XEP-0123: Entity Metadata

NOTE: This proposal was retracted by the author on 2004-02-19.
Peter Saint-Andre
© 2003 – 2003 XMPP Standards Foundation. SEE LEGAL NOTICES.


WARNING: This document has been retracted by the author(s). Implementation of the protocol described herein is not recommended. Developers desiring similar functionality are advised to implement the protocol that supersedes this one (if any).
Standards Track
0.3 (2003-12-16)
Document Lifecycle
  1. Experimental
  2. Retracted
  3. Proposed
  4. Stable
  5. Final

1. Background and Requirements

Traditionally, the only mechanism for communicating detailed information about entities on the Jabber network has been an XML version of the vCard format for electronic business cards (see vcard-temp (XEP-0054) [1]). Unfortunately, the vCard format has several major drawbacks:

  1. It is mainly limited to data about persons (although it has been used on the Jabber network to describe things like servers).
  2. The format contains relatively few data fields.
  3. The format is not extensible.
  4. As implemented, the data is not searchable.
  5. As implemented, the data cannot be filtered depending on the identity of the requestor.

It is becoming increasingly important to define a robust, extensible format for describing entities on the Jabber network. Such a format should be:

  1. Applicable not just to people but to any entity on the network, including but not limited to servers, components, bots, Multi-User Chat (XEP-0045) [2] rooms, Publish-Subscribe (XEP-0060) [3] nodes, and in general anything that can be addressed as a Jabber ID (as defined in XMPP Core [4]).
  2. Usable in encapsulating any information about the entity itself (name, address, description, title, etc.).
  3. Extensible enough to handle any metadata that may be needed for current and future applications (including, at a minimum, everything that can be defined in vCard); it must be possible to use it for public protocols defined by the IETF or XMPP Standards Foundation as well as for custom or private protocols.
  4. Well-defined enough, through datatyping and public registries where applicable, to enable robust searching and filtering based on defined data fields and their values.

2. Protocol

Information about entities is provided using the Infobits (XEP-0120) [5] protocol and registered infobit keynames (mainly those specified in vCard Infobits Mapping (XEP-0125) [6] although entity metadata is by no means limited to vCard information and could include infobits such as those specified in Dublin Core Infobits Mapping (XEP-0121) [7]). The metadata is discovered by interacting with a common Service Discovery (XEP-0030) [8] node named "metadata". The queried entity replies with a service discovery result containing any infobits that the entity wishes to reveal about itself to the requesting entity. This information is always metadata about the entity itself, not any other entities or any relationships that the entity may have to other entities.

3. Use Cases

3.1 Discovering Support

Support for entity metadata is discovered by means of Service Discovery. If the queried entity provides metadata about itself, it SHOULD advertise that fact by listing an item named "metadata" in response to a disco#items query.

Example 1. One Entity Queries Another via Disco
<iq type='get'
  <query xmlns='http://jabber.org/protocol/disco#items'/>

The entity returns its associated items:

Example 2. Entity Returns Disco Item Results
<iq type='result'
  <query xmlns='http://jabber.org/protocol/disco#items'>
    <item jid='juliet@capulet.com'
          name='Information about Juliet Capulet'/>

3.2 Requesting Metadata About Another Entity

In order to request the advertised metadata, the requesting entity sends a disco#info request to the 'metadata' node of the JID communicated in the previous result.

Example 3. Requestor Requests Metadata
<iq type='get'
  <query xmlns='http://jabber.org/protocol/disco#info'

The entity returns its metadata to the requestor.

Example 4. Entity Returns Metadata Result
<iq type='result'
  <query xmlns='http://jabber.org/protocol/disco#info'
    <info 'http://jabber.org/protocol/infobits'>
      <bit key='fn'>Romeo Montague</bit>
      <bit key='country'>Italy</bit>
      <bit key='city'>Verona</bit>
      <bit key='gender'>male</bit>
      <bit key='nickname'>loverboy</bit>

4. Integration with Directory Services

One of the primary motivations behind this proposal is to enable the construction of useful directory services on the Jabber network. Examples of such services include but are not limited to:

Although such directories will be a valuable addition to the network, it is imperative to understand that the canonical source for metadata about an entity is the entity itself. Mechanisms for keeping directories synchronized with entities are outside the scope of this document, and in any case a directory may not be privy to all information about an entity (since in general a user should publish to a directory only the information that he or she deems world-readable).

Directories SHOULD require registration using In-Band Registration (XEP-0077) [9]. Before registering with a directory, an entity SHOULD adjust its access controls or privacy rules accordingly, including appropriate definition of classes and addition of the directory server's JID to the relevant privacy rules. Upon accepting registration from an entity, a directory SHOULD immediately send a metadata request to the registering entity. Synchronization of metadata is a matter for the directory implementation to determine, and perhaps negotiate with the registering entity; all such synchronization and negotiation is out of scope for this document.

5. Security Considerations

Metadata MAY be world-readable. Entities MUST take care to ensure that they exercise proper control over access to such information. Users of IM clients SHOULD be warned that their data may be world-readable and be given the option to not publish such information or control it via appropriate mechanisms (such as privacy rules).

6. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [10].

7. XMPP Registrar Considerations

7.1 Service Discovery Nodes

Upon advancement of this proposal to a status of Draft, the XMPP Registrar [11] shall add the 'metadata' node to its registry of common Service Discovery nodes.


Appendix A: Document Information

XMPP Standards Foundation
Standards Track
Last Updated
Approving Body
XMPP Council
XMPP Core, XMPP IM, XEP-0030, XEP-0120
Superseded By
Short Name
Source Control

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Appendix B: Author Information

Peter Saint-Andre


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Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <https://xmpp.org/community/> for a complete list.

Errata can be sent to <editor@xmpp.org>.

Appendix F: Requirements Conformance

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

Appendix G: Notes

1. XEP-0054: vcard-temp <https://xmpp.org/extensions/xep-0054.html>.

2. XEP-0045: Multi-User Chat <https://xmpp.org/extensions/xep-0045.html>.

3. XEP-0060: Publish-Subscribe <https://xmpp.org/extensions/xep-0060.html>.

4. RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc6120>.

5. XEP-0120: Infobits <https://xmpp.org/extensions/xep-0120.html>.

6. XEP-0125: vCard Infobits Mapping <https://xmpp.org/extensions/xep-0125.html>.

7. XEP-0121: Dublin Core Infobits Mapping <https://xmpp.org/extensions/xep-0121.html>.

8. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.

9. XEP-0077: In-Band Registration <https://xmpp.org/extensions/xep-0077.html>.

10. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

11. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.

Appendix H: Revision History

Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/

  1. Version 0.3 (2003-12-16)
    Incorporated infobits changes and vCard infobit mappings; metadata about relationships to be moved to forthcoming specification.
  2. Version 0.2 (2003-10-23)
    Changed ent to entity, rel to relation.
  3. Version 0.1 (2003-10-22)
    Initial version, split off from XEP-0120.

Appendix I: Bib(La)TeX Entry

  title = {Entity Metadata},
  author = {Saint-Andre, Peter},
  type = {XEP},
  number = {0123},
  version = {0.3},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-0123.html},
  date = {2003-10-22/2003-12-16},