Many Jabber protocols need to define metadata about "things" on the Jabber network; such things are not limited to entities that are addressable as JIDs (e.g., users, servers, services, and chatrooms) nor even to things that are addressable as Publish-Subscribe (XEP-0060)  or Service Discovery (XEP-0030)  nodes (e.g., Ad-Hoc Commands (XEP-0050) ), but may include anything that Jabber entities can communicate about, including files sent via Jabber file transfer protocols (e.g., Out-of-Band Data (XEP-0066)  and SI File Transfer (XEP-0096) ), information published via pubsub protocols (e.g., User Tune (XEP-0118) ), and other Jabber phenomena. To date, Jabber protocols have used disparate, specialized formats for capturing such meta-information. This document provides a generic information format that can be included whenever a protocol needs to define metadata about something on the network.
The format defined herein uses a simple "key-value" structure. Although this may seem contrary to the XML basis of Jabber technologies, there are at least two good reasons for pursuing this approach:
Using namespaced XML elements would force implementations to maintain a record of all namespaces and to differentiate those that define actionable protocols (e.g., 'http://jabber.org/protocol/si') from those that define informational metadata formats (e.g., 'http://purl.org/dc/elements/1.1'); the only way to do this would be to maintain an internal list of all possible namespaces that might be encountered by an application on the network.
Not all metadata formats that the Jabber community may want to use exist in stable XML representations (e.g., this is true of the vCard format) or in representations for which namespaces exist. In addition, some metadata formats (e.g., Friend of a Friend (FOAF) ) exist only in Resource Description Framework , whose syntax is represented in XML but whose semantics impose a more complex structure that requires a specialized (non-XML) parser. As long as a clear mapping can be defined between such metadata formats and Jabber infobits, consistent information representation and exchange can be preserved.
The "infobits" protocol defined herein provides a data format only. The container element is <info/>, which is qualified by the 'http://jabber.org/protocol/infobits' namespace. There is one allowable child of the <info/> element -- <bundle/> -- and one allowable child of the <bundle/> element -- <bit/>. In order to provide the relevant metadata, the <info/> element MAY contain an unbounded number of <bundle/> elements, each of which MAY contain an unbounded number of <bit/> elements.
Each <bundle/> element MUST possess a 'type' attribute, whose value specifies the aspect of reality to which the enclosed bits apply (e.g., geographical location). A <bundle/> element MAY also possess a 'context' attribute, whose value provides further specifying information about the kind of entities described by this bundle (e.g., a home address as opposed to a work address).
Each <bit/> element MUST possess a 'key' attribute, whose value specifies the name of the key (this MUST be an NMTOKEN as defined in XML 1.0 ). A <bit/> element MAY also possess a 'datatype' attribute, whose value specifies the datatype of the key (which SHOULD be a datatype specified in XML Schema Part 2  or in a registry of values maintained by the XMPP Registrar, such as those described in Data Forms Validation (XEP-0122) ). The <bit/> element SHOULD contain XML character data that specifies the relevant value of the 'key'. A <bundle/> element MAY contain more than one <bit/> element with the same value for the 'key' attribute when necessary (e.g., two instances of 'weblog' if the person has multiple weblogs), but obviously SHOULD NOT do so if a collision would occur (e.g., two instances of 'lat' and 'lon' to define a geographical location).
Note well: no keys are defined in this document. All such keys MUST be defined in separate specifications. Keys and associated values shown in this document are provided for explanatory purposes only.
Data provided via the infobits protocol MAY be world-readable. Access control considerations MUST be defined by any protocol that makes use of infobits.
Info key names registered with the XMPP Registrar MUST be considered as identifiers, not English-language words. For purposes of internationalization, an identifier SHOULD be rendered as a word or phrase that is appropriate to the end user's preferred language.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
The XMPP Registrar shall maintain a registry of infobit keynames and associated information.
All keynames MUST begin with a short prefix string (letters and numbers only), followed by the '.' character used as a separator, followed by the name of the key as determined by the particular specification or organization that is identified with the prefix. Arbitrary keynames SHOULD begin with a prefix consisting of the capital 'X' character.
The XMPP Registrar shall at its discretion reserve certain keyname prefixes for use in specifying particular classes of information. One example is the prefix 'DC', which is reserved for use by infobits specified by the Dublin Core Metadata Initiative (DCMI)  (for details, see Dublin Core Infobits Mapping (XEP-0121) ). Furthermore, the XMPP Registrar shall reserve the "XMPP" prefix for infobits related to documents created by the XMPP Working Group  or its successors, and shall reserve the upper-case versions of all protocol "shortnames" specified in XMPP Extension Protocol specifications (e.g., a prefix of "MUC" for infobits related to Multi-User Chat (XEP-0045) ).
In order to prevent naming collisions, infobits that will be used in public protocols that may interoperate with other protocols on the network SHOULD be registered with the XMPP Registrar, and MUST be so registered if they are defined in XMPP Extension Protocol specifications (however, registration of private keys is NOT REQUIRED). Registration with the XMPP Registrar shall be considered to entail reservation of that infobit on the network, and a registered bit MUST NOT be re-used by other protocols and applications for purposes other than those implied by the registry entry.
In addition to the key name, the following data may be provided (but is not required) for each bit:
The registry format is as follows:
Before defining a new protocol for metadata, the primary author of this proposal investigated several promising technologies that could be used to meet the above requirements -- in particular, the Friend of a Friend (FOAF) vocabulary, which is a subset of the Resource Description Framework (RDF). Ultimately, the primary author concluded that, while FOAF and RDF have many merits, they are not ideal for use on the Jabber network. In particular:
Given these and other concerns, the primary author concluded that the best course would be to define an extensible XML protocol that can be processed using tools that are standard within existing Jabber/XMPP implementations, that allows only the entity itself to define metadata about itself, and that is under the control of the Jabber/XMPP community.
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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.
The primary venue for discussion of XMPP Extension Protocols is the <email@example.com> discussion list.
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".
13. 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/>.
14. 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/>.
15. The Dublin Core Metadata Initiative (DCMI) is an organization dedicated to promoting the widespread adoption of interoperable metadata standards. For further information, see <http://www.dublincore.org/>.
17. The XMPP Working Group was created by the Internet Engineering Task Force to define an adaptation of the base Jabber protocols that could be considered an IETF-approved instant messaging and presence technology. For further information, see <https://datatracker.ietf.org/wg/xmpp/charter/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/