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Network Working Group                                           E. Wilde
Internet-Draft                                           CA Technologies
Intended status: Informational                            March 13, 2017
Expires: September 14, 2017


                  Link Relation Types for Web Services
                    draft-wilde-service-link-rel-03

Abstract

   Many resources provided on the Web are part of sets of resources that
   are provided in a context that is managed by one particular service
   provider.  Often, these sets of resources are referred to as "Web
   Services" or "Web APIs".  This specification defines link relations
   for representing relationships from those resources to ones that
   provide documentation or descriptions of the Web services.  The
   difference between these concepts is that documentation is primarily
   intended for human consumers, whereas descriptions are primarily
   intended for automated consumers.  It also defines a link relation to
   identify a status resource that is used to represent operational
   information about a service's status.

Note to Readers

   Please discuss this draft on the ART mailing list
   (<https://www.ietf.org/mailman/listinfo/art>).

   Online access to all versions and files is available on GitHub
   (<https://github.com/dret/I-D/tree/master/service-link-rel>).

Status of 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
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   This Internet-Draft will expire on September 14, 2017.




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Copyright Notice

   Copyright (c) 2017 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
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Web Services  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Documenting Web Services  . . . . . . . . . . . . . . . .   4
     3.2.  Describing Web Services . . . . . . . . . . . . . . . . .   5
     3.3.  Unified Documentation/Description . . . . . . . . . . . .   5
   4.  Link Relations for Web Services . . . . . . . . . . . . . . .   5
     4.1.  The service-doc Link Relation Type  . . . . . . . . . . .   5
     4.2.  The service-desc Link Relation Type . . . . . . . . . . .   6
   5.  Web Service Status Resources  . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Link Relation Type: service-doc . . . . . . . . . . . . .   6
     6.2.  Link Relation Type: service-desc  . . . . . . . . . . . .   7
     6.3.  Link Relation Type: status  . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   One of the defining aspects of the Web is that it is possible to
   interact with Web resources without any prior knowledge of the
   specifics of the resource.  Following Web Architecture
   [W3C.REC-webarch-20041215] by using URIs, HTTP, and media types, the
   Web's uniform interface allows interactions with resources without
   the more complex binding procedures of other approaches.





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   Many resources on the Web are provided as part of a set of resources
   that are referred to as a "Web Service" or a "Web API".  In many
   cases, these services or APIs are defined and managed as a whole, and
   it may be desirable for clients to be able to discover this service
   information.

   Service information can be broadly separated into two categories: One
   category is primarily targeted for human users and often uses generic
   representations for human readable documents, such as HTML or PDF.
   The other category is structured information that follows some more
   formalized description model, and is primarily intended for
   consumption by machines, for example for tools and code libraries.

   In the context of this memo, the human-oriented variant is referred
   to as "documentation", and the machine-oriented variant is referred
   to as "description".

   These two categories are not necessarily mutually exclusive, as there
   are representations that have been proposed that are intended for
   both human consumption, and for interpretation by machine clients.
   In addition, a typical pattern for service documentation/description
   is that there is human-oriented high-level documentation that is
   intended to put a service in context and explain the general model,
   which is complemented by a machine-level description that is intended
   as a detailed technical description of the service.  These two
   resources could be interlinked, but since they are intended for
   different audiences, it can make sense to provide entry points for
   both of them.

   This memo places no constraints on the specific representations used
   for either of those two categories.  It simply allows providers of a
   Web service to make the documentation and/or the description of their
   services discoverable, and defines two link relations that serve that
   purpose.

   In addition, this memo defines a link relation that allows providers
   of a Web service to link to a resource that represents status
   information about the service.  This information often represents
   operational information that allows service consumers to retrieve
   information about "service health" and related issues.

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 RFC 2119 [RFC2119].





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3.  Web Services

   "Web Services" or "Web APIs" (sometimes also referred to as "HTTP
   API" or "REST API") are a way to expose information and services on
   the Web. Following the principles of Web architecture
   [W3C.REC-webarch-20041215], they expose URI-identified resources,
   which are then accessed and transferred using a specific
   representation.  Many services use representations that contain
   links, and often these links are typed links.

   Using typed links, resources can identify relationship types to other
   resources.  RFC 5988 [RFC5988] establishes a framework of registered
   link relation types, which are identified by simple strings and
   registered in an IANA registry.  Any resource that supports typed
   links according to RFC 5988 can then use these identifiers to
   represent resource relationships on the Web without having to re-
   invent registered relation types.

   In recent years, Web services as well as their documentation and
   description languages have gained popularity, due to the general
   popularity of the Web as a platform for providing information and
   services.  However, the design of documentation and description
   languages varies with a number of factors, such as the general
   application domain, the preferred application data model, and the
   preferred approach for exposing services.

   This specification allows service providers to use a unified way to
   link to service documentation and/or description.  This link should
   not make any assumptions about the provided type of documentation
   and/or description, so that service providers can choose the ones
   that best fit their services and needs.

3.1.  Documenting Web Services

   In the context of this specification, "documentation" refers to
   information that is primarily intended for human consumption.
   Typical representations for this kind of documentation are HTML and
   PDF.

   Documentation is often structured, but the exact kind of structure
   depends on the structure of the service that is documented, as well
   as on the specific way in which the documentation authors choose to
   document it.








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3.2.  Describing Web Services

   In the context of this specification, "description" refers to
   information that is primarily intended for machine consumption.
   Typical representations for this are dictated by the technology
   underlying the service itself, which means that in today's technology
   landscape, description formats exist that are based on XML, JSON,
   RDF, and a variety of other structured data models.  Also, in each of
   those technologies, there may be a variety of languages that are
   defined to achieve the same general purpose of describing a Web
   service.

   Descriptions are always structured, but the structuring principles
   depend on the nature of the described service.  For example, one of
   the earlier service description approaches, the Web Services
   Description Language (WSDL), uses "operations" as its core concept,
   which are essentially identical to function calls, because the
   underlying model is based on that of the Remote Procedure Call (RPC)
   model.  Other description languages for non-RPC approaches to
   services will use different structuring approaches.

3.3.  Unified Documentation/Description

   If service providers use an approach where there is no distinction of
   service documentation Section 3.1 and service description
   Section 3.2, then they may not feel the need to use two separate
   links.  In such a case, an alternative approach is to use the
   "service" link relation type, which has no indication of whether it
   links to documentation or description, and thus may be better fit if
   no such differentiation is required.

4.  Link Relations for Web Services

   In order to allow Web services to represent the relation of
   individual resources to service documentation or description, this
   specification introduces and registers two new link relation types.

4.1.  The service-doc Link Relation Type

   The "service-doc" link relation type is used to represent the fact
   that a resource is part of a bigger set of resources that are
   documented at a specific URI.  The target resource is expected to
   provide documentation that is primarily intended for human
   consumption.







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4.2.  The service-desc Link Relation Type

   The "service-desc" link relation type is used to represent the fact
   that a resource is part of a bigger set of resources that are
   described at a specific URI.  The target resource is expected to
   provide a service description that is primarily intended for machine
   consumption.  In many cases, it is provided in a representation that
   is consumed by tools, code libraries, or similar components.

5.  Web Service Status Resources

   Web services providing access to a set of resources often are hosted
   and operated in an environment for which status information may be
   available.  This information may be as simple as confirming that a
   service is operational, or may provide additional information about
   different aspects of a service, and/or a history of status
   information, possibly listing incidents and their resolution.

   The "status" link relation type can be used to link to such a status
   resource, allowing service consumers to retrieve status information
   about a Web service's status.  Such a link may not be available from
   all resources provided by a Web service, but from key resources such
   as a Web service's home resource [I-D.nottingham-json-home].

   This memo does not restrict the representation of a status resource
   in any way.  It may be primarily focused on human or machine
   consumption, or a combination of both.  It may be a simple "traffic
   light" indicator for service health, or a more sophisticated
   representation conveying more detailed information such as service
   subsystems and/or a status history.

6.  IANA Considerations

   The link relation types below have been registered by IANA per
   Section 6.2.1 of RFC 5988 [RFC5988]:

6.1.  Link Relation Type: service-doc

      Relation Name: service-doc

      Description: Linking to service documentation that is primarily
      intended for human consumption.

      Reference: [[ This document ]]







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6.2.  Link Relation Type: service-desc

      Relation Name: service-desc

      Description: Linking to service description that is primarily
      intended for consumption by machines.

      Reference: [[ This document ]]

6.3.  Link Relation Type: status

      Relation Name: status

      Description: Linking to a resource that represents the status of a
      Web service or API.

      Reference: [[ This document ]]

7.  Security Considerations

   ...

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988, October 2010.

8.2.  Informative References

   [I-D.nottingham-json-home]
              Nottingham, M., "Home Documents for HTTP APIs", draft-
              nottingham-json-home-04 (work in progress), May 2016.

   [W3C.REC-webarch-20041215]
              Jacobs, I. and N. Walsh, "Architecture of the World Wide
              Web, Volume One", World Wide Web Consortium
              Recommendation REC-webarch-20041215, December 2004,
              <http://www.w3.org/TR/2004/REC-webarch-20041215>.

Appendix A.  Acknowledgements

   Thanks for comments and suggestions provided by Mike Amundsen, Oliver
   Gierke, Sebastien Lambla, and Darrell Miller.




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Author's Address

   Erik Wilde
   CA Technologies

   Email: erik.wilde@dret.net
   URI:   http://dret.net/netdret/












































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