XEP-0209: Metacontacts

This document specifies an XMPP protocol extension for defining metacontacts and grouping member JIDs.

NOTICE: This document is currently within Last Call or under consideration by the XMPP Council for advancement to the next stage in the XSF standards process.

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Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) 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.

Conformance Terms

The following 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".

1. Introduction
2. Requirements
3. Overview
4. Use Cases
    4.1. Retrieving the metacontact data
    4.2. Storing the metacontact data
5. Implementation Notes
    5.1. Creating a metacontact
    5.2. Removing a metacontact
    5.3. Uniqueness of order within a metacontact
6. Security Considerations
7. IANA Considerations
8. XMPP Registrar Considerations
9. XML Schema
Notes
Revision History

1. Introduction

It is often the case that a user will have multiple representations of a single contact, either within one account (as is often the case with contacts using legacy systems through transports) or across several accounts (particularly where a user or contact has separate work and home accounts). As these are different representations of the same logical entity, this XEP provides a method for binding them together into a single meta-contact.

2. Requirements

The authors have designed the metacontacts protocol with the following requirements in mind:

3. Overview

<meta jid='romeo@montague.net' tag='d93nov' order='0'>

4. Use Cases

Below are example of setting and retrieving metacontacts for an account. When using metacontacts across multiple accounts, the steps are identical and the 'tag' attributes and used across accounts (that is: when the same tag is used for multiple contacts, all entries with the tag are merged into a single metacontact whether they reside on the same of different accounts).

4.1 Retrieving the metacontact data

Upon login, a client will need to know the current state of the metacontact structure and so SHOULD request the state for each account.

Example 2. Requesting metacontacts

<iq type='get' id='get1'>
  <query xmlns='jabber:iq:private'>
    <storage xmlns='storage:metacontacts'/>
  </query>
</iq>

The result of the query will list the metacontact membership for roster entries belonging to the queried account.

Example 3. Server returns metacontact data

<iq type='result' id='get1'>
  <query xmlns='jabber:iq:private'>
    <storage xmlns='storage:metacontacts'>
      <meta jid='mike.bolton@raplovers.org' tag='ae18f2' order='1'/>
      <meta jid='tom@jump-to-conclusions.com' tag='82a1a5' order='1'/>
      <meta jid='samir@initech.com' tag='283b94' order='2'/>
      <meta jid='mike@initech.com' tag='ae18f2' order='2'/>
    </storage>
  </query>
</iq>

The meta tags each represent a contact which is a member of a metacontact; as such it is likely that some roster entries for an account will not have corresponding meta tags (if they are not members of a metacontact). Each 'meta' tag MUST have a 'jid' attribute and a 'tag' attribute, an optional 'order' attribute MAY be included.

The value of the 'jid' attribute MUST be the bare JID of a contact which is a member of the described metacontact and any jid MUST NOT be specified in this manner as a member of more than one metacontact within an account. A JID specified as a member of a metacontact for an account SHOULD be a member of the roster for that account.

The value of the 'tag' is used as a non-human readable unique identifier for a metacontact. In the above example, there are three metacontacts; those with tags of '82a1a5' and '283b94' each have only one contact on this account, while the metacontact with tag tag='ae18f2' contains two contacts.

The value of the 'order' attribute is used to suggest preference of some contacts over others within a metacontact; those contacts with a higher order are preferable to those with a lower order. In this example, 'mike@initech.com' is considered preferable to 'mike.bolton@raplovers.org' when communicating with the metacontact with tag 'ae18f2', due to their order of 2 and 1 respectively.

Note: It is entirely possible for the query result for an account to indicate that, in isolation from other accounts, there exist metacontacts which contain only a single member contact, as is the case in the above example. The client MUST NOT discard such data, as other accounts belonging to the user (which the client need not have details of) may also have members of this metacontact.

4.2 Storing the metacontact data

Example 4.

<iq type='set' id='set2'>
  <query xmlns='jabber:iq:private'>
    <storage xmlns='storage:metacontacts'>
      <meta jid='mike.bolton@raplovers.org' tag='ae18f2' order='1'/>
      <meta jid='tom@jump-to-conclusions.com' tag='82a1a5' order='1'/>
      <meta jid='samir@initech.com' tag='283b94' order='2'/>
      <meta jid='milton@hawaii.com' tag='492ab2' order='2'/>
      <meta jid='joanna@kung-fu.org' tag='9248cc' order='1'/>
    </storage>
  </query>
</iq>

Example 5. Server returns

<iq type='result' id='set2'/>

5. Implementation Notes

5.1 Creating a metacontact

Creation of a metacontact is uncomplicated; the simple addition of meta tag with a common tag results in a new metacontact.

5.2 Removing a metacontact

Similarly, to remove a metacontact all that is required is to remove the meta tags which contribute to the metacontact.

5.3 Uniqueness of order within a metacontact

Although it is unavoidable that multiple contacts within a metacontact MAY have the same order (due to potentially unavailable information from other accounts), clients SHOULD NOT apply the same order to multiple members of the same metacontact where it is possible to avoid it. If multiple members of a metacontact have the same order, the behaviour is dependent upon the client; it MAY apply rules itself to determine which member to communicate with (based upon presence, recent activity or other methods) it MAY present the user with the option to sort the members such that the orders are again unique, or it MAY employ another appropriate action.

As the order attribute is optional, clients need a method for determining which member contact to use where the metacontact consists entirely of unordered members. When ordered and unordered members are present, unordered members SHOULD be considered to have the lowest order.

6. Security Considerations

Security considerations related to private XML storage are described in XEP-0049; this XEP introduces no additional concerns.

7. IANA Considerations

8. XMPP Registrar Considerations

No namespaces or parameters need to be registered with the XMPP Registrar [2] as a result of this XEP.

9. XML Schema

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='storage:metacontacts'
    xmlns='storage:metacontacts'
    elementFormDefault='qualified'>

  <xs:element name='metacontacts'>
    <xs:complexType>
      <xs:sequence>
        <xs:element ref='meta' minOccurs='0' maxOccurs='unbounded'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name='meta'>
    <xs:complexType>
      <xs:attribute name='jid' type='xs:string' use='required'/>
      <xs:attribute name='tag' type='xs:string' use='required'/>
      <xs:attribute name='order' type='xs:xs:unsignedInt' use='optional'/>
    </xs:complexType>
  </xs:element>
</xs:schema>