xml schema for skos

[Frederic Hessman]

I hate to mention it (well, not really), but I long ago said that part  
of the IVOA vocabulary proposal should have been suggestions for the  
exact format of RDF/XML so that a formal IVOA RDF/XML schema could  
have been reality, making the practical parsing of vocabularies much  
simpler (for all of the Roy William's and Alasdair Allen's of the  
world that don't want to add Turtle, n-triple, OWL, and arbitrarily  
complex RDF parsers to their list of needed tools).

Rick

> > I am trying to incorporate SKOS vocabularies in SimDB.
> > For a proto-type implementation that uses JAXB for XML
> > (un)marshalling I
> > could use an xml schema describing the XML syntax of SKOS. Does this
> > exist,
> > can someone point me to it?
>
> There isn't such a schema, I'm afraid.
>
> SKOS is an RDF vocabulary, so processing a SKOS vocabulary means  
> processing an RDF graph (albeit one with a _very_ simple structure).  
> RDF has three well-known serialisations: RDF/XML, Turtle (also  
> called Notation3 or n3) and n-triples.
>
> What you're (presumably) looking at is RDF/XML, which is a  
> serialisation of an RDF graph as XML. It's syntactically well-formed  
> XML, but not described by a schema, but instead by a set of rules  
> described in [1]. Though any RDF/XML file will be deserialised to  
> give equivalent RDF, a given RDF graph could be serialised into  
> multiple rather different-looking XML files.
>
> The SKOS files that are part of the Vocabularies document are pretty  
> regular, but could in principle be written in different ways. Also,  
> other SKOS vocabularies could use write their RDF/XML taking  
> advantage of the freedoms that [1] provides.
>
> I'm aware that there are a couple of stylesheets which can grok  
> reasonably general RDF/XML, and there are a couple of proposals for  
> alternative XML syntaxes for RDF, none of which has gained much  
> traction. Fundamentally, if you're going to process RDF, it's best  
> to process it as RDF. There are assorted tools which can parse, and  
> translate between, RDF syntaxes: librdf.org is a well-known one with  
> bindings to multiple languages. Translating the vocabulary into n-  
> triples, which is _very_ easy to parse, may be a useful step.
>
> This is admittedly more hassle than you were anticipating! During  
> the development of the Vocabularies document, there was some  
> discussion (initiated by Rick) about specifying an XML-friendly  
> profile of RDF/ XML. The problem with that is that specifying some  
> sort of RDF/XML- lite would involve quite a lot of work: beside the  
> specification and validation work rquired, this would also preclude  
> using generic RDF tools to work with the vocabularies, since these  
> wouldn't, obviously, be able to generate the RDF/XML profile.
>
> Having said that, it occurs to me that there may be a way to specify  
> a non-mandatory XML serialisation format for vocabularies, in a  
> fairly principled way, and without massive effort. How much hassle  
> does the above RDF-parsing sound?
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