Matthieu Riou wrote:
> I think I really suck at RDF (I'm more a BPEL kind of guy) but here is my
> try at using it for the licenses descriptors format:
>
> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"; xmlns:dis="
> http://labs.apache.org/discordia";>
> <rdf:Description rdf:about="mvn://org.apache.velocity/velocity/1.4">
>
>
> </doap:Project>
> <dis:has_license rdf:about="
> http://www.apache.org/licenses/LICENSE-2.0.txt"/>
> </rdf:Description>
> </rdf:RDF>
>
> To the RDF experts, feel free to criticize, propose corrections or insult me
> :)
The above is invalid RDF.
Everything in RDF needs to be translated into triples and the above
cannot be (you have rdf:Description and doap:Project nested without a
relationship in between). Here is what you want to say
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#";
xmlns:doap="http://usefulinc.com/ns/doap#";
xmlns:dis="http://labs.apache.org/discordia";>
<doap:Project rdf:about="mvn://org.apache.velocity/velocity/1.4">
<doap:name>Apache Velocity<doap:name>
<dis:has_license
rdf:resource="http://www.apache.org/licenses/LICENSE-2.0.txt"/>
</doap:Project>
</rdf:RDF>
A few things to note:
1) rdf:Description is just a placeholder for when you don't know what
"type" of object you're using, so you can avoid using it alltogether if
you already know that doap:Project is the 'rdf:type' of
'mvn://org.apache.velocity/velocity/1.4'
[I know, this is confusing as hell, RDF/XML is a pain]
2) you use "rdf:about" when you want to use the URL as 'subject' but
you use 'rdf:resource' when you want to use the URL as 'object'
[yes, another one of those things]
3) I strongly advice *NOT* to use 'http://labs.apache.org/discordia' as
the namespace for this ontology. Something like
"http://apache.org/ns/2007/discordia#"; is much less likely to be able to
point to an RDF description of the ontology for machine discovery while
'http://labs.apache.org/discordia' might change (the lab might move) or
might simply have no way to differentiate between the ontology and the
home page of the lab itself.
4) the use of "mvn:" URIs is a problem according to TimBL's notion of
'linked data'. He suggests the use of HTTP URIs so that machines could
use HTTP to self-discover more information about that entity. A possible
URI scheme that is both plausible and usefule is
http://apache.org/ns/org.apache.velocity/velocity/1.4
- o -
BTW, I've learned to stay away from RDF/XML entirely and write stuff in
RDF/N3 instead, which is both more readable, more compact and it's way
harder to write invalid RDF by hand.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix doap: <http://usefulinc.com/ns/doap#> .
@prefix dis: <http://apache.org/ns/2007/discordia#> .
<http://apache.org/ns/org.apache.velocity/velocity/1.4>
rdf:type doap:Project ;
doap:name "Apache Velocity" ;
dis:has_license <http://www.apache.org/licenses/LICENSE-2.0.txt> .
HTH
--
Stefano.
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