RDFa Task Force -- 23 Oct 2006

... Also, we've submitted a WWW2007 RDFa workshop proposal

Ben: reminder; we've targetted 27 Oct as date for code and examples of new syntax

ACTION: Elias start an FAQ [recorded in http://www.w3.org/2006/10/03-htmltf-minutes.html#action10] [IN PROGRESS]

Elias: just started it

<EliasT> ... http://esw.w3.org/topic/RDFa#FAQ

Reification

Mark: my impression after the discussion was that some of the problems were due to reification in a particular context
... for what RDFa needs, the issue seems more clear
... e.g. 'who said X' does seem to be clear
... in the references that Elias cited
... Dan's point is that he wants RDFa to be no more expressive than RDF/XML
... so that all RDFa can be transformed to RDF/XML

Elias: I don't agree that it is clear how we can identify a triple

Mark: if it's not clear how to do this in RDF/XML then we don't need to do it in RDFa

Elias: by 'identify' I mean know whether it exists in a specific named graph
... it's not clear how to say 'that triple'
... the RDF spec is clear that reification is about identification, not about quoting
... but we don't have a clear way to identify

Mark: but if RDF/XML hasn't solved the problem then RDFa can't solve it either

Elias: but we have documents

Mark: we can name some other type of Statement but we can't name an RDF triple
... if we wanted to, we could say there is an xyz:Statement that has implicit information
... but we'd still need some magic if there's no way to say that this maps to an rdf:Statement

Elias: RDF reification does not say that if you have the quad it implies the triple

Mark: in terms of generation from RDF/XML that's the case
... you're not supposed to assume that the original triple exists
... but that doesn't prevent the other way around
... RDFa could say the triple exists

Ben: we can start with some RDFa and specify what it means in RDF/XML

<EliasT> Note that asserting the reification is not the same as asserting the original statement, and neither implies the other. That is, when someone says that John said something about the weight of a tent, they are not making a statement about the weight of a tent themselves, they are making a statement about something John said. Conversely, when someone describes the weight of a tent, they are not also making a statement about a statement they made (since they may

^excerpt from RDF spec

Ben: but we can say that the dc:creator of the s/p/o quad is responsible for a triple asserted by that quad

Elias: we want to attach provenance to HTML documents, not to graphs

Ben: we know how to do that
... e.g. a LINK or a META on a DIV can say who is the creator of that DIV

Mark: even without reification there is a question
... on the one hand you're making statements about the DIV
... on the other hand we're reusing it at a higher level to represent a bnode

Ben: but the bnode is just a local concept

Mark: to be consistent, the only thing you'd be making statements about is the DIV

Mark: similar issue to describing the car or the web page that describes the car

Elias: given a div with two classes, can we say that the two type statements were made by different creators?

Ralph: that seems a corner case

Mark: when we embed metadata in the document rather than have it standalone then we lose the ability to attach provenance to the metadata

Ben: we could add more to reify the class="foo bar" case if we really wanted to

Ben: that would be one way to think about it but this is still more than RDF/XML gives
... but another way is to simply write the triple two times

Mark: 2 choices; 1. use reification as it is
... we've agreed that you can't connect between the asserted triple and the quad
... 2. say that the "RDF-ness" is not really in the document; explode the document, expand every property in the document so that the contents are all objects, etc.
... then this exploded version is converted back 'down' to RDF/XML
... method 2 makes things quite complicated

Elias: even if we go with method 1, there is still the question -- adding provenance to a DIV adds statements to multiple triples
... and that DIV could become the object of some enclosing element

<EliasT> .. reification ...

Elias: if our granularity is the XML element the reification applies to two different things

Mark: I could just about live with this
... but in the IPTC case, given the statement "Reuters says this article is about skiing. Reuters is 80% confident in this categorization."
... and separately "BBC says this article is about skiing. BBC is 60% confident in this categorization."

Ben: but this is an RDF problem too

Elias: if rev="bar" was added later by a different person than rel="foo" ...

Ben: you're talking about multiple authors changing the same piece of HTML

Elias: don't confuse two things; an HTML element and ...
... the HTML element can create many triples

Ben: I can understand that attaching a link to a DIV is attaching the link to every triple
... this may not be the best practice, but that _is_ what the HTML says

Elias: Reuter's 80% confidence is not in the statement itself but that the category is skiing
... if I add iptc:joke to the categories, the 80% should still only apply to skiing

Ben: but why do we need to support that?

Elias: I am also worried about the case where the LINK element participates in an enclosing rev property

Ben: we need to look at some tricky examples give this new proposal and make sure they turn out sort-of reasonable

Mark: now I'm having trouble seeing these examples as reification
... I am reevaluating my earlier comments suggesting that n-ary relations were not what we wanted
... the category/confidence example can be done with n-ary relatoins
... IPTC used a LINK element to add a confidence
... perhaps a way out of the provenance issue is to handle it at the HTML level
... use an additional HTML element rather than adding properties [to an existing one]
... I'm starting to see that an n-ary solution fits more cases than I'd originally thought
... I will extract more examples from original IPTC documents

ACTION: Mark produce more examples of applicability of n-ary relations from IPTC documents [recorded in http://www.w3.org/2006/10/23-htmltf-minutes.html#action08]

ACTION: Elias to send by email examples of HTML markup that could be problematic with reification [recorded in http://www.w3.org/2006/10/23-htmltf-minutes.html#action09]

<EliasT> http://www.w3.org/TR/swbp-n-aryRelations/#useCase1

<Steven> http://www.w3.org/People/Ivan/

RDFa Task Force

23 Oct 2006

Attendees

Contents

Action Item Review

Reification

Summary of Action Items