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RE: Building a bridge from RDF to the web?

From: Thompson, Bryan B. <BRYAN.B.THOMPSON@saic.com>
Date: Tue, 25 May 2004 09:29:57 -0400
Message-Id: <D24D16A6707B0A4B9EF084299CE99B39053F8BFD@mcl-its-exs02.mail.saic.com>
To: "'Seaborne, Andy '" <andy.seaborne@hp.com>, "'Thompson, Bryan B. '" <BRYAN.B.THOMPSON@saic.com>, "'''public-rdf-dawg@w3.org' ' '" <public-rdf-dawg@w3.org>

Andy,

I'm not suggesting that we invent a new transform language, but that
we make sure that the existing transform languages can be effective
consumers of the results of a DAWG query.

-bryan

-----Original Message-----
From: Seaborne, Andy
To: Thompson, Bryan B.; ''public-rdf-dawg@w3.org' '
Sent: 5/25/2004 9:17 AM
Subject: RE: Building a bridge from RDF to the web?



-------- Original Message --------
> From: Thompson, Bryan B. <mailto:BRYAN.B.THOMPSON@saic.com>
> Date: 25 May 2004 13:54
> 
> Andy,
> 
> I think where these examples fall short is that they presume a query
> approach rather than assuming some sort of abstract model of variable
> bindings for a result set.  The first example is using a path model,
> which is troubling given the syntactic freedom of RDF/XML and given
> the opportunity to deliver a response in N3 or other notations.

Actually Treehugger is not dependent on the serialization.  The path is
a
path in the abstract syntax - the graph.  Damian happens to have choosen
a
path-syntax that is like the stripped syntax as he is interested in FOAF
data particularly.  It interfaces the graph to Saxon.

Why not ask Damian in rdf-interest?  (and he reads the DAWG list :-)

>            The
> second example presumes that we are using a specific query language
> with looping constructs into which we can embed the XML that we want
> to generate.

I'm not sure why the looping constructs are a problem.  XQuery is
decalrive
so a processor isn't constrained to execute the XQuery script as a
program.
XSLT has loops.

> 
> What I have in mind is that variable bindings are generated by a query
> against the RDF data model -- and that those bindings should expose a
> (cannonical) abstract model of the query response SUCH THAT an XSL
> processor can consume those bindings and people can reliable match
> on the contents of the bindings in order to generate XML.  Much in
> the same way that XSL and XPath are connected by the notion of a
> "node set" which is generated by XPath and consumed by XSL.

If we aren't inventing a new transform language, we have to interface to
whatever the existing tools.  If we were inventing a new transform
language,
we would have that freedom.

> 
> Maybe I am off base, but I guess the question is "If variable bindings
> are the interface into the query result that we expose to the client,
> can the client successfully use that interface to generate arbitrary
> XML?"
> 
> -bryan
> 
> -----Original Message-----
> From: Seaborne, Andy
> To: Thompson, Bryan B.; ''public-rdf-dawg@w3.org' '
> Sent: 5/25/2004 8:27 AM
> Subject: RE: Building a bridge from RDF to the web?
> 
> 
> 
> -------- Original Message --------
> > From: Thompson, Bryan B. <mailto:BRYAN.B.THOMPSON@saic.com>
> > Date: 25 May 2004 13:13
> > 
> > Andy,
> > 
> > You wrote:
> > 
> > > If that bridge is a way to extract information from RDF models and
> > > get it into both XHTML (for people) and XML (for people and for
> > > web services), then I agree with you.
> > 
> > Variable bindings certainly seem to be a good place to start in
order
> > for the client to be able to avoid posing the query twice - once to
> > the RDF store and once to the identified sub-graph (and possible
using
> > a different kind of query interface altogether!)
> > 
> > So, can you outline for me how you see that variable bindings
exposed
> > by a DAWG protocol could be exploited by an XML Stylesheet so as to
> > generate, e.g., an XHTML document?
> > 
> > -bryan
> 
> Rather than an on-the-fly design, how about from the examples of
systems
> that have tried this:
> 
> ---------------------
> 
> From: http://rdfweb.org/people/damian/treehugger/introduction.html
> Treehugger example:
> 
> <xsl:for-each
>   select="./rss:items/rdf:Seq/rdf:li/rdf:Resource">
>      ...
>      do something with each member of the sequence
>      ...
> </xsl:for-each>
> 
> A path is Treehugger is property/class/property/class - I prefer a
> property/property/property path but that isn't relevant here.
> 
> So make/replace the "select" attribute be a graph pattern.  Need to
cope
> with multiple variables in the query string.
> 
> ---------------------
> 
> From Jonathan Robie's talk:
> http://www.w3.org/2004/Talks/tp-robie/slide4-0.html
> 
> declare namespace rdf = "rdf.tagsalad.org";
> 
> for $artist in
rdf:instance-of-class(rdf:predicate-domain("c:creates"))
> let $artifact := rdf:join-on-property($artist, "c:creates"),
>     $museum := rdf:join-on-property($artifact, "c:exhibited")
> return
>     <result>
>        <artist>{ $artist }</artist>
>        <artifact>{ $artifact }</artifact>
>        <museum>{ $museum }</museum>
>     </result>
> 
> ---------------------
> 
> Can one write in Xquery:
>    $var1 $var2 := someQueryFunction("graph pattern")
> If so, then this would be a more compact form.
> 
> Bryan - is this what you had in mind?
> 
> 	Andy
> 
> 
> 
> > 
> > -----Original Message-----
> > From: Seaborne, Andy
> > To: Thompson, Bryan B.; 'public-rdf-dawg@w3.org'
> > Sent: 5/25/2004 6:39 AM
> > Subject: RE: Building a bridge from RDF to the web?
> > 
> > > From: Thompson, Bryan B. <>
> > > Date: 24 May 2004 20:49
> > > 
> > > One of the issues that became clear to me during the recent WWW
> > > meeting in NYC is that we are missing a bridge between the RDF
model
> > > and XML. In particular, people who are going to be using the
> > > semantic web need a bridge from the RDF data model to application
> > > specific XML vocabularies (actually, we need one that goes the
> > > other way also, but that is, I think, a seperate question). 
> > > Perhaps the most common use case is querying an RDF resource and
> > > using the results to drive an XSL Transform, which in turn might
> > > generate XHTML. 
> > 
> > If that bridge is a way to extract information from RDF models and
> > get it into both XHTML (for people) and XML (for people and for web
> > services), then I agree with you.  There isn't going to be one such
> > form for presenting information extracted from RDF so tools such as
> > XSLT and XQuery seem to be the toolsets to use.
> > 
> > There has been some work on this: Rob outlined the use of XQuery and
> > OWL data, and it reminded me of Jonathan Robie's presentation [1] at
> > Cannes this year.  The important aspect here is that access is to
the
> > abstract graph, not the RDF/XML syntax.
> > 
> > Elsewhere, Howard talked about using paths to access the graph and
> > Treehugger [2] does this by dymanically materialising an XML
document
> > from the RDF abstract graph.
> > 
> > This is getting stuff out of RDF.  The requirement it places on the
> > WG, as I see it, is to produce a format for variable bindings that
is
> > easily digestable by other systems.  That does not automatically
mean
> > an XML format because it is the output of XQuery functions but an
XML
> > format would work (it can be made streamable which RDF isn't).
> > 
> > I have also seem people do queries in JSP taglibs to produce HTML
and
> > also using Velocity to create XHTML from RDF - a standard library to
> > do the variable bindings to Velocity 
> > 
> > > 
> > > This issue has been more or less discussed in the context of
> > > templates, which did not receive strong support at the first f2f
as
> > > a requirement for DAWG.
> > 
> > IIRC the "Templates" discussion was slightly different.  Its about
> > constructing new RDF from information pulled from existing RDF.  See
> > the SeRQL 'construct' [3] operation or "cwm --filter".
> > 
> > >  However I think that NOT having this is going to be a major
> > > stumbling block for adoption of the DAWG recommendation by
> > > application developers and is going to make it very difficult to
> > > get at that sense of loose coupling and content reuse that makes
> > > the web so exciting. 
> > > 
> > > I would like to get a sense from people of how a DAWG spec could
> > > best facilitate this.  Do we need to do this ourselves?  Can we
> > > expose the data model query language in such a way that it can be
> > > usefully applied by XSL Transforms?  Should this be considered out
> > > of scope for the charter? 
> > > 
> > > Thanks,
> > > 
> > > -bryan
> > 
> > [1] http://www.w3.org/2004/Talks/tp-robie/
> > [2] http://rdfweb.org/people/damian/treehugger/
> > [3] http://www.openrdf.org/doc/users/ch05.html#d0e1101
Received on Tuesday, 25 May 2004 09:30:19 GMT

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