Unfortunately, we're not there yet. I've been trying to make sense of TreeBASE II RDF, and frankly, it's a mess. Here are some of the problems:
TreeBASE URIs aren't linked data compliant
The canonical URI for a study (e.g., http://purl.org/phylo/treebase/phylows/study/TB2:S10423) doesn't conform to the linked data approach. In fact, the URI crashes the linked data validator, so I tried another test.
curl --include
--header "Accept: application/rdf+xml"
http://purl.org/phylo/treebase/phylows/study/TB2:S10423
To be a valid linked data resource this request should return a 303 HTTP status code. Instead we get a 302 and some HTML. Linked data clients won't be able to extract information from this URI.
SKOS matching
There are some odd things going on in the RDF. It contains statements of the form:
<rdf:Description rdf:ID="otu1789319">
<skos:closeMatch rdf:resource="http://purl.uniprot.org/taxonomy/76066.rdf">
</rdf:Description>
(I've tidied this up a little from the original, rather verbose RDF). This asserts that the TreeBASE OTU otu1789319 corresponds to the NCBI taxon with the taxonomy id 76066 (represented by the Uniprot URI). Except, it doesn't really. As far as I understand it, SKOS is about matching concepts, not documents. The URI http://purl.uniprot.org/taxonomy/76066.rdf is a document URI (specifically, a RDF document), the URI http://purl.uniprot.org/taxonomy/76066 is the taxon. The match should really be to http://purl.uniprot.org/taxonomy/76066. Then I've come across statements that match TreeBASE OTUs to http://purl.uniprot.org/taxonomy/0.rdf. This URI doesn't exist (we get a 404). This seems an odd way to say that we don't have a match -- if we don't have a match, don't include it in the RDF.
Local URIs for trees don't work
The RDF is full of local URIs such as http://purl.org/phylo/treebase/phylows/#tree1790755, which don't resolve. In fact they generate a rather spectacular Tomcat exception. I don't understand why we need local URIs. Everything in TreeBASE should have a global URI. Then we can avoid unnecessary statements such as:
http://purl.org/phylo/treebase/phylows/#tree1790755 owl:sameAs http://purl.org/phylo/treebase/phylows/tree/TB2:Tr7899
which links a local resource to a global one http://purl.org/phylo/treebase/phylows/tree/TB2:Tr7899. Incidentally, this URI doesn't resolve, despite claims that this bug has been fixed.
No links between tree and study
But the show stopper for me is that there is no link between a study and a tree! There is no triple in the RDF specifying any relationship between these two entities. To me this is just about the most important thing I need. I want to be able to query TreeBASE RDF using a study identifier (either from TreeBASE itself, or from an external identifier such as a DOI or a PubMed number). As it stands the TreeBASE II RDF is almost useless. I can't get it via a linked data client, it's full of URIs that don't resolve, and it lacks key triples that would glue things together.
RDF != XML
I can't help thinking that the RDF output hasn't been designed with end use in mind. I know from my own experience that it's not until you try to do something with the RDF that you realise how poor some design decisions may have been.
It's not enough to pump out RDF and hope for the best. RDF is not XML, which is just a verbose format for moving data around. RDF brings with it all sorts of expectations about how clients will resolve it, how they will interpret URIs, and the kinds of queries that will be performed. We are achingly close to being able to tie everything together, but not with RDF TreeBASE II is currently making available.
