POWDER Working Group Blog

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.

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 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'.

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.

POWDER Outreach Event More of What You Want When You Want It This was the third and (probably) final outreach event organised by the POWDER Working Group. Hosted by Yahoo!, who have long been interested in the concepts around machine-readable trustmarks through this working group and the Quatro Project which is part of the EU's Safer Internet Programme, the event had a healthy WG member/guest ratio. As with previous occasions, the event was held under the Chatham House Rule which means that reporting is restricted, however, it is safe to say that our guests included TRUSTe, Mpower Media, the MPAA, Secure Path, AT&T, Cable in the Classroom, the Center for Media Literacy, Comcast and more. The working group's output and ideas were well received with several expressions of support. The discussion, naturally, focussed on the issue of trust. Can a machine trust a machine? As POWDER makes clear, the answer to that is no. Trust is a judgement of one person by another – what POWDER does is to facilitate that human judgement. Several organisations in the room made it clear that they are actively looking at implementing POWDER in one way or another, either as a full-blown service or as a test bed. Various group members discussed their own implementation plans and, whilst no one would suggest that there is anything other than a great deal of work yet to do, future adoption of the protocol seems set for a good start. As for adoption by the big search engines - it's clear that if and when there is sufficient POWDER data of sufficient quality (i.e. without spam), then they will be pleased to use it. Any future effect of POWDER on things like position in search results will emerge rather than be announced.

A little late due to holidays, here's the blog entry I've been hoping to write since about last November - we've reached Last Call! The group is producing a total of three Recommendation Track documents and Last Call comments on these are welcome through to 14th September. The Grouping of Resources document is the oldest of the three and has retained much of its original character from 2007. A critical aspect of POWDER is the ability to define groups (actually now we talk about IRI sets but it's the same beast). The Description Resources document has been through the most substantial changes since its early days although the first example in the document doesn't look so different from the first public working draft version (published nearly a year ago). It's the division between operational and formal semantics, introduced this year, that is the big change between the first and this Last Call version. The development of the two-version approach (operational and formal semantics) lead to the creation of the Formal Semantics document which underpins the other two. This is the one that defines the semantic extension required to make POWDER work in an OWL/RDF environment and confers membership of a class on an IRI if it matches one or more regular expressions. A couple of issues are worth highlighting. Firstly the Description Resources document supports the re-instatement of the HTTP Link Header as proposed by Mark Nottingham. This also impacts on the wider debate about how @rel values should be managed. Mark Nottingham's Internet Draft makes one suggestion but there are other ideas circulating and the way forward is not 100% clear. It is largely this debate that causes us to flag the recommendation of HTTP Link as a feature at risk. In the Formal Semantics document we note a further feature at risk, namely the ability to include arbitrary RDF in a POWDER document. There are strong arguments on both sides and the group will make a resolution based on Last Call comments received. Alongside the Recommendation Track documents, the WG is pleased to publish drafts of its Primer and Test Suite. These will continue to evolve as the group works through Last Call and Candidate Recommendation phases. Finally, the group has announced its latest outreach event. Called POWDER: More of What You Want, When You Want It, the event takes place at Yahoo!'s Mission College Campus in Santa Clara on 16th September.

The group met in Boston with the aim of advancing its draft documents to Last Call… er… it didn’t quite go that way. However, the overall news is very positive. A problem that has dogged the development of POWDER since even before the establishment of the WCL Incubator Group appears to have been solved. Expanded upon by Dan Brickley during the XG process, it comes down to the fact that we want to make generalised statements about lots of resources at once when RDF is predicated on triples with a single resource, identified by a URI, as its subject. It has been suggested before that OWL might provide a way forward but a clear notion of how this could help has been as elusive as any other solution. Now we think we know – and it has the air of ‘is it really that simple?’ about it. The benefit of a gathering like TPAC – indeed the whole point of the event – is that you can ask other people what they think. So in the corridors and restaurants of the conference hotel views were sought from the likes of Eric Prud'hommeaux and David Booth with Dan Brickley being the recipient of a lot of IM traffic. But it was during the first day of the WG meeting that we were very pleased to be joined by several ‘observers’ including Max Froumentin, Fabien Gandon and Tim Berners-Lee. This was just the kind of input the group needed – although it felt a bit like anaesthesia-free surgery at the time. It was the next day when we were able to analyse all the input we’d received, begin to identify aspects that require further elaboration… and to work out a new timeline. The new model is best described using an example – that we want to assert that all resources on example.org are mobileOK. We first define the set of all things that are mobileOK (actually, we don’t – that’s the job of the Mobile Web Best Practices Working Group but you get the idea). Then we define an OWL class with the property restrictions that apply to the resources to be described, in this instance, resources that have the property of being available on example.org. If we now assert that the class of resources on example.org is a subclass of the class of resources that are mobileOK, OWL inference can tell us what we need to know. Recall that we always start with a particular candidate resource in mind, say, http://www.example.org/index.html. Is that an instance of the class of resources on example.org? Yes. What do we know about it? Well… now we know it’s mobileOK. But hang on, what about attribution? As the WG members emphasise over and over again, the absolute critical factor in POWDER is that you always know who has made the assertion that a particular thing is true. You can’t decide whether you trust an assertion if you don’t know who’s making it. A classic job for reification! Defining a class of things that are mobileOK is uncontentious, as is defining a class of things that are on example.org. The triple in which trust is important is the one that says that the example.org class is a sub class of the mobileOK class – so that’s the one that will be the focus of the reification data with our usual foaf:maker, dcterms:issued and wdr:validUntil properties. In the week following the meeting, some basic testing will be carried out at NCSR Demokritos in Athens, after which we’ll be able to put such examples online. Meanwhile all currently published documentation (i.e. anything published before November 8th 2007) must be treated with extreme caution – the forthcoming revisions are very substantial. A few further notes:

1. The group must make significant efforts to engage with, and seek input from, the OWL community.
2. We need to try to make sure it is always clear when creating a Description Resource which class is a sub class of the other.
3. We will be doing a lot of testing to ensure that standard OWL reasoning does always produce the desired outcome (expect a full Test Suite as part of the POWDER document set).
4. Description Resources are about adding semantic data to the Web and all the normative documentation will be couched in Semantic Web terms. However, we do expect to be able to devise an XML-based approach that can be used to model simple DRs. The structure of such an XML instance will look superficially similar to the example DR in the current documentation and it will be possible to use a GRDDL engine to generate a DR from it.
5. There was some discussion about ‘the protocol part’. We expect to just use rel="meta" (cf. rel="powder") on link elements and need to look at services that can return triples about whatever resource includes such a link plus a triple pointing to the full DR data.
6. Tim BL in particular was concerned about the effect on processing efficiency of using things like ‘path contains’ and regular expressions to match against URIs in the Resource Grouping side of things. The group will take this into account in the light of the use cases for POWDER, however, as a first pass, we remain of the opinion that such flexibility is important, even if DR creators are encouraged to only use such features when absolutely necessary.
7. The group’s timeline has clearly slipped. We’re now planning to reach Last Call by the end of January with test suites completed, LC comments answered and the Primer finalised around the end of April (so we can seek transition to Proposed Recommendation). We plan to hold at least one outreach meeting in the Last Call phase (see previous event).
8. It follows that we expect to apply for a relatively small charter extension of 3 months to give us to the end of June to complete our work.