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Network Working Group                                        A. Rezafard
Internet-Draft                                            Afilias Canada
Intended status: Informational                         November 17, 2008
Expires: May 21, 2009

      Extensible Supply-chain Discovery Service Problem Statement

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

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   This document discusses the requirements of an application layer
   protocol for Discovery Services.  Discovery Services at its core
   offers to authenticated and authorized users the means to discover
   resources of information for a particular identifier.  The
   information resource can be any data source which provides an
   interface on a network that allows for retrieval of the data.  An
   information resource could publish its network address (reference to
   the resource) to a Discovery Service coupled with an identifier.
   Then an authenticated and authorized user could query the Discovery
   Service with the same identifier to receive reference information to
   the resources.  Interfacing with the resources for actually
   retrieving the data is out of scope of Discovery Services; the role
   of Discovery Services is to enable a client to find the network
   addresses and types (e.g.  URLs) of information resources for a
   particular identifier of interest.

   This protocol is applicable to numerous scenarios such as track and
   trace in trade supply chains, where a number of independent resources
   may hold information about a particular object and may have an
   interest in selective sharing of that information, in order to
   improve the efficiency of the supply chain network.

   However, other applications can be envisaged, as a 'bottom-up' or
   'grassroots' way for generators of information content to: 1) declare
   that they have information or commentary on a particular topic or
   subject (which might be a physical object, geographic location or
   even an abstract concept) 2) specify a network address through which
   that content can be retrieved, 3) specify restrictions about the
   community of clients that are entitled to receive knowledge about the
   existence of their content or see the link.  This approach can be
   contrasted with the top-down approach of existing web search engines
   that rely on crawling/spidering of content that must be already
   posted in the public domain before it can be indexed - and where the
   link information is generally made publicly available in a manner
   that does not discriminate between clients on an individual basis.

   This document outlines a set of design concerns that an application
   layer protocol needs to address in order to be widely adopted and
   deployable on public networks

   This document obsoletes "Extensible Supply-chain Discovery Service
   Problem Statement draft-rezafard-esds-problem-statement-02".

   Comments are solicited and should be addressed to the mailing list at
   esds@ietf.org and/or the author(s).

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Introduction: Supply chain applications as one driver  . .  5
     1.2.  What is ESDS?  . . . . . . . . . . . . . . . . . . . . . .  6
     1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
     1.4.  Problem Statement  . . . . . . . . . . . . . . . . . . . .  7
     1.5.  Description  . . . . . . . . . . . . . . . . . . . . . . .  9
   2.  Internet Concerns  . . . . . . . . . . . . . . . . . . . . . . 10
     2.1.  Public Networks and Tree-Walking Concerns  . . . . . . . . 10
     2.2.  Bootstrapping Concerns . . . . . . . . . . . . . . . . . . 11
   3.  Other Standards  . . . . . . . . . . . . . . . . . . . . . . . 13
     3.1.  Object Naming Service (ONS)  . . . . . . . . . . . . . . . 13
     3.2.  EPC Information Services (EPCIS) . . . . . . . . . . . . . 13
     3.3.  Universal Description Discovery and Integration (UDDI) . . 13
     3.4.  Interface for Metadata Access Point (IF-MAP) . . . . . . . 14
   4.  Related Standards Development Organizations  . . . . . . . . . 16
   5.  Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     5.1.  Flow Diagrams  . . . . . . . . . . . . . . . . . . . . . . 17
     5.2.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 18
       5.2.1.  Access Control . . . . . . . . . . . . . . . . . . . . 18
     5.3.  Publish  . . . . . . . . . . . . . . . . . . . . . . . . . 19
     5.4.  Query  . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     5.5.  Relabel/Aggregation/Disaggregation . . . . . . . . . . . . 20
     5.6.  Multiple Organizations . . . . . . . . . . . . . . . . . . 21
     5.7.  Identifier Agnostic  . . . . . . . . . . . . . . . . . . . 21
       5.7.1.  Reusing Identifiers  . . . . . . . . . . . . . . . . . 22
     5.8.  Extensible . . . . . . . . . . . . . . . . . . . . . . . . 23
     5.9.  Policies . . . . . . . . . . . . . . . . . . . . . . . . . 23
     5.10. Stale Links  . . . . . . . . . . . . . . . . . . . . . . . 23
     5.11. Peer-to-Peer Communications  . . . . . . . . . . . . . . . 24
   6.  Technical Challenges . . . . . . . . . . . . . . . . . . . . . 26
     6.1.  Auditability . . . . . . . . . . . . . . . . . . . . . . . 26
     6.2.  Responsiveness . . . . . . . . . . . . . . . . . . . . . . 26
     6.3.  Availability . . . . . . . . . . . . . . . . . . . . . . . 26
   7.  Related Activities . . . . . . . . . . . . . . . . . . . . . . 27
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 29
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 30
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 31
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 32
     12.2. Informative References . . . . . . . . . . . . . . . . . . 32
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 34
   Intellectual Property and Copyright Statements . . . . . . . . . . 35

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1.  Introduction

   As the Internet applications become more and more service oriented
   and specialized, the demand for collaboration among these
   applications increases.  These applications can collaborate on
   services or on topics.  Open collaboration on services is already
   taking place via Universal Description Discovery and Integration
   (UDDI).  Selective collaboration on specific topics is the problem
   domain that Discovery Services aims to address.

   A first step towards collaboration among applications on topics would
   be to use a common identifier for each topic.  For example a topic
   can be something conceptual like the name of a book, or a topic can
   be a particular physical object with a serialized identifier.  The
   use of common identifiers will enable dispersed applications to
   inter-communicate with each other.  Note that it is not the role of
   Discovery Services to develop such common identifiers - this is left
   to existing standards such as URIs and semantic web initiatives such
   as the Dublin Core vocabulary.

   The second step for the applications would be to find other resources
   of information on a common topic.  This is made possible when an
   application advertizes that it holds information on a topic.  This is
   made possible by Discovery Services since an application can
   advertize to a Discovery Service that it holds information on a
   specific topic, by publishing a reference to resources that hold
   relative information on the topic of interest.

   At a conceptual level, Discovery Services can be superficially
   regarded as being somewhat analogous to a bottom-up 'search engine'
   for an 'Internet of things'.  However, there are some fundamental
   differences from the paradigm of public web search engines.  The
   serial-level information will usually be protected and will only be
   made available to authorized organizations, with whom the information
   provider has an established trust relationship.  For this reason, we
   cannot assume that Discovery Services will be able to automatically
   'spider' or 'crawl' the network to compile an index of links, since
   the underlying information may not be generally available.

   Instead, we assume that each information provider will be able to
   voluntarily publish a record or registration for a particular common
   identifier, in order that a link can be established back to them as a
   potential provider of information.  At the same time, also the 'link'
   information will be protected by access control policies defined by
   each information provider, as well as any policies that are imposed
   by the operator of a Discovery Service.  Unlike most public search
   engines, there may be little or no 'link' information provided to
   non-authenticated users or directly to the general public without

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   authentication, although in some specific applications, citizens may
   be provided with indirect access to traceability information that was
   gathered via an authorized authenticated actor, such as the retailer
   or manufacturer.

   This approach enables distributed management of collected information
   and allows each organization to restrict who can access the data;
   they can specify an access control policy (which is enforced by a
   Discovery Service) to limit visibility of the 'link' information -
   and additionally, they can specify and enforce an access control
   policy within their own information resource that holds the more
   detailed information.

1.1.  Introduction: Supply chain applications as one driver

   Currently, a number of industry sectors are moving towards improved
   track and trace systems by the use of Auto-ID technologies (such as
   Radio-Frequency Identification (RFID)) that improve the ability to
   automate collection of observations, as well as the use of unique
   identifiers for each individual object, to improve the granularity of
   information, so that it is possible to track not only at the
   granularity of batches or lots - but actually trace the entire life
   history of an individual object.  This is particularly important in
   the fight against counterfeiting and for assuring the traceability
   and authenticity of foods, pharmaceuticals and other safety-critical
   objects, such as aircraft and automotive parts.

   As well as automating the collection of such data, companies are also
   moving towards sharing and exchange of serial-level data (i.e. data
   about individually identifiable objects), in order to improve the
   efficiency of supply chains.  This involves greater use of machine-
   to-machine information exchange, using standard interfaces for
   queries and output formats and requiring less intervention by human
   operators (e.g. less exchanging of spreadsheets via e-mail or FTP).
   However, serial-level data is commercially sensitive, since it can
   reveal information about stock levels and volumes and flows of goods.
   For this reason, most companies insist on maintaining strict control
   over who is granted access to their data, including the links to
   their data repositories or information services.  The entire
   lifecycle information for an individual object therefore remains
   decentralized and fragmented across multiple actors in the supply
   chain or extended product lifecycle.  Discovery Services will provide
   secure referral services that can be queried with a unique ID and
   return to authenticated authorized clients a list of links to
   multiple information providers, who can then be queried for more
   detailed information about the individual object.

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1.2.  What is ESDS?

   ESDS is a protocol for infrastructure that enables track and trace
   applications as well as product lifecycle information systems to find
   multiple sources of information.  Using the links provided by
   Discovery Services, they can then attempt to gather complete
   information about an individual physical object.

   Several organizations may handle an individual object at different
   stages of its life - and each of these organizations may collect and
   store some information about each object.  This may include
   observations of where the object was seen, details of operations
   performed on the object, as well as measurements (e.g. temperature)
   of the object or its environment.

   Even two objects that are of the same product type and which were
   created in the same batch or lot may ultimately follow different
   paths throughout their lives and each might be handled by a
   completely different set of organizations.

   We DO believe that each organization should be able to keep control
   of the data that they collect and store - and should have the ability
   to determine how much of this information is made available to others
   - and with whom.  This can be achieved by requiring authentication of
   clients specifying fine-grained access control policies associated
   with the roles assigned to those authenticated clients.

   We DO NOT propose that ESDS should act as an aggregator of detailed

   Instead, ESDS is intended as a lightweight referral service, whose
   sole purpose is to help a client to find one or more sources of
   detailed information.  In practice, a query to an ESDS about an
   object ID should return to an authenticated client a list of URLs of
   information resources that hold the detailed information about that
   particular object.  The client will only receive the URLs to
   information resources that have authorized (e.g. via access control
   policies) the client to see their URL address for that specific
   object ID.  The client can then contact each of those information
   resources in order to request more detailed information.  This
   process is OUTSIDE the scope of ESDS and may be subject to further
   authentication and authorization checks bilaterally between the
   client and each individual information resource.

1.3.  Terminology

   There are three actors in this problem:

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   Client:  refers to an actor that seeks (sources of) information about
       an individual object (or topic).
   Resource:  refers to an actor that holds information about an
       individual object (or topic) and may choose to share (some of)
       that information with a client (under certain conditions).
   ESDS:  refers to an intermediary lookup service protocol that enables
       a client to obtain referral information to one or more resources.
   Publish:  refers to the act of writing to a intermediary lookup
       service, Resource reference (address) information coupled with an
       object (or topic) identifier.  The publishing actor, as the
       information owner, could define access control rules to restrict
       which clients (or client roles) are allowed to view the Resource
       reference (address) for a particular object (or topic).

   What emerges from combinations of these actors and their
   relationships are:
   Organization (Partner):  refers to a business entity, which can be
       comprised of client actors or Resource actors.
   Community (Supply chain):  refers to a group of member organizations
       (partners) that may be willing to share some information among

   Note that not all members of the community will share exactly the
   same access privileges; there can be different bilateral access
   privileges within a community.

   Each organization can define rules that restrict which clients shall
   be allowed to see the address of its resource as a potentially
   relevant resource for a particular object identifier (or topic).
   Note that in some situations, the overall access control policy may
   be the result of a combination of rules defined by one or more
   organizations, as well as rules defined at a community level.

   Access privileges as defined by a community and its member
   organizations are only applicable to the information published by
   ESDS.  Each Resource must take its own security measures to protect
   its data (hosted at the published network address) from unprivileged

1.4.  Problem Statement

   Information sharing between organizations is essential for all modern
   networked communities.  There is a strict set of business and
   technical requirements that must be observed in order to enable open
   sharing of information between organizations.

   There are resources and clients in each community.  Each resource
   wants to advertise its knowledge (data) to interested and authorized

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   clients.  Only deploying private networks to connect whole
   communities is no longer feasible, as the more efficient and
   economical means of connecting resources and clients is to use public
   network infrastructure.  Currently, many industrial inter-
   organizational track-and-trace initiatives are deployed on public
   networks and the information is routed through the Internet.  Because
   of this trend, it is highly desirable that a draft protocol should be
   developed.  An IETF process consensus would ensure that the adopted
   protocol conforms to the Internet's operational needs.

   A key principle of information sharing within a community is that
   data ownership must be respected.  This means that each organization
   can collect information within their own systems and is not required
   to route that information to any other organizations.  However, they
   can choose to share selected information with other trusted
   organizations.  This in turn means that the information about any
   individual object may be held by multiple resources in a community.
   Therefore a mechanism is needed in order to facilitate the gathering
   of this information.

   A key requirement is that information accessibility is fully
   controllable.  The confidential information must be secure and hidden
   from unauthorized clients and only visible to the intended clients in
   a community.  In order to establish trust and reputation with the
   participating resources, unauthorized clients need to be barred from
   viewing, eavesdropping, or deducing information or even being aware
   of the existence of another organization's involvement with a
   specific identifier, if the client is not authorized to be aware of
   this involvement.

   There must be a common set of data that all resources will offer
   (only to authorized clients).  This set must be defined and agreed
   upon in the final protocol.  This set may include answers to who,
   what, when, where, and why as well as links to back-end systems.  An
   essential feature is for the protocol to be general-purpose and
   extensible to support multiple applications and uses beyond the needs
   of trade supply chains that motivated its initial development.

   Defining a bootstrapping procedure is a necessity when designing a
   global and autonomous network of systems.  Bootstrapping procedure
   would be the process of locating on the network, the appropriate
   Discovery Service(s) for a specific identifier.  Currently there are
   deployed supply chain systems that bootstrap via Internet's DNS
   roots.  One example of this is the EPCglobal Object Name Service
   [epc-object-naming-services] (ONS).  While ONS enables an economical
   means of bootstrapping, improper implementations may increase the
   traffic on DNS roots exponentially.  Since data will be routed
   through the Internet, the bootstrapping procedure needs to be

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   formulated under the IETF approval process.

1.5.  Description

   An Extensible Supply-chain Discovery Service (ESDS) provides a
   mechanism to locate one or more resources of information about a
   specific topic such as an individual physical object.  In a trade
   supply chain resources of information may include the original
   manufacturer or supplier of the object, as well as other
   organizations who have handled the object at some point during its
   lifecycle (including repair and maintenance organizations) and even
   organizations (such as customs or insurance agencies) who might hold
   information records related to the object, even though they may have
   never had physical custody of the object.

   This document defines the Problem Statement, Objectives and Technical
   Challenges related to the application layer protocol currently
   proposed as Extensible Supply-chain Discovery Services (ESDS).  ESDS
   enables the publishing and querying of referral links to information
   services that historical events related to specific objects with
   attached object identifiers.  The interface enables disparate
   applications to discovery resources of information and compile a
   consolidated view for an identifier.  Primarily, ESDS provides
   referral services in a loosely coupled mechanism with granular
   security that enables selective visibility.

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2.  Internet Concerns

2.1.  Public Networks and Tree-Walking Concerns

   Currently, another standards body, EPCglobal, has issued a related
   standard referred to as ONS [epc-object-naming-services].  ONS is
   effectively an extended version of DNS that does not benefit from the
   IETF review process and, in its design, necessitates increased tree-
   walking.  ONS specifies a reverse mapping of the EPCglobal "SGTIN"
   (one type of supply chain object identifier) as a hostname and allows
   for a reference (i.e.  URL) to a manufacturer's relevant back-end
   system (using a NAPTR record).  The SGTIN identifier is comprised of
   an EPC Manager Number, an Object Class, and a Serial Number.  The ONS
   lookup excludes the Serial Number portion of the SGTIN.  However, the
   ONS specification has already been extended in industry pilot
   projects to include the Serial Number, as this enables item level
   lookups for tagged objects in the supply chain.  Using serial level
   lookups, ONS could be used to indicate point to point referrals
   through the passage of a relevant identifier throughout the supply
   chain.  This would require successive updates to the hierarchal ONS
   to indicate incremental supply chain member referrals, reducing the
   effectiveness of caching.  Alternatively the ONS could provide a
   single, static point of referral to the first or initiating supply
   chain member.  However, even a relatively static entry, which only
   refers to the point of origin within the supply chain, would drive
   the number of public zone entries to extremely large numbers if an
   individual records were created for each serial number.  The number
   of records could exceed the current IPv4 address space by several
   orders of magnitude.  Also since many of the tagged physical objects
   would neither require nor provide network connectivity, utilizing
   IPv6 for such objects would waste this finite address space resource

   One common suggestion to manage this problem is to have multiple
   alternate ONS roots which can be managed for separate and unrelated
   supply chains and/or regions.  However, since there is nothing to
   prevent ONS from operating in the existing Internet root hierarchy,
   even alternate ONS providers can opt to drive traffic to the existing
   Internet root servers, rather than operate their own ONS roots.
   There has already been a pilot ONS implementation under the .aero
   zone (sgtin.id.ons.autoid.aero) where this phenomenon may already be

   It should be noted that ONS 1.0 [epc-object-naming-services]
   currently only specifies how to perform a lookup for a GTIN class
   identifier, which represents a product type.  It does not currently
   specify that ONS should be used for lookup of fully serialized
   identifiers.  While the number of GTIN codes may be a manageable

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   number, the potential number of serialized SGTIN identifiers is much
   larger.  Already in EPCglobal Tag Data Standards, the structure of
   SGTIN identifiers are defined such that it is theoretically possible
   to create in excess of 10^38 unique SGTIN identifiers for each GTIN
   code that is currently resolvable using ONS 1.0.  Already there are
   some companies who create over a billion objects per year for a
   single GTIN class.

   It was therefore a very wise decision of EPCglobal not to propose
   that ONS 1.0 should store a DNS record for each unique EPC, since the
   number of resulting DNS records could clearly overwhelm the DNS

   However, there is currently a missing element in the EPCglobal
   Network architecture, namely a search service that provides
   authorized authenticated clients with links to the multiple
   organizations who hold information about the unique life history of
   an individual object.  This missing element is essential for enabling
   robust track and trace applications.  Because this element
   ('Discovery Services') has not yet been defined, there is a danger
   that some organizations may misuse the ONS design and begin creating
   DNS records for each fully serialized object.  There is already one
   industry pilot where this is happening.  It is therefore essential
   that rapid progress should be made towards a protocol for Discovery
   Services that avoids placing such a burden on the DNS infrastructure.

   To summarize, there are two variations to the ONS specifications that
   can be observed in current deployments.  The first variation is an
   extension to the ONS structured hostname to include serialized level
   data (serialized SGTIN) instead of just the specified class data
   (GTIN class).  The second variance involves the tendency of the
   implementers to utilize the existing Internet root DNS servers
   instead of operating alternate ONS roots.  These variances could
   adversely affect the stability of the public network infrastructure.
   The IESG and IAB overview procedures at the IETF will ensure that the
   protocol and architecture proposed by the ESDS Work Group will be
   mindful of such deviations and take counter steps to prevent it.

2.2.  Bootstrapping Concerns

   The bootstrapping process enables an interested and authorized client
   to locate an object's Discovery Service server using only the
   information provided by the object identifier.  Unlike DNS, where
   there is a known set of root servers, ESDS will have numerous roots
   for various communities (supply chains) operating globally.  This, in
   turn, complicates the bootstrapping process.

   A common bootstrapping scenario would be exception handling in a

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   trade supply chain.  For example, if an object is mis-delivered, a
   recipient who has no pre-existing relationship to the trade supply
   chain, needs to obtain object ownership information and its
   corresponding Discovery Service server.  ESDS design must aim to
   accommodate this scenario while respecting privacy and security

   It has been suggested that ONS could be used for the bootstrapping
   process.  However, ONS-URN encoding and decoding scheme is only
   defined for EPC identifiers and ESDS is being architected to support
   non-EPC identifiers as well.  Also, ONS's hierarchical identifiers
   have raised privacy and security concerns by multiple participants in
   some Discovery Service scenarios.  While ONS can technically support
   multiple identifier schemes, with multiple issuing authorities, its
   hierarchical operation does depend on structured identifiers (for
   example, ManagerNumber.ObjectType.SerialNumber).  These identifiers
   display information about the object they are representing, such as
   type and manufacturer and as a result could compromise the privacy of
   an individual using the identifier.  Additionally, ONS has no
   authentication nor access control restricting who can query it.  ESDS
   must be designed for serial-level lookups and must support
   unstructured opaque identifiers to use as lookup keys within an ESDS
   service.  Because serial-level lookup information could potentially
   be subject to data mining by competitors, to reveal information about
   volumes and flows of goods, ESDS should fully support authentication
   and serial-level access controls to address concerns about privacy
   and confidentiality of data.

   To facilitate bootstrapping and exception handling scenarios ESDS
   design could investigate the use of peer-to-peer lookup protocols
   (such as JXTA [jxta-protocols]) as an alternative to hierarchical
   lookup protocols such as DNS and ONS.  This would keep the ESDS
   traffic flat and avoid walking up the Internet root hierarchy.  A
   major concern is that the bootstrapping design must not implicitly
   establish monopolies in the long run.  The IETF process will ensure
   that the resulting protocol design addresses the concerns of both the
   end-users and the network operators.

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3.  Other Standards

   Discovery Services address a problem domain that is not fully covered
   by any existing protocols.  Discovery Services enables authorized and
   authenticated users, to gather and retrieve links to resources of
   information about a topic or an object, this information is typically
   fragmented across multiple organizations and domains.  While there
   are related standards such as ONS, EPCIS, and UDDI, each of these
   address different problem statements and domains as follows:

3.1.  Object Naming Service (ONS)

   ONS is a mechanism that leverages the Domain Name System (DNS) to
   locate sources of authoritative information and related services
   about a product when queried using a hostname derived from the
   Electronic Product Code (EPC).  Its query interface as currently
   defined lacks access controls, authorization and authentication and
   this security deficiency makes it unsuitable for a Discovery Service
   handling commercially sensitive serial-level information.  The
   volumes of serial-level records generated by the supply chains would
   place an unreasonable burden on the DNS roots if ONS were mis-used
   for holding ONS records for each serial number.  However, Discovery
   Service can be used in collaboration with ONS to meet specific
   business requirements.  [epc-object-naming-services]

3.2.  EPC Information Services (EPCIS)

   EPCIS targets the sharing of data within an established network of
   trust and relationships.  Typically, a company can provide an EPCIS
   query interface to allow trusted organizations to retrieve some of
   its data.  It is not the role of EPCIS to enable robust linking to
   information across the entire supply chain or product lifecycle, nor
   to perform recursive 'proxy queries' to retrieve data from other
   parties, nor to facilitate exception handling and object
   bootstrapping across the whole supply chain.

3.3.  Universal Description Discovery and Integration (UDDI)

   UDDI is a standard for description and discovery of services and the
   functionality that they offer.  In contrast with UDDI, ESDS is
   concerned with locating services that provide information about a
   specific physical object; the ID of a physical object is the primary
   lookup key for ESDS, whereas UDDI is primarily queried for a
   particular type of service functionality desired.  Unlike UDDI
   registries, the data held within some Discovery Services may be much
   more commercially sensitive.  For example a supply chain Discovery
   Service, could reveal volumes and flows of goods in supply chains;

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   from a security and scalability perspective, ESDS therefore attempts
   to solve a more challenging problem than the problem that UDDI
   already solves.

3.4.  Interface for Metadata Access Point (IF-MAP)

   The protocol, IF-MAP, defines a simple publish/search/subscribe
   interface to the MAP.  The MAP is a common metadata database.  Within
   the MAP, metadata automatically aggregates with respect to common
   unique keys (i.e. identifiers).

   While IF-MAP's initial use-cases are in coordinated security, it was
   designed to meet other coordinated computing use-cases and may be
   appropriate for ESDS.  However, IF-MAP does not provide historical
   information (according to section 2.2 of the IF-MAP protocol).  A
   major use for ESDS is to maintain historical link information between
   the ID of a physical object (or a discussion topic or keyword) and
   multiple entities who have collected/ generated some information
   about that individual object (or discussion topic or keyword) at
   previous times.

   IF-MAP is concerned with building a graph to build associations
   between different identifiers and pieces of meta-data.  With ESDS,
   the internal data model is concerned primarily with time stamped
   events containing associations between:

   -   ID of object (or keyword/topic)
   -   URL of resource that holds more detailed information
   -   [ timestamps to help with sorting into chronological order and
       completeness of result sets ]
   -   [ serviceType indicating what kind of resource to expect at the
       URL ]
   -   [ other metadata that provides additional context or is helpful
       for defining access control policies ]

   Furthermore, ESDS may also need to handle an additional data model of
   the access control policies it is expected to enforce by the
   publishers of information.

   Authorization model is outside the scope of IF-MAP (according to the
   footnote 3 on p49 of the IF-MAP protocol), "3 An IF-MAP server
   implementation may provide an authorization model, which protects
   data published by one IF-MAP client from being visible to another IF-
   MAP client.  The specifics of such an authorization model are outside
   the scope of this specification."

   The ability to enforce an authorization model based on policies
   defined by individual publishers is a key functional requirement for

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   ESDS.  Without this, many end-users will not publish data to it if it
   cannot be protected (hidden) from other end-users with whom they do
   not wish to share this information.

   In IF-MAP, the link is an un-named bi-directional binding
   relationship between two identifiers.  (S.2.6.2 of IF-MAP protocol).
   In ESDS, there will be 1-many links: One entity (or information
   provider) may hold information about many different individual
   physical objects (or many different topics / keywords).  One
   individual physical object (or topic/keyword) may be linked [via
   ESDS] to multiple entities that hold more detailed information
   fragments about it.

   However, in supply chain applications, resource owners may prefer
   that the link cannot be discovered the other way, e.g. by querying a
   Discovery Service with the address of a resource in order to retrieve
   a list of IDs of all the objects it claims to hold information about.
   ESDS will need to provide for such directionality restrictions on how
   links can be discovered.

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4.  Related Standards Development Organizations

   Discovery Services is an interesting problem with significant
   challenges for both end-users and service providers.  To tackle these
   challenges, the problem must be approached from both viewpoints, to
   ensure that the final adopted solution meets the needs of all
   organizations involved.

   The EPCglobal Data Discovery Joint Requirements Group (JRG) is in the
   process of gathering use cases and user requirements in order to
   define a Discovery Services standard which can meet the needs of
   supply chain participants and end-users.  In a parallel and
   complementary effort, ESDS is addressing the technical challenges of
   Discovery Services, such as its deployment on public network
   infrastructures.  The final goal is to share the lessons learned in a
   co-operative effort to forge a single standard protocol.

   ESDS is chartered to produce draft proposals for the Discovery
   Service protocol.  Similar to the manner in which the ONS standard
   adopted the approach and architecture developed by the IETF DNS Work
   Group, it is the intention of the ESDS activity that any draft
   protocols developed will be useful to EPCglobal and will help to
   accelerate the development of an EPCglobal standard for Discovery

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5.  Objectives

   This section outlines the objectives of the ESDS protocol.  In an
   effort to convey the goal of each objective, possible solutions are
   provided in order to trigger discussion on the subject matter.

5.1.  Flow Diagrams

   Draft flow diagrams for a directory based model of sharing reference

   Diagram showing the publish of reference information by multiple

 +-------------------------------------------------------------------- +
 |                             ESDS Server                             |
 |                                                                     |
 |                             Community_1                             |
  ^                       ^                       ^
  |ESDS Record Published  |ESDS Record Published  |ESDS Record Published
  |for an individual      |for an individual      |for an individual
  |object X               |object X               |object X
  |(containing reference  |(containing reference  |(containing reference
  | to sources            | to sources            | to sources
  | of information)       | of information)       | of information)
  |Subject to access      |Subject to access      |Subject to access
  |control privileges     |control privileges     |control privileges
  |                       |                       |
 +------------------+    +------------------+    +------------------+
 |  ESDS            |    |  ESDS            |    |  ESDS            |
 |  Publish         |    |  Publish         |    |  Publish         |
 |  Client          |    |  Client          |    |  Client          |
 |                  |    |                  |    |                  |
 |  Organization_1  |    |  Organization_2  |    |  Organization_3  |
 +------------------+    +------------------+    +------------------+

                                 Figure 1

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   Diagram showing the query client sending a request to a virtual
   community to retrieve list of resources for an object or topic.

  |         ESDS                                   |
  |         Client                                 |
  |         Query                                  |
  |                                                +------------------>
  |         Organization_4                         |  3. Reference
  +------------------------------------------------+     information is
    |                       ^                            passed to other
    |1. ESDS Query          |2. ESDS Query response      applications
    |   for an individual   |   for the individual       to access the
    |   object X            |   object X                 detailed
    |                       |   (contains references     information
    |                       |    to sources
    |                       |    of information)
    |                       |   Subject to access
    v                       |   control privileges
 |                     ESDS Server                        |
 |                                                        |
 |                     Community_1                        |

                                 Figure 2

5.2.  Security

   Since ESDS needs to be deployable over a public network
   infrastructure, issues of security and privacy are of heightened
   importance.  Clients must be authenticated to prevent theft of
   information and resources must be authenticated to ensure integrity
   of information.  The information routed over the Internet must be
   encrypted.  It is suggested that the security model should be based
   on open standards, trusted by the industry.

   The ESDS protocol should be decoupled from the security layer and not
   have embedded components specific to certain security protocol
   implementations.  This will enable ESDS implementations to respond
   quickly to changes in the ever advancing security layer protocols.

5.2.1.  Access Control

   An ESDS should provide a resource with the ability to protect its
   link information in order to retain control over which clients are

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   allowed to read this information.  Such rules may be expressed in the
   form of access control policies which are evaluated against the
   client's authentication and authorization credentials and its role in
   relation to the provider of the resource, as well as other criteria
   such as the time elapsed since the link was published.

   ESDS needs to define the granularity of information at which access
   control policies are specified and enforced.  Whether they apply to
   individual events as atomic indivisible entities, or they can specify
   which data fields to include or omit.

   A situation may arise where a client and the provider of a resource
   have no existing trust relationship with each other.  An ESDS should
   allow a resource to specify multiple levels of 'visibility' to such a
   client, so that the resource either remains completely 'silent' or
   'invisible', or so that an opaque handle is visible.  The opaque
   handle should not reveal the identity of the resource in any way, but
   can be used to facilitate the initial negotiation between a client
   and a resource, such as forwarding a number of messages from the
   client to the provider of the resource, provided that the client
   specifies the handle in their message, and provided that an ESDS or
   associated service incorporates such a mechanism.  To protect the
   resource provider and ESDS from additional burden, such a facility
   may be limited in the number of messages which are forwarded and the
   time window following the client's query during which forwarding of
   messages is offered.

   It is recommended that ESDS follows existing standards for defining
   access control policies, such as XACML.  ESDS should study for the
   BRIDGE project work package 4 (Security) on recommendations for
   access control interface and protocols

5.3.  Publish

   An ESDS must provide a mechanism whereby a resource can dynamically
   establish a link for an individual object (or list or range or class
   of objects) that points from the ESDS to the resource.  The link can
   be expressed as a string or URI and it is helpful if this is
   accompanied by an indication of the type of service which can be
   accessed via the link (in order to distinguish between web pages, web
   services, EPC Information Services (EPCIS) and other communication
   mechanisms which might even include phone or fax numbers).

5.4.  Query

   An ESDS should provide a mechanism whereby a client can query the
   ESDS in order to retrieve a list of links to one or more resources.

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   Queries may be one-time queries or standing queries, and an ESDS may
   support either type of query, or both.

   The query interface needs to define the criteria fields as well as
   acceptable criteria values, such as regular expressions or wildcards.

   The ESDS Work Group should decide on whether to support multilayer
   information visibility.  A query with limited access can be informed
   of the existence of information for a particular object, but to view
   the actual information, full access privileges would be required.
   This has particular implications for peer-to-peer searching across
   multiple Discovery Services.  Another scenario to consider is whether
   visibility into the information in the extended fields of a published
   event, should be controlled independently of event information? (i.e.
   should access control policies be sufficiently expressive that they
   can grant or deny access to individual data fields within events,
   rather than simply granting or denying access to events) This has
   particular implications for tracking aggregation and disaggregation
   events and visibility into the entire lifecycle of an object.

5.5.  Relabel/Aggregation/Disaggregation

   To provide complete and resilient visibility across the entire life
   of an object or a product, it is required that changes in identifiers
   are maintained in the Discovery Service layer.

   One scenario for relabeling can be a Discovery Service for
   maintenance of installed software packages.  An organization with a
   multitude of machines, deployed anywhere on the Internet could use DS
   to notify machines about the availability and location of (secure and
   tested) updates to packages.  Each machine can submit standing-
   queries to the DS, for all the packages that are installed on it
   locally.  The organization operators would test and verify every new
   release of a package.  Once a package is approved, it is placed on
   trusted file servers and the link to those files (and any mirror
   links) is published to DS along with the package name.  This would
   result in all the machines with standing-queries to be notified of
   the new downloadable and verified package.  Package name change is a
   common phenomena, specially when the version number is appended to
   the package name (e.g. wxWidgets libraries).  So ESDS needs to
   provide relabeling facilities in order to be comprehensive enough to
   address a wide range of problem domains.

   Another scenario requiring the capture of aggregation and
   decomposition events is the regulation of the European parliament
   with respect to the cold supply chain regarding the tracking of fresh
   meat.  For example, as a cow moves from a farm into the supply chain
   where it is finally sold as beef to a consumer at a retail store, it

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   is vital that relabelling and disaggregation events can be stored
   within a Discovery Service in order to enable querying information
   about the entire lifecycle of the cow "from farm to fork" While
   having access control over visibility of these kind of events is
   desired, it is recommended that Discovery Services should not attempt
   to interpret or validate these events.  It has been suggested that
   these complexities be excluded from the core of ESDS, instead
   facilitating them via the extensions mechanism and/or leaving such
   interpretation, validation and analysis to client applications that
   query ESDS.  This approach must also give consideration to providing
   access control to the extension information.

5.6.  Multiple Organizations

   It is the intention of ESDS to provide authorized clients with the
   link referral information necessary to enable client applications to
   gather information from multiple organizations covering an object's
   or a topic's lifespan.  For a product this could include link data
   from the design phase, through manufacture, distribution and retail,
   usage period (including service, repair, maintenance, overhaul) and
   even end-of-life phase (including collection, sorting,
   remanufacturing and recycling).  So it could be desirable to record
   the current phase.  Also there may exist lifecycle steps within a
   particular phase, a higher perspective or meta view could show that
   entire phase as a single step in the life of the product.  For
   example, a product can be in a Manufacturing supply chain, then move
   into a Logistics supply chain, followed by a Service supply chain.
   Each of these particular supply chains may have their own set of
   lifecycle steps, but the entire lifecycle is spread across all three
   supply chains.  ESDS should facilitate the linking of these supply
   chains and phases together to enable the capture of the entire
   lifecycle of the object.

5.7.  Identifier Agnostic

   To enable the grouping of information belonging to the same object,
   each object needs to be uniquely identifiable.  Information about the
   object is held by a number of independent organizations that agree to
   use a shared identifier schema.  These identifier schemas are defined
   and distributed by numbering authorities in each industry sector.
   Some numbering authorizes guarantee global uniqueness of the issued
   identifiers, but this is not the case all the time.  Especially when
   there exists issued legacy numbers currently in use within the domain
   of a numbering authority.  Also there are cases were numbering
   authorities for different domains have collisions in their space of
   issued identifiers (e.g.  Animal Identification Number (AIN),
   National Stock Numbers (NSN), and the International Mobile Equipment
   Identity (IMEI) are all 15 digit identities and there are collisions

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   in the space of issued identities.).

   There are procedures for converting identifiers to URIs which can
   also assure that the URI is globally unique.  However although global
   uniqueness of identifiers is highly desirable for use within a co-
   operating federation of Discovery Services, it is not a requirement
   for each individual instance of a Discovery Service, and it would be
   out of scope for a Discovery Service to verify global uniqueness for
   identifiers used.

   To define a protocol which is applicable to all scenarios, it is
   essential that the protocol supports various numbering authorities.
   The ESDS protocol should have a broad scope and support multiple
   identifier schemes including schemas with non-unique identifiers.
   The intelligent handling of identifier associated with an object is
   out of scope of Discovery Services and can be handled accordingly by
   ESDS query applications.  It must also be identifier agnostic in
   order for Discovery Services to be embraced by all potential

5.7.1.  Reusing Identifiers

   There are scenarios where the same object (and its identifier) is
   used within a Discovery Service but in different sessions or phases.
   It could be the case that the authorization and access control
   policies differ based on attributes such as timestamps, or metadata.
   An identifier reuse scenario can be for reusable assets and other
   returnable transport items that may circulate among multiple
   organizations - and in many situations, it may be more economical and
   more feasible to tag the reusable asset than to tag its contents.
   This is particularly true when attaching not only a unique ID tag but
   also environmental sensors to the reusable asset.

   Company A that provides and manages reusable assets can provide an
   additional service to its customers, such as company B (which borrows
   or leases an asset from company A), by allowing company B to access
   data about the asset while it carries the products from company B. At
   the same time, there are benefits to company A in being able to track
   its own assets, to balance supply and demand of assets and detect
   when assets are not being returned correctly, e.g. for cleaning and

   However, it is also very important to protect the confidentiality of
   the data for company B from its competitor, company C, who may happen
   to use the same asset at a later time.

   One possible solution to this is for company A to dynamically manage
   access permissions to data about the asset and its contents using

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   time-based windows that provide its customers with visibility only to
   data about the asset during the time periods when it is associated
   with their products or their lease/use of the asset.

   This could be achieved by appending additional time-based constraint
   qualifications to access control policies.

   For example, company B could be granted visibility to track and trace
   data about the asset for events that occur after they take custody of
   the asset and before they relinquish custody of the asset.  Company C
   might be granted access for a different time window.  There should be
   no overlap between the time windows granted to competing companies,
   in order to protect the confidentiality of their data.

5.8.  Extensible

   The event data needs to accommodate various scenarios and their
   business requirements.  Therefore it must be an extensible protocol
   which enables the collaborating organizations to communicate messages
   specific to their industry and terminology.

   An ESDS protocol should enable the sharing of information without
   involving the business rules of various scenarios.  This will keep
   the interface clean and uniform across all scenarios and ESDS

   ESDS should give consideration to approaches for dealing with access
   control and visibility of extended information and protocols.  One
   approach could be to provide one level of access to all the event
   information, whereby if a client can access an event information, it
   can retrieve the extended information.  Another approach could be to
   provide multilayer visibility, where only clients with proper
   privileges can retrieve the extended information.

5.9.  Policies

   The Retention policy for data records in ESDS would vary based on the
   business and regulatory requirements.  Some scenarios would need
   retention of only few days and some would require retention for 30
   years.  Some other policies with similar parameters but different
   interpretation are the archiving policies, purging policies, and
   audit policies.

5.10.  Stale Links

   There are situations where the link information (such as a URL) that
   was originally specified is no longer effective (e.g. because the
   provider of the resource has not taken care to maintain redirection

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   from the original link address to the new location of the resource
   when restructuring a website or moving to a different domain name).
   In such situations, it is desirable that a Discovery Service could
   provide a client with link information that is current and effective.
   For audit purposes, it may also be necessary for an ESDS to be able
   to retain and reconstruct the original (or previous) link
   information, even if it is no longer effective.

   This may also imply that an ESDS should allow a resource provider to
   loosely couple the link record with the current link address, to ease
   migration of multiple records to a new resource address, while still
   providing a mechanism to recover a full audit trail of such changes
   of link addresses.  This is particularly important when the link
   records are digitally signed and we wish to avoid having to "void"
   such records merely because they embedded a URL which is no longer in

5.11.  Peer-to-Peer Communications

   Architecting a bootstrapping policy will involve defining a protocol
   for peer-to-peer communication between Discovery Services (DS).  The
   ultimate goal is to locate the target DS without dependence on
   hierarchical information and services such as ONS or the underlying
   DNS.  To facilitate the peer-to-peer communication it is recommended
   that existing protocols and proven architectures such as JXTA
   [jxta-protocols] be utilized.  Another candidate architecture is
   ECRIT's approach to locating authoritative sources of information in
   a peer-topeer network [ecrit-mapping-arc].

   One point to keep in mind with DSs is that finding one target DS does
   not mean that the search is over.  One object identifier could be
   acceptable to many DSs; therefore a search cannot stop once a DS is
   located but needs to propagate to all peers.

   Care and consideration must be given to privacy and the sensitivity
   of information at the DS nodes.  It is also critical that steps are
   taken to protect against increased vulnerabilities that the extra
   exposure that P2P brings, such as denial-of-service attacks, or data
   mining tricks.

   Another challenge is when the target DS is successfully located.  How
   much information on an object inquiry can that DS share with the peer
   DS, without jeopardizing security and privacy?  Should the DSs
   facilitate the peer-to-peer access negotiation process or should it
   be done by the Certificate Authority?

   A sample scenario would be a query client negotiating for access to
   information from an organization where the information-providing

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   organization does not have an established business (trust)
   relationship with the client and therefore chooses initially not to
   reveal its identity to the client.  In this case, it is possbile to
   use the opaque 'node ref' concept and perhaps each object can have
   such a 'node ref' handle to deal with such scenarios
   [bridge-discovery-services-design].  Considerations must be given to
   protection against data mining to discovery whether a serial number
   exists or has been issued.

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6.  Technical Challenges

   ESDS should be purely an application layer protocol disassociated
   from implementation specifics and challenges.  Below are some of the
   technical challenges that certain business requirements demand.
   However ESDS is not chartered to address these implementation

6.1.  Auditability

   Based on some business and regulatory requirements, auditing
   capabilities should be facilitated by ESDS to provide accountability
   if and when something goes wrong.  With an auditing mechanism, record
   data can be tracked and the person responsible identified, thus a
   series of data records can be reconstructed at a later date, allowing
   the Discovery Service operators to prove who was responsible for
   which data records [bridge-security-analysis].

6.2.  Responsiveness

   ESDS implementations will need to be designed to accept updates in a
   close to real time basis from multiple providers of information
   across the globe.  Because they store serial-level records, they will
   need to be sufficiently scalable to store large volumes of data,
   possibly up to trillions of records per year.

6.3.  Availability

   ESDS availability requirements would vary from business case to
   business case.  Research by BRIDGE shows that the uptime requirements
   for some supply chain business cases are 99.99% year round.

   It is expected that the ESDS instances will be available over a
   shared network that exposes them to the effects of network attacks.
   Furthermore, in many cases it is expected that these components
   should be globally reachable from the Internet and not hosted on a
   secure private network.  Such components are also built using
   commonly available Operating Systems and middleware (e.g.
   Application Servers).  Thus they are also subject to any
   vulnerabilities of these supporting systems.

   A major security issue for shared services such as the ESDS is
   service availability.  In particular if services are considered to be
   vital for businesses and organizations (e.g. "pharma e-Pedigree" or
   "product-authentication") ESDS needs to be able to guarantee minimal
   amount of service downtime due to security vulnerabilities and
   attacks [bridge-security-analysis].

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7.  Related Activities

   Currently, the standards organization EPCglobal, and EU research
   projects BRIDGE, SMART, and PROMISE are looking into the global
   supply chain track-and-trace challenge.  As part of their research,
   each of them has identified the need for Discovery Services to link
   resources and clients in the supply chains.

   EPCglobal is beginning to gather user requirements for Discovery
   Services.  However, EPCglobal is a paid membership organization
   focused on serving their own subscriber community.  Although the
   final ratified EPCglobal standards are open and freely available to
   download, the subscription fees for joining the EPCglobal community
   may deter a significant proportion of the end-user community from
   directly participating in the development of their global standards.

   IETF would be the ideal body to oversee the development of this
   protocol because of its deep knowledge of Internet infrastructure and
   experience with development of application layer protocols.

   An IETF working group would be an inviting and open community which
   facilitates contribution and participation of all interested parties
   involved in the global supply chain as well as other potential
   industries with organizations enthusiastic about the benefits of
   collaboration with each other.  The output would be released as a
   freely available RFC in the public domain.  ESDS will make best
   efforts to ensure good communication with complementary activities at
   EPCglobal, in order to ensure that the output of ESDS is as relevant
   and useful as possible to a future EPCglobal standard for Discovery

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8.  Acknowledgements

   This document and the process of authoring was made possible by the
   excellent xml2rfc tool [RFC2629].  Credit must also be given to Scott
   Hollenbeck author of [RFC4930] for the organization and grouping of
   RFC sections.

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9.  Contributors

      Dr. Mark Harrison
      Senior Research Associate, Distributed Information and Automation
      Director, Auto-ID Labs at Cambridge
      Institute for Manufacturing
      University of Cambridge
      Mill Lane
      Cambridge, UK
      CB2 1RX

      Phone: +44-(0)1223-338178
      Email: mark.harrison@cantab.net

      Michael Young
      Senior Director, Technology
      Afilias Canada
      204-4141 Yonge Street
      Toronto, ON M2P 2A8

      Phone: +1-416-646-3304
      Email: myoung@ca.afilias.info

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10.  IANA Considerations

   This document has no actions for IANA.

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11.  Security Considerations

   This document is a problem statement that does not by itself
   introduce any security issues.

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12.  References

12.1.  Normative References

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC4930]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              RFC 4930, May 2007.

12.2.  Informative References

              BRIDGE, "BRIDGE WP02 High-level design for Discovery
              Services", August 2007.

              BRIDGE, "BRIDGE WP04 Security Analysis Report: RFID
              Network Confidentiality (D 4.5.1)", December 2007.

              BRIDGE, "BRIDGE WP04 Security Analysis Report", July 2007.

              BRIDGE, "BRIDGE WP02 Serial Level Lookup Requirements",
              August 2007.

              Thompson, F., "Extensible Supply-chain Discovery Service
              Commands (work in progress)", February 2008.

              Thompson, F., "Extensible Supply-chain Discovery Service
              Schema (work in progress)", February 2008.

              Schulzrinne, H., "Location-to-URL Mapping Architecture and
              Framework", September 2007.

              EPCglobal Information Services Work Group, "EPCglobal
              Information Services", September 2007.

              EPCglobal, "Object Naming Service 1.0", October 2005.

              EPCglobal Tag Data Standard Work Group, "EPC Tag Data

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              Standard Standard", March 2006.

              Duigou, M., "JXTA v2.0 Protocols Specification",
              June 2004.

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