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Protocol for Web Description Resources (POWDER) Working Group Charter

The POWDER Working Group is specifying a protocol for publishing descriptions of (e.g. metadata about) Web resources using RDF, OWL, and HTTP.


  1. Mission Statement
  2. Scope and Deliverables
  3. Duration
  4. Success Criteria
  5. Milestones
  6. Confidentiality
  7. Patent Policy
  8. Dependencies/Relationship With Other W3C Activities
  9. Coordination With External Groups
  10. Communication Mechanisms
  11. Voting Mechanisms
  12. Participation
  13. How to Join the Working Group

1. Mission Statement

The mission of the Protocol for Web Description Resources (POWDER) Working Group is to develop a mechanism through which structured metadata ("Description Resources") can be authenticated and applied to groups of Web resources. This mechanism will allow retrieval of the description resources without retrieval of the resources they describe.

2. Scope and Deliverables

The POWDER Working Group is chartered to specify an RDF vocabulary for specifying authorship of and authentication of Description Resources, a specification for associating a Description Resource with a class of Web resources, predicates for declaring classes of resources based on string functions of the resource URIs, and a protocol for accessing Description Resources.

The POWDER Working Group will base its work on the output of the WCL Incubator Group. In its final report the Incubator Group presents a data model for descriptions and lists 17 open questions. The POWDER Working Group will resolve such questions as are necessary to complete its deliverables. They include how a description for a resource applies (or not) to elements included within that resource (for example, an image in an HTML page), the detail of how to link resources to descriptions, how to resolve any conflicts in the description's data, and several relating to the mechanism for grouping resources ("label scope"). This last area is a vital aspect of the POWDER model but has wider applicability, for example in the Evaluation and Report Language [EARL], P3P's Policy Reference File [P3P] and in the functionality offered by robots.txt.

Once the open questions have been resolved, the major tasks of the Working Group will be to define a generalized method of specifying classes of resources as functions of the URI string as well as other RDF properties, an HTTP-based method of associating metadata with those classes of resources, and the encoding and exchanging of Description Resources. RDF will be the basis for this and the Working Group will produce an RDF Schema or OWL ontology expressing the data model. This working group is not chartered to make extensions to RDF core, neither is it chartered to research the broader development of the Semantic Web. It may, therefore, produce Recommendations that apply RDF and/or OWL technologies using the technique of signing and referencing documents without addressing broader requirements for signing and representing RDF graphs. The requirements to specify classes of resources (grouping, aka 'description scope') should be possible using OWL restrictions and/or some of the SPARQL design. The semantics of description resources will be monotonic; the interpretation of one description resource is independent of other description resources.

Description resources differ in several key respects from other metadata formats of which many are well established. These include data points such as a document's title or a resource's MIME type. Standards such as TV Anytime and ID3 encode metadata about specific resources using vocabularies tailored to specific knowledge domains. Systems such as ISAN provide a look-up mechanism for metadata, again, about individual resources. In each case the descriptive vocabulary and its transport mechanism are bound together and meet a specific need.

In contrast, Description Resources will provide a common representation mechanism that allows anyone to publish a single description, from any knowledge domain, of any number of resources. Such descriptions, whether published by the resource creator or third parties, are subject to authentication and certification, and can therefore be used to build trust in the described resources. This demands that statements can be made about the description as well as the resource being described. Making it clear which is which is a key challenge for the group. The following list is by no means exhaustive but indicates the use cases that create the initial demand for such a system.

  1. All resources on the travel.example.com domain are suitable for display on mobile devices.
  2. All resources on broadcast.example.com/clips are video clips that are suitable for all ages.
  3. All resources on example.com are accessible for all users and meet WAI AA guidelines except those on visual.example.com which are not suitable for users with impaired vision.
  4. Web crawlers are welcome to explore all resources on example.com except those with a path beginning with 'private'.

Other example use cases are included in an appendix to the Incubator Group Report.

It is also noteworthy that the Quatro Project, run under the European Union's Safer Internet Programme, has lead to several implementations of an RDF-based system for a class of description resources. In this regard, use cases are demonstrated by the following 'labeling authorities': ICRA (for child protection), the Internet Quality Agency (for trust and integrity), Segala (for accessibility), and Web Mèdica Acreditada (for medical accuracy).

The POWDER Working Group will review and build on the output of the Incubator Group to deliver the following:

  1. A W3C Recommendation providing a normative encoding of description resources.
  2. A W3C Recommendation describing methods of defining groups of resources.
  3. A W3C Recommendation providing an HTTP-based mechanism for locating and accessing description resources associated with a particular Web resource.
  4. Subject to available resources, the group will develop a description resource validation tool.

Relationship with Previous W3C Work

The W3C PICS Recommendation and the first W3C RDF Model and Syntax Recommendation included a very simple method for grouping resources based solely on a given prefix for URIs. This method proved insufficient for many applications and has been deprecated in subsequent RDF specifications. Other limitations of PICS that are addressed by RDF and by the protocol to be specified by the POWDER Working Group include:

  1. PICS labels are not identifiable by URI. It is therefore difficult to implement systems that build trust in the labels through independent annotation and certification.
  2. PICS does not facilitate linking a resource to an external label. The responsibility for creating content and creating descriptions is typically carried out by different people in large scale organizations. Embedding labels within content does not readily fit this workflow pattern.
  3. PICS pre-dates XML and UTF-8. It therefore has a syntax all of its own and, formally, should be encoded in UTF-7.

The model developed by the WCL Incubator Activity addresses these issues and they will remain an important input to the working group.

Quality Commitments

In its operations, specifications, and test materials the POWDER Working Group will comply with the relevant guidelines of the W3C Quality Assurance Working Group (QAWG).

3. Duration

The Working Group is scheduled to run for 14 months to March 2008.

4. Success Criteria

5. Milestones

The three principal deliverables are all closely interlinked and the Candidate Recommendation stage (i.e. implementations) will require all three to be used. However, the work of the Incubator Group means that the Description Resources Recommendation can be produced more quickly than the other two.

6. Confidentiality

W3C, and all W3C Working Groups, are accountable to the Web community as a whole for the quality of W3C technical work. In support of this public accountability, and to ease cooperation with external bodies, the Working Group makes early working drafts of its documents publicly available.

Feedback and discussion on early drafts will be encouraged on the group's public mailing list (see communications). This charter is also public.

Other email discussions, such as those concerning administrative arrangements, discussions prior to releasing early drafts and reviews of documents from other groups, are accessible to W3C Members only.

All documentation, test suites, and validating tools produced by this Working Group will be publicly accessible.

7. Patent Policy

This Working Group operates under the W3C Patent Policy (5 February 2004 Version).

To promote the widest adoption of Web standards, W3C seeks to issue Recommendations that can be implemented, according to this policy, on a Royalty-Free basis. Consequently, this Working Group will operate on a Royalty-Free basis.

8. Dependencies/Relationship With Other W3C Activities

The POWDER Working Group expects to maintain contacts with the following groups within W3C:

Mobile Web Best Practices

The development of the mobileOK trustmark is an important use case and test case for description resources.

Rule Interchange Format

POWDER has an inherent need for rules to define the scope of a description and for when one description should be used in preference to another. Furthermore, some applications will store user preferences as rules and it it will be beneficial to be able to copy these user preferences between clients.. Cooperation and discussion with RIF is therefore important.

Web Accessibility Initiative (WAI)

The POWDER Working Group seeks close cooperation with WAI on the labelling of resources that meet WCAG guidelines and with the ERT WG on integration with EARL.

Technical Architecture Group

TAG has published a number of relevant findings and POWDER will need to ensure conformance with these. For example the April 2006 finding on Authoritative Metadata.

Semantic Web Deployment Working Group

POWDER will need to draw on this group's expertise and guidance, particularly in relation to the applications of POWDER deliverables outside Description Resources.

Device Independence Working Group

There may be features in common between the protocol for accessing description resources developed by POWDER and a protocol useful for CC/PP. The POWDER Working Group should track future work on a protocol for CC/PP in the Device Independence Working Group or its successor and identify any such opportunities for common features.

XML Activity

POWDER will need to explore non-Semantic Web technologies as alternative approaches to meeting its aims. In particular input will be sought from the XML Query (XQuery) group on the resource grouping Recommendation.

9. Coordination With External Groups

POWDER will seek input and advice from labeling authorities such as ESRB, TRUSTe and BBB Online; and ratings boards such as the MPAA, the BBFC and PEGI.

10. Communication Mechanisms


A public, archived mailing list <public-powderwg@w3.org> [archive], is used to distribute public versions of documents, for public discussion on them, and for other public communications.

A member-only mailing list, <member-powderwg@w3.org> [archive (Member-restricted)], is used to distribute member-only versions of documents, for member-only discussion on them, and for other member-only communications.


The group maintains a public Working Group page...

Phone Meetings

The POWDER Working Group plans to meet every week by phone for one hour.

Face-to-face Meetings

Up to 4 Face to face meetings may be arranged during the 14 months of the charter. The location for each will be decided based on participant preferences but it is expected that they will alternate between US and European locations, tied in with other meetings where possible to minimize expense.

Participation in face-to-face meetings is limited to Working Group participants and individuals invited at the discretion of the Chair to specific meetings, as described in section 3.2 of the W3C Process Document.

Meeting details are made available on the W3C Member Calendar and on the member-only Working Group page.

Communication with the Public

The POWDER Working Group home page is the primary way of communicating the group's progress to the public.

11. Voting Mechanisms

The Group works by consensus. In the event of failure to achieve consensus, the Group may resort to a vote, as described in the W3C Process Document in the section 3.4. All group participants in good standing are allowed to vote.

12. Participation

W3C Staff Resource Commitment

It is expected that this Working Group would consume about 0.3 FTE, including administrative logistics.

External Participant Commitment (W3C Members or invited experts)

For participation in the POWDER Working Group, the requirements for meeting attendance and timely response are described in the W3C Process Document. This participation (attending meetings, reviewing documents, preparing drafts or tools) is expected to consume approximately one day per week.

13. How to Join the Working Group

Information about how to join the Working Group is available on a separate How-to-Join page (Member-restricted).

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This charter is written in accordance with section 6.2.6 of the W3C Process Document.

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