XEP-0453: DOAP usage in XMPP

This specification defines how XMPP projects can provide a machine-readable description of their abilities, and how external entities can interact with it.
Emmanuel Gil Peyrot
© 1999 – 2020 XMPP Standards Foundation. SEE LEGAL NOTICES.


WARNING: This Informational document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the best practice or protocol profile described herein is encouraged in exploratory implementations, although production systems are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.
0.1.0 (2021-01-26)
Document Lifecycle
  1. Experimental
  2. Proposed
  3. Active

1. Introduction

Gathering information on many implementations has always been a chore, there exist various lists or comparisons for XMPP clients, servers and libraries, but these are often out of date, inaccurate, incomplete, or generally unmaintained.

This specification aims at solving this problem by putting the work of publishing and keeping up to date said information onto the maintainers of the software. Given many already do maintain this kind of list, the inconvenience should be minimal.

The information listed SHOULD include, but isn’t limited to, the project name, homepage, description, logo, screenshots if relevant, specifications supported (RFCs and XEPs). A full list of supported properties is described in RDF format at http://usefulinc.com/ns/doap#.

A central point should be defined to gather the list of implementations publishing their information, this specifications proposes xmpp.org for this purpose.

2. Requirements

Creating, publishing and maintaining a project description should be as easy as possible for producers.

Fetching, parsing and using a project description should be as easy as possible for consumers.

These two requirements have oriented the choice of technologies towards being as restrictive as possible:

3. Glossary

Description of a Project, the chosen RDF format used by this specification to describe the various properties of a project.
Resource Description Framework, a generic data model framework, supporting many serialisation formats and conversions between them. For the purpose of this specification we will only consider RDF/XML, an XML serialisation format, with the rationale that all XMPP authors are already familiar with this serialisation format.

4. Use Cases

A user might want to know which compliance suite level a given client supports before choosing it.

A sysadmin might want to know which compliance suite level a given server supports before choosing it.

An XMPP service might want to propose clients based on their advertised support of what they consider a modern client.

A specification author might want to know the list of projects implementing this specification, their support level and version.

An XMPP enthousiast website might want to automatically update their XMPP comparison page with up to date information.

4.1 Examples

This specification won’t list every property one could add to their DOAP file, that is the role of the DOAP specification, so it will start with examples.

Here is a minimal DOAP file, containing the same data as the XMPP Software Listing:

Example 1. A Minimal DOAP File
<?xml version='1.0' encoding='UTF-8'?>
<rdf:RDF xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'
  <Project xml:lang='en'>
    <homepage rdf:resource='https://poez.io'/>

But a lot more information can be added:

Example 2. A More Featureful DOAP File
<?xml version='1.0' encoding='UTF-8'?>
<rdf:RDF xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'


    <shortdesc xml:lang='en'>Free console XMPP client</shortdesc>
    <shortdesc xml:lang='fr'>Client XMPP libre en console</shortdesc>

    <description xml:lang='en'>Free and modern console XMPP client written in Python with the ncurses library</description>
    <description xml:lang='fr'>Client console XMPP libre et moderne, écrit en Python avec la bibliothèque ncurses</description>

    <homepage rdf:resource='https://poez.io/'/>
    <schema:documentation rdf:resource='https://doc.poez.io/'/>
    <download-page rdf:resource='https://poez.io/#download'/>
    <bug-database rdf:resource='https://lab.louiz.org/poezio/poezio/-/issues'/>
    <developer-forum rdf:resource='xmpp:poezio@muc.poez.io?join'/>
    <support-forum rdf:resource='xmpp:poezio@muc.poez.io?join'/>

    <license rdf:resource='https://git.poez.io/poezio/plain/COPYING'/>


    <schema:logo rdf:resource='https://poez.io/img/logo.svg'/>
    <schema:screenshot rdf:resource='https://poez.io/img/screenshot.png'/>



    <category rdf:resource='https://linkmauve.fr/ns/xmpp-doap#category-client'/>

        <browse rdf:resource='https://lab.louiz.org/poezio/poezio'/>
        <location rdf:resource='https://lab.louiz.org/poezio/poezio.git'/>

    <implements rdf:resource='https://xmpp.org/rfcs/rfc6120.html'/>
    <implements rdf:resource='https://xmpp.org/rfcs/rfc6121.html'/>
    <implements rdf:resource='https://xmpp.org/rfcs/rfc6122.html'/>
    <implements rdf:resource='https://xmpp.org/rfcs/rfc7590.html'/>

        <xmpp:xep rdf:resource='https://xmpp.org/extensions/xep-0030.html'/>
        <xmpp:note xml:lang='en'>The 'disco' plugin can be loaded to make manual queries.</xmpp:note>
        <xmpp:note xml:lang='fr'>Le plugin 'disco' peut être chargé pour faire des requêtes manuellement.</xmpp:note>
    <!-- And a lot more! -->

        <file-release rdf:resource='https://lab.louiz.org/poezio/poezio/-/archive/v0.13.1/poezio-v0.13.1.tar.gz'/>

It is recommended to start from such an example and tweak it to correspond to your project.

4.2 Extensions Specific to XMPP

As per the requirements, and as you may have seen in the previous example, we want to know the implementation status of each relevant XMPP specification, which isn’t covered by the DOAP specification.

In order to support that, the https://linkmauve.fr/ns/xmpp-doap# namespace defines the <SupportedXep/> element, which sports a few properties:

Table 1:
Property Description Required
xep The URL to the XEP document. Required
status The support status by this project, can be 'complete', 'partial', 'planned', 'deprecated', 'removed' or 'wontfix'. Required
version XEP version implemented by this software. Optional
since Software version this support first appeared in. Optional
note Any implementation note the project deems relevant. Optional

5. Business Rules

A project SHOULD publish the information it deems relevant in the format defined in this specification.

A project MAY maintain this information in another serialisation (JSON-LD, Turtle…), but MUST submit it in RDF/XML serialisation.

Once satisfied with it, a project SHOULD submit their DOAP file to xmpp.org following this process.

xmpp.org SHOULD cache and host the given files on the behalf of projects, so that if their website goes down for whichever reason other consumers can keep working as usual.

6. Internationalization Considerations

Projects with an existing internationalization process are encouraged to use it to translate user-facing strings in the DOAP file.

7. Security Considerations

This document introduces no additional security considerations above and beyond those defined in the documents on which it depends.

8. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [1].

9. XMPP Registrar Considerations

This document requires no interaction with the XMPP Registrar [2].

10. Design Considerations

https://schema.org/ was also considered, given the considerable overlap in features with DOAP, but it didn’t contain many properties useful for software projects. Parts of its properties are reused in this specification, where DOAP was lacking (namely for the logo, screenshot and documentation properties).

AppStream was also considered, but it lacks the extensibility and existing tooling of RDF, while being limited to being a description for software installers instead of a generic software description.


Appendix A: Document Information

XMPP Standards Foundation
Last Updated
Approving Body
XMPP Council
https://www.w3.org/TR/rdf11-concepts/, http://usefulinc.com/ns/doap#, https://linkmauve.fr/ns/xmpp-doap#, https://schema.org/
Superseded By
Short Name
Source Control

This document in other formats: XML  PDF

Appendix B: Author Information

Emmanuel Gil Peyrot


This XMPP Extension Protocol is copyright © 1999 – 2020 by the XMPP Standards Foundation (XSF).


Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Visual Presentation

The HTML representation (you are looking at) is maintained by the XSF. It is based on the YAML CSS Framework, which is licensed under the terms of the CC-BY-SA 2.0 license.

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 <http://xmpp.org/about/discuss.shtml> 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. 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/>.

2. 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 http://xmpp.org/extensions/attic/

  1. Version 0.1.0 (2021-01-26)
    Accepted by vote of Council on 2021-01-13.
    XEP Editor (jsc)
  2. Version 0.0.1 (2021-01-10)

    First draft.