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) ). Unfortunately, the vCard format has several major drawbacks:
It is becoming increasingly important to define a robust, extensible format for describing entities on the Jabber network. Such a format should be:
Information about entities is provided using the Infobits (XEP-0120)  protocol and registered infobit keynames (mainly those specified in vCard Infobits Mapping (XEP-0125)  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) ). The metadata is discovered by interacting with a common Service Discovery (XEP-0030)  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.
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.
The entity returns its associated items:
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.
The entity returns its metadata to the requestor.
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) . 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.
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).
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
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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.
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Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
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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".
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/>.
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Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/