Archives for: November 2007

Monday, November 26th 2007

Permalink 05:06:56 pm, Categories: Meeting summaries

Meeting Summary: 19th November 2007

The bulk of the meeting was taken up with a discussion of the 'new model' sketched out at the face to face meeting in Boston (see previous blog entry) and the follow up work done, particularly at NCSR. The group is aware that, at present at least, it does not have the necessary skills to work comfortably with OWL, rule languages and inferences. The model of defining a class of all things that are of a certain type (say, mobileOK) and then a class of things that are on a given Web site (say example.org) and then making the statement that "ACME testing says that the set of resources on example.org is a subset of the resources that are mobileOK' makes sense and can be conveyed in text and images, but rules are much more specialised and harder to work with for the non-expert. Since it is anticipated that it will be non-experts that create and work with DRs, this is a substantial problem. Machine processability is very important - Description Resources have to be machine processable. The question is how much manual work is acceptable or, at least, how much specifically POWDER processing is acceptable? This will be explored on the mailing list in the coming days and weeks. The group ended with some housekeeping issues concerning the timing of its weekly calls and the date for its next face to face meeting, provisionally scheduled for mid January in Athens. Finally there was a brief discussion about the rel="powder" issues. Observers at the face to face meeting suggested that rel="meta" was what we should use and furthermore, that any user agent following such a link should expect to receive back triples about that resource. This is something the group will return to in due course but it looks as if rel="powder" is probably not going to be necessary.
Phil ARCHER

Saturday, November 10th 2007

Permalink 03:22:53 pm, Categories: Meeting summaries, News

Summary of Face to Face meeting held during TPAC, 8 – 9 November 2007

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.
Phil ARCHER 2 comments

Thursday, November 1st 2007

Permalink 09:16:32 am, Categories: Meeting summaries

Meeting Summary 29 October 2007

The meeting began with a quick tour of the latest version of the Grouping of Resources Document followed by a resolution for this to be published as our next working draft (TBA on this blog). There was then a discussion of the new use accessibility-centric cases that have been developed since receiving input from Liddy Nevile. Two revised use cases will replace the current use case 2.1.5. While looking at the Use Cases document, two further issues were discussed. Firstly requirement 3.3.4 Compact says: It must be possible to express DRs in a compact form. As pointed out by Dan Connolly, this is un-testable and therefore is to be dropped. A further requirement, 3.1.9 Standard Vocabularies says 'There must be standard vocabularies for assertions about DRs.' This has not been addressed yet and therefore it was resolved to create a new RDF property of wdr:certifies to provide such a standardised way of creating the certificate shown in section 6.2 of the current Description Resources draft. It was noted that the use of wdr:certifies and wdr:certifiedBy are independent of each other - i.e. using one does not entail using the other - although it's probably a good idea to do so. [Looking at the example now, it seems that wdr:certifies shouldn't be a property, rather it should be a sub Class of Descriptors]. This raised the issue of whether the grouping document should support definition of resources by reference to a hash of them so that a DR could indicate that it only applied to resources if they have remained unchanged. A proposal will be made to the group on this issue shortly (should we specify a limited number of hash types, such as with wdr:sha-1 or a more generic wdr:hash with a separate wdr:hashAlgorithm predicate?) The chair reported on the recent establishment of the HTTPBIS Working Group at the IETF and the statement in the charter: "The WG is not tasked with producing new methods, headers, or extension mechanisms, but may introduce new protocol elements if necessary as part of revising existing functionality which has proven to be problematic." On present evidence it seems unlikely therefore that the HTTP Link Header will be standardised although this working group would support such a move. The normative POWDER documents will not refer to usage of the HTTP Link header, however, informative documents will (because it's very useful and works!). The meeting closed with a realistic expectation of announcing Last Call on its Rec Track documents following the face to face meeting in Boston 8 - 9 November.
Phil ARCHER