="observe-cancel" name="GET">
    <doc>Cancel observation in progress.
     Only CoAP supports this specification and marked as Observable in
   its link description SHOULD support these observation parameters.
   The Change Step method since it requires the CoRE
     Observe mechanism.</doc>
    <request>
      <param name="observe" style="header" type="xsd:integer">
        <option value = 1/>
      </param>
    </request>
    <response status="2.05">
      <representation mediaType="text/plain"/>
      <representation mediaType="application/senml+exi"/>
      <representation mediaType="application/senml+xml"/>
      <representation mediaType="application/senml+json"/>
    </response>
  </method>

  <method id="update" name="PUT">
    <doc>Control the actuator or update a parameter can only be supported on resources with an
   atomic numeric value.

   These query parameters MUST be treated as resources that are read
   using GET a new value
    or command. Both HTTP and set using PUT, CoAP support this method.</doc>
    <request>
      <representation mediaType="text/plain"/>
      <representation mediaType="application/senml+exi"/>
      <representation mediaType="application/senml+xml"/>
      <representation mediaType="application/senml+json"/>
    </request>
    <response status="200"/>
    <response status="2.04"/>
  </method>

  <method id="getattr" name="GET">

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    <doc>Retrieve the observe attributes associated with a resource.
        Both HTTP and CoAP support this method.</doc>
    <request>
      <doc>This request MUST NOT be included in the Observe
   request.  Multiple parameters MAY be set at contain an Accept option with
      application/link-format when the same time by
   including resource supports
      other GET methods.</doc>
      <representation mediaType="application/link-format"/>
    </request>
    <response status="200">
      <representation mediaType="application/link-format"/>
    </response>
    <response status="2.05">
      <representation mediaType="application/link-format"/>
    </response>
  </method>

  <method id="setattr" name="PUT">
    <doc>Set the values in the query string of a PUT.  Before being set,
   these parameters have no default value.

         +----------------+------------------+------------------+
         | Resource       | Parameter        | Data Format      |
         +----------------+------------------+------------------+
         | Minimum Period | /{resource}?pmin | xsd:integer (>0) |
         | Maximum Period | /{resource}?pmax | xsd:integer (>0) |
         | Change Step    | /{resource}?st   | xsd:decimal (>0) |
         | Less Than      | /{resource}?lt   | xsd:decimal      |
         | Greater Than   | /{resource}?gt   | xsd:decimal      |
         +----------------+------------------+------------------+

   Minimum Period:  When present, some or all of the minimum period indicates observe attributes
    associated with a resource.
    Both HTTP and CoAP support this method.</doc>
    <request>
      <param name="pmin" style="query" type="xsd:integer"/>
      <param name="pmax" style="query" type="xsd:integer"/>
      <param name="lt" style="query" type="xsd:decimal"/>
      <param name="gt" style="query" type="xsd:decimal"/>
      <param name="st" style="query" type="xsd:decimal"/>
    </request>
    <response status="200">
    </response>
    <response status="2.04">
    </response>
  </method>

  <method id="apply" name="POST">
    <doc>Apply the
      minimum time value, if supplied, to wait (in seconds) before sending resources. Both HTTP and CoAP
    support this method.</doc>
    <request>
      <doc>The apply function may contain a new
      synchronization message (even if it has changed).  In payload to be applied.</doc>
    </request>
    <response status="200"/>
    <response status="2.04"/>
  </method>

  <method id="listLinks" name="GET">
    <doc>Retrieve the absence list of Web links associated to a resource.
     Both HTTP and CoAP support this parameter, method.</doc>
    <request>
    <doc>This request MUST contain an Accept option with

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    application/link-format when the minimum period resource supports
    other GET methods.</doc>
    </request>
    <response status="200">
      <representation mediaType="application/link-format"/>
    </response>
    <response status="2.05">
      <representation mediaType="application/link-format"/>
    </response>
  </method>

  <method id="appendLinks" name="POST">
    <doc>Append new Web links to a resource which is up a collection
    of links. Both HTTP and CoAP support this method.</doc>
    <request>
      <representation mediaType="application/link-format"/>
    </request>
    <response status="200"/>
    <response status="2.04"/>
  </method>

  <method id="clearLinks" name="DELETE">
    <doc>Clear all Web Links in a resource which is a collection
    of links. Both HTTP and CoAP support this method.</doc>
    <request>
    </request>
    <response status="200"/>
    <response status="2.02"/>
  </method>

  <method id="updateLinks" name="PATCH">
    <doc>Update all Web Links in a resource which is a collection
    of links. Both HTTP and CoAP support this method.</doc>
    <doc>This request MUST contain a Content-Format option with
    application/merge-patch+json.</doc>
    <request>
    </request>
    <response status="200"/>
    <response status="2.04"/>
  </method>

    <method id="addItem" name="POST">
    <doc>Add zero or more items to the notifier.

   Maximum Period:  When present, the maximum period indicates the
      maximum time collection with their links. Both HTTP and CoAP support this method.</doc>
    <doc>This request MAY contain a Content-Format option with
    application/collection+senml+json.</doc>
    <doc>This request MAY contain a Content-Format option with
    application/senml+json.</doc>
    <request>

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    </request>
    <response status="200"/>
    <response status="2.01"/>
  </method>

    <method id="readCollection" name="GET">
    <doc>REturn a representation of both links and items in seconds between two consecutive syncronization
      messages (regardless if it has changed).  In the absence of collection. Both HTTP and CoAP support this
      parameter, the maximum period is up to the notifier.  The maximum
      period method.</doc>
    <doc>This request MUST be greater than the minimum period parameter (if
      present).

   Change Step:  When present, the change step indicates contain an Accepts option with
    application/collection+senml+json.</doc>
   <request>
    </request>
    <response status="200"/>
    <response status="2.05"/>
  </method>

</application>

7.  Function Sets and Profiles

   This section defines how much the
      value of a resource SHOULD change before sending set of REST resources can be created
   called a new
      notification (compared function set.  A Function Set is similar to a function block
   in the value sense that it consists of the last notification).
      This parameter has lower priority than the period parameters, thus
      even if the change step has been fulfilled, the time since the
      last notification SHOULD be between pmin input, output and pmax.

   Greater Than:  When present, Greater Than indicates the upper limit
      value the resource value SHOULD cross before sending a new
      notification.  This parameter has lower priority than the period
      parameters, thus even if the Greater Than limit has been crossed,
      the time since the last notification SHOULD be between pmin
   resources and
      pmax.

   Less Than:  When present, Less Than indicates the lower limit value
      the resource value SHOULD cross before sending a new notification.
      This parameter has lower priority than the period parameters, thus
      even if the Less Than limit has been crossed, the time since the
      last notification SHOULD be between pmin contains internal logic.  A Function Set can have a
   subset of mandatory inputs, outputs and pmax.

5.10.  Future Interfaces parameters to provide minimum
   interoperability.  It can also be extended with manufacturer/user-
   specific resources.  A device is expected that further interface descriptions will composed of one or more Function Set
   instances.

   An example of function sets can be defined in
   this and other specifications.  Potential found from the CoRE Resource
   Directory specification that defines REST interfaces to be considered for this specifications include:

   Collection:  This resource would be
   registration, group and lookup [I-D.ietf-core-resource-directory].
   The OMA Lightweight M2M standard [REF] also defines a container function set
   structure called an Objects that allows sub-
      resources to use integer path, instance and
   resource URI segments.  OMA Objects can be added or removed.

5.11.  WADL Description defined and then
   registered with an OMA maintained registry [REF].  This section defines is
   simply meant as a guideline for the formal Web Application Description Langauge
   (WADL) definition of these CoRE interface descriptions.

   <?xml version="1.0" standalone="yes"?>
   <application xmlns="http://research.sun.com/wadl/2006/10"
                xmlns:xsd="http://www.w3.org/2001/XMLSchema"
                xmlns:senml="urn:ietf:params:xml:ns:senml">

     <grammars>
       <include href="http://tools.ietf.org/html/draft-jennings-senml"/>
     </grammars>

     <doc title="CoRE Interfaces"/>

     <resource_type id="s">
       <doc title="Sensor resource type"/>
       <method href="#read"/>
       <method href="#observe"/>
       <method href="#observe-cancel"/>
       <method href="#getattr"/>
       <method href="#setattr"/>
     </resource_type>

     <resource_type id="p">
       <doc title="Parameter resource type"/>
       <method href="#read"/>
       <method href="#observe"/>
       <method href="#observe-cancel"/>
       <method href="#getattr"/>
       <method href="#setattr"/>
       <method href="#update"/>
     </resource_type>

     <resource_type id="rp">
       <doc title="Read-only Parameter resource type"/>
       <method href="#read"/>
       <method href="#observe"/>
       <method href="#observe-cancel"/>
       <method href="#getattr"/>
       <method href="#setattr"/>
     </resource_type>

     <resource_type id="a">
       <doc title="Actuator resource type"/>
       <method href="#read"/>
       <method href="#observe"/>
       <method href="#observe-cancel"/>
       <method href="#getattr"/>
       <method href="#setattr"/>
       <method href="#update"/>
       <method href="#toggle"/>
     </resource_type>
     <resource_type id="ll">
       <doc title="Link List type"/></doc>
       <method href="#listLinks"/>
     </resource_type>

     <resource_type id="b">
       <doc title="Batch other such REST
   interfaces, either custom or part of other specifications.

7.1.  Defining a Function Set

   In a Function Set, types of sub-resources type">The methods read,
        observe, update and toggle resources are applied to each sub-
        resource of defined.  Each type
   includes a human readable name, a path template, a Resource Type for
   discovery, the requested resource that supports it. Mixed Interface Definition and the data type and allowed
   values.  A Function Set definition may also include a field
   indicating if a sub-resource types can be supported.</doc>
       <method href="#read"/>
       <method href="#observe"/>
       <method href="#observe-cancel"/>
       <method href="#getattr"/>
       <method href="#setattr"/>
       <method href="#update"/>
       <method href="#toggle"/>
       <method href="#listLinks"/>
     </resource_type>

     <resource_type id="lb">
       <doc title="Linked Batch is mandatory or optional.

Internet-DrafReusable Interface Definitions for Constrained October 2015

7.1.1.  Path template

   A Function Set is a container resource type">. The methods read,
        obervableRead, update and toggle under which its sub-resources
   are applied organized.  The profile defines the path to each linked resource of a
   Function Set in a path template.  The template can contain either
   relative paths or absolute paths depending on the requested resource that supports it. Mixed
        linked resource types profile needs.  An
   absolute Function Set should be located at its recommended root path
   on a web server, however it can be supported.</doc>
       <method href="#read"/>
       <method href="#observe"/>
       <method href="#observe-cancel"/>
       <method href="#getattr"/>
       <method href="#setattr"/>
       <method href="#update"/>
       <method href="#listLinks"/>
       <method href="#appendLinks"/>
       <method href="#clearLinks"/>
     </resource_type>

     <resource_type id="bnd">
       <doc title="Binding table resource type">A modifiable list located under an alternative path
   if necessary (for example multi-purpose devices, gateways etc.).  A
   relative Function Set can be instantiated as many times as needed on
   a web server with an arbitrary root path.  However some Function Sets
   (e.g. device description) only make sense as singletons.

   The path template includes a possible index {#} parameter, and
   possible fixed path segments.  The index {#} allows for multiple
   instances of
       links. Each link MUST have the relation this type "boundTo".</doc>
       <method href="#listLinks"/>
       <method href="#appendLinks"/>
       <method href="#clearLinks"/>
     </resource_type>

     <method id="read" name="GET">
       <doc>Retrieve of resource, and can be any string.  The root
   path and the value indexes are the only variable elements in a path
   template.  All other path segments should be fixed.

7.1.2.  Resource Type

   Each root resource of a sensor, an actuator or Function Set is assigned a parameter.
        Both HTTP and CoAP support this method.</doc>
       <request>
       </request>
       <response status="200">
         <representation mediaType="text/plain"/>
         <representation mediaType="application/senml+exi"/>
         <representation mediaType="application/senml+xml"/>
         <representation mediaType="application/senml+json"/>
       </response>
       <response status="2.05">
         <representation mediaType="text/plain"/>

     <representation mediaType="application/senml+exi"/>
         <representation mediaType="application/senml+xml"/>
         <representation mediaType="application/senml+json"/>
       </response>
     </method>

     <method id="observe" name="GET">
       <doc>Observe the value Resource Type
   parameter, therefore making it possible to discover it.  Each sub-
   resource of a sensor, an actuator or Function Set is also assigned a Resource Type
   parameter.
        Only CoAP supports this method since it requires the CoRE
        Observe mechanism.</doc>
       <request>
         <param name="observe" style="header" type="xsd:integer">
           <option value = 0/>
         </param>
       </request>
       <response status="2.05">
         <representation mediaType="text/plain"/>
         <representation mediaType="application/senml+exi"/>
         <representation mediaType="application/senml+xml"/>
         <representation mediaType="application/senml+json"/>
       </response>
     </method>

     <method id="observe-cancel" name="GET">
       <doc>Cancel observation in progress.
        Only CoAP supports this method since it requires the CoRE
        Observe mechanism.</doc>
       <request>
         <param name="observe" style="header" type="xsd:integer">
           <option value = 1/>
         </param>
       </request>
       <response status="2.05">
         <representation mediaType="text/plain"/>
         <representation mediaType="application/senml+exi"/>
         <representation mediaType="application/senml+xml"/>
         <representation mediaType="application/senml+json"/>
       </response>

     </method>

     <method id="update" name="PUT">
       <doc>Control the actuator or update  This Resource Type is used for resource discovery and is
   usually necessary to discover optional resources supported on a
   specific device.  The Resource Type of a Function Set may also be
   used for service discovery and can be exported to DNS-SD [RFC6763]
   for example.

   The Resource Type parameter with a new defines the value
       or command. Both HTTP and CoAP support that should be included
   in the rt= field of the CoRE Link Format when describing a link to
   this method.</doc>
       <request>
         <representation mediaType="text/plain"/>
         <representation mediaType="application/senml+exi"/>
         <representation mediaType="application/senml+xml"/>
         <representation mediaType="application/senml+json"/>
       </request>
       <response status="200"/>
       <response status="2.04"/>
     </method>

     <method id="getattr" name="GET">
       <doc>Retrieve resource.  The value SHOULD be in the observe attributes associated form "namespace.type" for
   root resources and "namespace.type.subtype" for sub-resources.  This
   naming convention facilitates resource type filtering with a the
   /.well-known/core resource.
           Both HTTP  However a profile could allow mixing in
   foreign namespace references within a Function Set to import external
   references from other object models (e.g.  SenML and CoAP support UCUM).

7.1.3.  Interface Description

   The Interface Description parameter defines the REST interface for
   that type of resource.  Several base interfaces are defined in
   Section 6 of this method.</doc>
       <request>
         <doc>This request MUST contain an Accept option with
         application/link-format when document.  For a given profile, the Interface
   Description may be inferred from the Resource Type.  In that case the
   Interface Description MAY be elided from link descriptions of
   resource supports
         other GET methods.</doc>
         <representation mediaType="application/link-format"/>
       </request>
       <response status="200">
         <representation mediaType="application/link-format"/>
       </response>
       <response status="2.05">
         <representation mediaType="application/link-format"/>
       </response>
     </method>

     <method id="setattr" name="PUT">
       <doc>Set types defined in the profile, but should be included for
   custom extensions to the profile.

Internet-DrafReusable Interface Definitions for Constrained October 2015

   The root resource of a Function Set should provide a list of links to
   its sub-resources in order to offer gradual reveal of resources.  The
   CoRE Link List interface defined in Section 6.1 offers this
   functionality so a root resource should support this interface or a
   derived interface like CoRE Batch (See Section 6.2).

7.1.4.  Data type

   The Data Type field defines the values type of some value (and possible range)
   that is returned in response to a GET for that resource or all of the observe attributes
       associated accepted
   with a resource.
       Both HTTP PUT.  The interfaces defined in Section 6 make use of plain
   text and CoAP support this method.</doc>
       <request>
         <param name="pmin" style="query" type="xsd:integer"/>
         <param name="pmax" style="query" type="xsd:integer"/>
         <param name="lt" style="query" type="xsd:decimal"/>
         <param name="gt" style="query" type="xsd:decimal"/>
         <param name="st" style="query" type="xsd:decimal"/>
       </request>
       <response status="200">
       </response>
       <response status="2.04">
       </response>
     </method>
     <method id="toggle" name="POST">
       <doc>Toggle SenML Media types for the values actual format of actuator resources. Both HTTP and CoAP
       support this method.</doc>
       <request>
         <doc>The toggle function is only applicable if the request
         is empty.</doc>
       </request>
       <response status="200"/>
       <response status="2.04"/>
     </method>

     <method id="listLinks" name="GET">
       <doc>Retrieve data.  A
   profile may restrict the list of Web supported content formats for the
   CoRE interfaces or define new interfaces with new content types.

7.2.  Discovery

   A device conforming to a profile SHOULD make its resources
   discoverable by providing links associated to the resources on the path /.well-
   known/core as defined in [RFC6690].  All resources hosted on a resource.
        Both HTTP and CoAP support this method.</doc>
       <request>
       <doc>This request MUST contain an Accept option device
   SHOULD be discoverable either with
       application/link-format when the resource supports
       other GET methods.</doc>
       </request>
       <response status="200">
         <representation mediaType="application/link-format"/>
       </response>
       <response status="2.05">
         <representation mediaType="application/link-format"/>
       </response>
     </method>

     <method id="appendLinks" name="POST">
       <doc>Append new Web a direct link in /.well-known/core
   or by following successive links starting from /.well-known/core.

   The root path of a Function Set instance SHOULD be directly
   referenced in /.well-known/core in order to a resource which is a collection offer discovery at the
   first discovery stage.  A device with more than 10 individual
   resources SHOULD only expose Function Set instances in /.well-known/
   core to limit the size of links. Both HTTP and CoAP support this method.</doc>
       <request>
         <representation mediaType="application/link-format"/>
       </request>
       <response status="200"/>
       <response status="2.04"/>
     </method>

     <method id="clearLinks" name="DELETE">
       <doc>Clear all Web Links resource.

   In addition, a device MAY register its resources to a Resource
   Directory using the registration interface defined in
   [I-D.ietf-core-resource-directory] if such a resource which directory is available.

7.3.  Versioning

   A profile should track Function Set changes to avoid incompatibility
   issues.  Evolutions in a collection
       of links. Both HTTP and CoAP support this method.</doc>
       <request>
       </request>
       <response status="200"/>
       <response status="2.04"/>
     </method>

   </application>

6. Function Set SHOULD be backward compatible.

8.  Security Considerations

   An implementation of a client needs to be prepared to deal with
   responses to a request that differ from what is specified in this
   document.  A server implementing what the client thinks is a resource
   with one of these interface descriptions could return malformed
   representations and response codes either by accident or maliciously.
   A server sending maliciously malformed responses could attempt to
   take advantage of a poorly implemented client for example to crash
   the node or perform denial of service.

7.

Internet-DrafReusable Interface Definitions for Constrained October 2015

9.  IANA Considerations

   The interface description types defined require registration.

   The new link relation relations type "boundto" requires and "grp" require registration.

8.

10.  Acknowledgments

   Acknowledgement is given to colleagues from the SENSEI project who
   were critical in the initial development of the well-known REST
   interface concept, to members of the IPSO Alliance where further
   requirements for interface types have been discussed, and to Szymon
   Sasin, Cedric Chauvenet, Daniel Gavelle and Carsten Bormann who have
   provided useful discussion and input to the concepts in this
   document.

9.

11.  Changelog

   Changes from -03 to -04

   o  Fixed tickets #385 and #386

   o  Changed abstract and into to better describe content

   o  Focus on Interface and not function set/profiles in intro

   o  Changed references from draft-core-observe to RFC7641

   o  Moved Function sets and Profiles to section after Interfaces

   o  Moved Observe Attributes to the Link Binding section

   o  Add a Collection section to describe the collection types

   o  Add the Hypermedia Collection Interface Description

   Changes from -02 to -03

   o  Added lt and gt to binding format section.

   o  Added pmin and pmax observe parameters to Observation Attributes

   o  Changed the definition of lt and gt to limit crossing.

   o  Added definitions for getattr and setattr to WADL.

   o  Added getattr and setattr to observable interfaces.

Internet-DrafReusable Interface Definitions for Constrained October 2015

   o  Removed query parameters from Observe definition.

   o  Added observe-cancel definition to WADL and to observable
      interfaces.

   Changes from -01 to -02

   o  Updated the date and version, fixed references.

   o  Removed pmin and pmax observe parameters [Ticket #336]

   Changes from -00 to WG Document -01

   o  Improvements to the Function Set section.

   Changes from -05 to WG Document -00

   o  Updated the date and version.

   Changes from -04 to -05

   o  Made the Observation control parameters to be treated as resources
      rather than Observe query parameters.  Added Less Than and Greater
      Than parameters.

   Changes from -03 to -04

   o  Draft refresh

   Changes from -02 to -03

   o  Added Bindings

   o  Updated all rt= and if= for the new Link Format IANA rules

   Changes from -01 to -02

   o  Defined a Function Set and its guidelines.

   o  Added the Link List interface.

   o  Added the Linked Batch interface.

   o  Improved the WADL interface definition.

   o  Added a simple profile example.

10.

Internet-DrafReusable Interface Definitions for Constrained October 2015

12.  References
10.1.

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997. 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988,
              DOI 10.17487/RFC5988, October 2010. 2010,
              <http://www.rfc-editor.org/info/rfc5988>.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012.

10.2. 2012,
              <http://www.rfc-editor.org/info/rfc6690>.

12.2.  Informative References

   [I-D.ietf-core-observe]
              Hartke, K., "Observing Resources in CoAP",
              draft-ietf-core-observe-16 (work in progress),
              December 2014.

   [I-D.ietf-core-resource-directory]
              Shelby, Z., Koster, M., Bormann, C., and P. Stok, "CoRE
              Resource Directory", draft-ietf-core-resource-directory-03 draft-ietf-core-resource-directory-04
              (work in progress), June July 2015.

   [I-D.jennings-core-senml]
              Jennings, C., Shelby, Z., Arkko, J., and A. Keranen,
              "Media Types for Sensor Markup Language (SENML)", draft-
              jennings-core-senml-01 (work in progress), July 2015.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013. 2013,
              <http://www.rfc-editor.org/info/rfc6763>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014. 2014,
              <http://www.rfc-editor.org/info/rfc7252>.

   [RFC7396]  Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
              DOI 10.17487/RFC7396, October 2014,
              <http://www.rfc-editor.org/info/rfc7396>.

Internet-DrafReusable Interface Definitions for Constrained October 2015

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)", RFC 7641,
              DOI 10.17487/RFC7641, September 2015,
              <http://www.rfc-editor.org/info/rfc7641>.

Appendix A.  Profile example

   The following is a short definition of simple profile.  This
   simplistic profile is for use in the examples of this document.

         +--------------------+-----------+------------+---------+
         |       Function Set | Root Path | RT         | IF      |
         +--------------------+-----------+------------+---------+
         | Device Description | /d        | simple.dev | core.ll |
         |            Sensors | /s        | simple.sen | core.b  |
         |          Actuators | /a        | simple.act | core.b  |
         +--------------------+-----------+------------+---------+

                           List of Function Sets

       +-------+----------+----------------+---------+------------+
       |  Type | Path     | RT             | IF      | Data Type  |
       +-------+----------+----------------+---------+------------+
       |  Name | /d/name  | simple.dev.n   | core.p  | xsd:string |
       | Model | /d/model | simple.dev.mdl | core.rp | xsd:string |
       +-------+----------+----------------+---------+------------+

                      Device Description Function Set

   +-------------+-------------+----------------+--------+-------------+
   |        Type | Path        | RT             | IF     | Data Type   |
   +-------------+-------------+----------------+--------+-------------+
   |       Light | /s/light    | simple.sen.lt  | core.s | xsd:decimal |
   |             |             |                |        | (lux)       |
   |    Humidity | /s/humidity | simple.sen.hum | core.s | xsd:decimal |
   |             |             |                |        | (%RH)       |
   | Temperature | /s/temp     | simple.sen.tmp | core.s | xsd:decimal |
   |             |             |                |        | (degC)      |
   +-------------+-------------+----------------+--------+-------------+

                           Sensors Function Set

Internet-DrafReusable Interface Definitions for Constrained October 2015

       +------+------------+----------------+--------+-------------+
       | Type | Path       | RT             | IF     | Data Type   |
       +------+------------+----------------+--------+-------------+
       |  LED | /a/{#}/led | simple.act.led | core.a | xsd:boolean |
       +------+------------+----------------+--------+-------------+

                          Actuators Function Set

Authors' Addresses

   Zach Shelby
   ARM
   150 Rose Orchard
   San Jose  95134
   FINLAND

   Phone: +1-408-203-9434
   Email: zach.shelby@arm.com

   Matthieu Vial
   Schneider-Electric
   Grenoble,
   Grenoble
   FRANCE

   Phone: +33 (0)47657 6522
   Email: matthieu.vial@schneider-electric.com

   Michael Koster
   ARM
   150 Rose Orchard
   San Jose  95134
   FINLAND

   Phone:
   USA

   Email: michael.koster@arm.com