vaelii.foreign.rdfxml — com.vaelii/vaelii-foreign 0.1.0

Read an RDF/XML document as the same triples vaelii.foreign.turtle yields.

RDF/XML is a third syntax for the graph the other two already carry, so this is a second lexer and not a second reader: it emits {:s :p :o} maps with terms spelled exactly as turtle spells them, and vaelii.foreign.rdf's OWL projection is reached without changing a line of it. Nothing here knows what rdfs:subClassOf means.

Why it has to exist. Turtle is what a person writes and N-Triples is what a dump ships, but RDF/XML is what an OWL ontology is published as — it was the only serialization OWL 1 defined, so the tooling that generates ontologies still emits it. OpenCyc's OWL export, DOLCE, and the OWL product of every OBO Foundry ontology are all RDF/XML. A reader that stopped at Turtle could not open any of them.

The syntax is striped, alternating node and property elements:

<rdf:Description rdf:about="#Dog">            <!-- node:     the subject -->
  <rdfs:subClassOf rdf:resource="#Mammal"/>    <!-- property: one triple  -->
  <rdfs:label xml:lang="en">dog</rdfs:label>
</rdf:Description>

and nearly everything else in the grammar abbreviates that shape. A node element's tag is an rdf:type triple unless it is rdf:Description; an attribute that is not syntax is a triple with a literal object; rdf:parseType switches the content between three readings; rdf:li counts. The awkward part of RDF/XML is not the striping but how many ways it offers to write one triple, and this reader's job is that every one of them lands as the same data.

Parsed with the JDK's StAX, pulled one top-level node element at a time, so a 252 MB ontology streams rather than building a DOM. DTD support is on because RDF/XML routinely declares internal entities for its namespaces (<!ENTITY owl "http://…">, then &owl;Class) and a parser rejecting those could not read the files it exists for; external entities are off, which is what keeps that safe.

What is approximated. rdf:parseType="Literal" should hold the exclusive XML canonicalization of its content. This writes a faithful but not canonical serialization — attribute order and namespace declarations may differ from C14N — so an XMLLiteral compares equal to itself and not necessarily to another parser's. No ontology reasons over one, and vaelii.foreign.rdf keeps it as a string.

triples clj

(triples rdr)

(triples rdr opts)

Every triple rdr holds, as a lazy seq of {:s :p :o} maps — the same shape vaelii.foreign.turtle/triples returns, so a caller need not know which syntax it got.

One top-level node element is parsed per pull, which is what keeps a large ontology streaming: the queue holds one class's description, not the document.

opts may carry :base, for a document whose own xml:base is absent and whose relative IRIs are meant to resolve against where it was fetched from.

with-triples clj

(with-triples path f)

(with-triples path f opts)

Open the RDF/XML file at path, call (f triples) on a lazy seq of its triples, and close the file after. .gz is decompressed on the way through — the OpenCyc OWL export ships that way and is a tenth the size for it.