Archives for: 2009

Wednesday, November 25th 2009

Permalink 10:16:38 am, Categories: News

A Final Act

The POWDER Working Group was formally closed yesterday, 24th November, 2009. The WG homepage is now locked and, until and unless another group updates the work, that really is the end of the process. But there were two more things that happened yesterday as well.

First was that the PICS Recommendations were marked as superseded by POWDER. The listing of documents on the Current Status page for PICS now includes links to the relevant up to date documents (not all of which are within POWDER) and each of the Recommendations themselves includes a prominent message that it has been superseded. PICS was a major piece of work right at the very beginning of W3C and many of its features are still apparent within POWDER. A comparison of the two is available separately.

The second event yesterday took place at at the European Commission in Luxembourg: the (successful!) final review for the Quatro Plus project. This project provided much of the impetus for the development of POWDER and it is fitting that these two final events took place simultaneously.

Looking back through the later posts in this blog, I see a glaring omission so let me correct that right away. Many individuals and the companies for which they work contributed to POWDER, many of them over a sustained period of time from initial identification of the problem through to the eventual solution. The danger in listing people is that you forget someone but let me do my best to list correctly the people who have made substantial contributions and/or given critical support at different times during the development process. My personal and sincere thanks to:

  • Shadi Abou-Zahra
  • Dan Appelquist
  • Tim Berners-Lee
  • Tim Boland
  • David Booth
  • Steve Bratt
  • Dan Brickley
  • Jeremy Carroll
  • Kostas Chandrinos
  • Alan Chuter
  • Kendall Clark
  • FOSI
  • Max Froumentin
  • Fabien Gandon
  • Ivan Herman
  • Zeph Harben
  • Vangelis Karkaletsis
  • Cédric Kiss
  • Kazuhiro Kitagawa
  • Kjetil Kjernsmo
  • Stasinos Konstantopoulos
  • Antonis Kukurikos
  • Charles McCathieNevile
  • Libby Miller
  • Pantelis Nasikas
  • Liddy Nevile
  • Diana Penetcost
  • Andrea Perego
  • Addison Phillips
  • Eric Prud'hommeaux
  • Jo Rabin
  • Thomas Roessler
  • Dave Rooks
  • Kai Scheppe
  • Michael Schneider
  • Noboru Shimizu
  • Ghislain Silluame
  • Kevin Smith
  • Ralph Swick
  • Paul Walsh
  • Stuart Williams
  • Matt Womer

And, to the person/people I forgot to mention, my sincere apology.

Now all that's left to do is to exploit the technology. Asked to sum up what POWDER does, for Semantic Web folk I can do no better than to quote Dan Brickley explaining it to Brian McBride: "It solves the About Each Prefix problem." A slightly richer summary of POWDER might be: it allows you apply common RDF descriptions, such as Dublin Core metadata, CC licences, trustmarks and more, to whole groups of resources. It can be processed as XML or OWL (noting a semantic extension) and the output is always regular RDF triples.

Hope you find it useful.


Tuesday, September 1st 2009

Permalink 03:49:18 pm, Categories: News

POWDER is a W3C Recommendation

Phew! It's been a long haul – too long really – but we're there and POWDER is now a recognised Web Standard. We received good feedback from W3C members who reviewed the documents (thank you) and these lead to a couple of trivial – I mean trivial – corrections here and there. What next? The specs are done, the key tools are in place including the validator and two conformant processors (created and maintained by i-sieve Technologies and University of Insubria) as well as the toolkit for using POWDER within a framework like Jena and Pellet. I-sieve has also created a tool for generating mobileOK conformance claims for a Web site using POWDER that also adds in Dublin Core metadata and Creative Commons licences if desired. The QUATRO Plus project that helped to foster the development of POWDER ends this month but the partners are all actively seeking new ways to exploit the work, particularly with trustmarks, aiming to balance the wisdom of the crowds with the wisdom of the experts. Other members of the WG are set to exploit the technology in their own systems with focus on improved search and discoverability. The specs may be done, but there's still plenty of work to do.

Thursday, June 4th 2009

Permalink 06:14:00 pm, Categories: Meeting summaries

POWDER is a Proposed Recommendation

The headline says it all!

See the announcement from W3C.

The W3C membership now has a chance to review the docs and approve (or not) the final transition to Recommendation. As far as the working group is concerned, the specification is complete. Work will continue, of course, on deployment and the development of new applications and community building. Although the specs are done, the work never stops...


Friday, May 1st 2009

Permalink 10:38:06 am, Categories: News

Last Call closed – preparing for Proposed Recommendation

The third Last Call period ended at the start of this week and lead to what amounts to errors being corrected in the IRI canonicalisation sections of the Grouping of Resources document (which was the focus of the call, see implementation experience). A small number of extra tests was added to the test suite to cover this important aspect of matching IRIs against POWDER documents. No changes were made to the Description Resources document or Primer.

The Formal Semantics document was reviewed by the OWL WG and the informative section on expressing POWDER in OWL 2 was subsequently updated. At the time of writing, we're dealing with a substantive comment from Michael Schneider. This is likely to lead to a rephrasing of Section 4.3 but no substantive change that would impact on implementations.

So, once that issue is resolved, the next step is Proposed Recommendation. As flagged previously, we're skipping Candidate Rec stage as we already have plenty of implementation experience to hand.

So is the work on POWDER really over 'bar the shouting' as the phrase goes? i.e. have we done what we set out to do? Let's see.

The charter says: 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. This seems well covered!

The charter gives specific examples of statements that must be expressible in POWDER:

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

The first two are exemplified in the documents published by the group (see mobileOK and ICRA examples). The other two could easily be encoded in similar fashion using suitable vocabularies.

The charter sets out specific deliverables:

  1. A W3C Recommendation providing a normative encoding of description resources (we refer to it internally as 'the DR doc').
  2. A W3C Recommendation describing methods of defining groups of resources (referred to internally as 'the grouping doc).
  3. A W3C Recommendation providing an HTTP-based mechanism for locating and accessing description resources associated with a particular Web resource (see Section 4 of the DR doc).
  4. Subject to available resources, the group will develop a description resource validation tool. Done! (along with several other tools).

The charter also calls on the group to resolve the open questions raised by the Web Content Label Incubator Group: a previous blog entry covers that, which just leaves the requirements derived from the use cases. An exhaustive re-listing of the requirements and how they're covered would make a very dull and largely pointless blog entry but I'll pull out a few for special mention.

3.1.8 Reference

It must be possible for a DR to refer to other DRs or other sources of data that support the claims and assertions made. This is possible through the certified and supportedby terms discussed in Sections 5.2 and 5.3 of the DR doc. This also covers 3.2.4 Link to Test Results where the requirement is to be able to link to test results (perhaps encoded in EARL).

3.1.9 Standard Vocabularies

There must be standard vocabularies for assertions about DRs. Actually we kept the vocabulary to a minimum (i.e. reused existing ones as far as possible). However, terms such as issuedby, issued, validfrom and validuntil were introduced. issuedby caused particular debate as it is so close to terms in both the FOAF and DC vocabularies – but which one to support? Can we not support both? Which is the 'stable standard?'. Cue a lot of e-mails and discussion!

3.1.10 Identity

DRs, their components and individual assertions should have unique and unambiguous identifiers. Actually we haven't done this as such. POWDER documents have URIs and you can give individual descriptorsets identifiers but, largely due to RDF's lack of (formal) support for named graphs, each component of a DR does not have an identifier. Furthermore, we deliberately made sure that classes in POWDER-S documents typically had node IDs that can't be referenced externally so as to avoid assertions being added to those classes from external sources.

3.2 Fitting in with Commercial or Other Large Scale Workflows

This requirement — actually a heading for a whole set of requirements — is at the heart of the operational/semantic split. POWDER has to be as easy to use in a commercial, practical environment as possible. Hence the XML encoding and, in particular, the ordered lists of DRs through which we meet requirement 3.2.3 Default Description.

Unless something goes wrong, we should be ready to begin the transition to Proposed Recommendation process next week (or the week after as a worst case).

We really are nearly there.


Monday, April 6th 2009

Permalink 09:54:52 am, Categories: Meeting summaries

The What and Why of the Third Last Call

Since making our second Last Call for comments at the end of last year we've responded to all of them and have been completing work on the tools - the processors, the XSLTs and so on - all of which has now been done.

So why aren't we at PR yet? There are a couple of reasons for this. There has been an ongoing battle between (WG member) Stasinos Konstantopoulos and (W3C team member) Eric Prud'hommeaux over whether the POWDER Semantic extension applies to the data layer or the application layer. The two protagonists have agreed to differ whilst the document has gone forward.

The second issue that has arisen concerns the other area that has prompted a lot of comment - the canonicalisation section of the grouping doc. Despite many changes over the last year or so and input from the Internationalisation WG, (W3C team member) Thomas Roessler spotted more problems with this section.

After a lot of e-mail bouncing around on, I'm sorry to say, a team-only list, I had a long conversation with Thomas and (Semantic Web lead) Ivan Herman. Some context:

The Semantic Web (RDF, OWL, SPARQL etc.) is written solely about URIs, not IRIs. Furthermore, all URIs are opaque strings - they have no meaning. This goes back to Jeremy Carroll's useful distinction between "" and <>. In other words, for RDF etc. our issue of processing URIs/IRIs as meaningful strings doesn't arise.

IRIs - that is, URIs written in things like Cyrillic script, Japanese Kanji etc. - are going to be more important in the coming 12 - 18 months (according to Thomas who, among other things, represents W3C at ICANN and so has a good grasp of such things). For POWDER not to be useful now and in the near future across all parts of the Web would limit its potential usefulness.

As we have discovered, the encoding of IRIs and International Domain Names is less than clear. However, there is a recognised path to take in this area which involves converting IRIs into ASCII - essentially converting IRIs to URIs.

It is not the POWDER WG's job or wish to solve the whole issue, neither is it within our ability to do so.

The POWDER to POWDER-BASE transform XSLT doesn't do any of the canonicalisation stuff, and it would be hard, if not impossible for it to do so. Therefore, strictly speaking, some form of pre-processing is already necessary before the XSLT is applied (the Perl script does do the canonicalisation but now needs a bit of work).

Given all of the above, the group was faced with a choice between either making significant edits in all its documents to talk only about URIs or, as we have done, further amending the canonicalisation section to introduce the ToASCII function as defined in RFC 3490. It is this change that has prompted the new Last Call announcement, open until Monday 27 April. The documents published on 3 April to coincide with the Last Call reflect all the changes made following comments received in the previous calls and, with the exception of the highlighted sections of the Grouping of Resources document on canonicalisation, are considered stable.

One important, although editorial, change worth highlighting is in the Description Resources document. The definition of the describedby relationship type and the two POWDER Content Types is much improved. describedby is now included in the IANA registry of ATOM Link relationship types.

The Test Suite has been significantly updated in the 3 April version and is now unlikely to change significantly (we may add some new tests for the canonicalisation section). Perhaps rather perversely, the test suite does include a test for the informative section on HTTP Link. The Primer is considered stable and very unlikely to change further.

Minor adjustments to the POWDER Processors are in progress and, notwithstanding changes prompted by the last call, the group is expecting to go to Proposed Recommendation in May.


Friday, January 16th 2009

Permalink 02:21:41 pm, Categories: Meeting summaries

Situation Report 16 January 2009

The group's charter expired at the end of December so we're in something of a state of limbo (one might say unchartered territory). However, a lot of work is being done to get us ready for a request for transition to PR. The links below are all very much temporary but they are all up to date and reflect the true status of the group's work (the homepage and published documents are not being updated at the moment). Several tools are done and dusted:
  • The Validator. This is expected to move to in due course
  • Perl-based processor. Again, this should move to a new home soon. There are minor improvements to make but it implements POWDER.
  • Semantic Processor. This is not a complete application, nor is it a conformant POWDER Processor, but is a command line-driven exemplar of POWDER-S. It uses Jena and Pellet to return descriptions of a given URI based on a given POWDER-S document.
Tools have also been produced that implement the transformations defined in the Formal document. An implementation report is being maintained. The POWDER XML Schema is also being debugged. Again, it's almost there. Actually, there are several interlinked schemata to handle POWDER and POWDER-BASE. The GRDDL transformation links will be included when we next make these available. A second, more sophisticated POWDER processor is close to completion. Based on PHP, it uses the schema to validate POWDER documents (the Perl-based processor uses the same code as the validator). Finally, most of the documents have been updated. It would be improper to link to them here but if you want to see updated versions of the DR, Grouping and Formal docs, plus the Primer and Test Suite, please get in touch and I'll send you the URIs. We're nearly there. Thankfully.
Permalink 01:56:05 pm, Categories: Meeting summaries

Resolution of Open Questions from the Web Content Label XG in POWDER

The POWDER WG was formed following the Web Content Label Incubator Activity (WCL-XG). In its final report, the XG noted a total of 17 Open Questions, all of which have been resolved by POWDER. Note that cLabel was the term used in the XG: the equivalent term in POWDER is Description Resource (DR)

OQ 1:It is an open question whether there may be a requirement for some forms of cLabel that involve editing those resources.
The use cases presented do not call for DRs to be embedded within the content they describe. On the contrary, the expected use of POWDER strongly suggests that DRs should always be separate.
OQ 2:Should WCL-XG be successful in securing a WG charter, the abstract model for resource grouping will itself come under full scrutiny with a view to its publication either as a WG Note or a full Recommendation in its own right.
The abstract model developed in the XG is the basis for POWDER: Description Resources (a recommendation track document).
OQ 3:The mechanism for exposing properties of resources should by preference be both standard and be cLabel based. However, the precise workings of this have not been examined and are for further study.
The mechanism is fully developed in POWDER.
OQ 4:If successful in securing a WG charter, the group will need to address how to resolve situations in which scoping statements do not match.
The WG has taken the view that it is not practical to make it impossible for DR authors to create scope statements - now called IRI sets - that do not conflict. The Outline Methodology section of the Grouping document together with the short section on the safe use of regular expressions make it clear that mistakes are possible. A simple to use tool has been created to allow DR authors to develop and test their IRI set definitions.
OQ 5:It is an open question as to whether access to label repositories should be governed by a standard protocol.
OQ 6:It is also an open question as to whether a repository should provide a bulk data transfer capability alongside whatever capabilities it offers for transfer of description, cLabels and packages.
Open Questions 5 and 6 are covered by Section 4.4 of the Description Resources document.
OQ 7: HTTP Link Header
The group has been active in promoting the reinstatement of the HTTP Link Header and in the discussion surrounding the registration of relationship types. The relevant Internet Draft is very likely to reach RFC status during the first half of 2009 - shortly after the anticipated time when POWDER will become a Recommendation. The WG therefore has retained discussion of HTTP Link in its documentation but has flagged the relevant section as informative.
OQ 8:The form of authentication and certification mechanisms for cLabels requires further study.
This remains true - however, such a study is to be carried out by the individual labelling authority such that an appropriate mechanism for the particular application is implemented rather than demanding a single 'one size fits all' approach. POWDER provides a number of features designed to allow various authentication methods.
OQ 9: There is also work to be done to more clearly define the roles of various players in the trust chain, such as labeling authority, certification provider etc.
Section 5 of the Description Resources document discusses several different trust models that might be applied to POWDER.
OQ 10:It is not clear how labels on transcluded elements relate to any labels on the content that initiates the transclusion.
The word 'transclusion' was misused here, however, it is the nature of HTTP and RDF that each description of a resource is made and processed separately. Therefore, elements within an HTML page may well have different descriptions from the page itself. DR authors should be aware of this.
OQ 11:It is not clear whether it is useful or necessary to identify individual portions of content and to assign them individual labels, or to be able to provide labels that refer only to the resource without any transclusion.
It was resolved that fragment identifiers would not be part of the grouping mechanism. However, they may be supported in the extension mechanism as discussed in Section 2.1 of the Grouping document.
OQ 12:It is also not clear how redirection of HTTP requests affect the interpretation of a cLabel that refers to the non-redirected URI but does not refer to the result of redirection.
This was resolved in relation to the conformance criteria for a POWDER Processor which SHOULD NOT, where IRI1 is in scope of a given DR and dereferencing it redirects to IRI2, automatically treat IRI2 as also being in scope of that DR.
OQ 13:It is not clear how the requirement that each cLabel must have a unique identity, so any modification to it, such as renewing its validity period, will result in the creation of a new cLabel, with a new URI fits in with the operation of large scale workflows, which cannot easily accommodate changes in associations between content and their labels, and consequently this is for further study.
This is covered in the Primer which advises the creation of a 'latest version' link which would redirect to the appropriate POWDER document.
OQ 14:On a related note, the group discussed the relationship between the validity of the label and the cache headers that may be attached to it, but came to no clear conclusion on this. One suggestion is that clients should not be required to use the valid-until date in a cLabel to decide whether to fetch the resource. LA's would be encouraged to use HTTP response cache features, e.g. by setting Cache-Control: max-age to correspond to the appropriate valid-until date.
This issue was resolved and is discussed in Section 5.2 of the Description resources document.
OQ 15:[This section is subject to further review and elaboration - e.g. which terms are mandatory, which are optional, how to provide a unique identifier for the vocabulary. Note also that some of the terms suggest that labels can be altered, and there is an open question as to whether this is in fact possible, given that each instance of a Content Label must have a unique and unambiguous ID. Equally it is important that when a label is 'renewed' that it is not then necessary to change all references to it. It may be possible to work around this by accessing labels by 30x redirection, but the rules applications would be required to follow remain to be discussed ]
The POWDER-S vocabulary is fully defined with a namespace document at It is a minimal set of terms and classes that can be built on to suit different application environments.
OQ 16:If successful in securing a WG charter, WCL will need to define additional terms for certifying labels. Also, it may be possible to define tests for some of the vocabulary terms.
See Section 5 of the Description Resources document.
OQ 17: If successful in securing a WG charter, WCL would seek to:
— Produce a normative encoding of the WCL model in RDF. This would, of course, take into account any changes made to the model made by the WG itself. The discussion would be likely to include sample SPARQL queries etc. and guidance on making data available for property-based resource grouping.
— Show examples of cLabels encoded using RDFa.
— At least sketch encoding cLabels entirely in XML.
All of these features are present. The Description Resources document encodes the WCL model in both XML and RDF and includes an example of linking to a DR using RDFa. Sample SPARQL queries are provided in the Section 5 of the Formal Semantics document.

Having conducted this review, the working group therefore contends that the open questions posed in the incubator group have been answered.

Phil Archer,
16 December 2008.

Permalink 01:53:22 pm, Categories: Meeting summaries

Meeting Summary 15th Deceember 2008

The group has now completed its work in terms of defining POWDER. The group is concerned with making sure all the documents are polished and ready for transition to Proposed Recommendation and that the various tools properly implement the different features. An implementation report will be compiled in the coming days. Other documents showing that comments have been answered and issues resolved will also be finalised. The Christmas holiday means it's unlikely that the group will be able to seek transition to PR before the end of the year but will do so in the first working week of 2009. For now the good news is that the weekly telecons are done!