Thursday, December 04, 2008

Getting Groovy with JRDF

In an effort to speed up and improve the test coverage in JRDF I've started writing some of the tests in Groovy. It's been a good experience so far - so much so that I'm probably not going back to writing tests in Java in the future.

One of the things I wanted to try was a RdfBuilder, this is similar to Groovy's NodeBuilder.

There are a couple of things that make it a bit tricky. When parsing or debugging builders I haven't yet found a way to find the methods/properties available even using MetaClass. And of course, when the magic goes wrong it's a bit harder to debug Groovy versus java.

It certainly smartens up the creation of triples, for example (bits from the NTriples test case):
def rdf = new RdfBuilder(graph)
rdf.with {
namespace("eg", "http://example.org/")
namespace("rdfs", "http://www.w3.org/2000/01/rdf-schema#")
"eg:resource1" "eg:property":"eg:resource2"
"_:anon" "eg:property":"eg:resource2"
"eg:resource1" "eg:property":"_:anon"
(3..6).each {
"eg:resource$it" "eg:property":"eg:resource2"
}
"eg:resource7" "eg:property":'"simple literal"'
"eg:resource17" ("eg:property":['"\\u20AC"',
'"\\uD800\\uDC00"', '"\\uD84C\\uDFB4"', '"\\uDBFF\\uDFFF"'])
"eg:resource24" "eg:property":'"<a></a>"^^rdfs:XMLLiteral'
"eg:resource31" "eg:property": '"chat"@en'
}
The first two lines defines the two namespaces used. The third line shows the general use of RDF and Groovy. It works out well, an RDF predicate and object maps to an attribute and value in Groovy. The next two lines show how you refer to the same blank node across two statements. And the following lines show using ranges and creating different types of literals. The third last line creates 4 triples with the same subject and predicate but with different objects.

Using the builder results in a file that's smaller than the test case file. You could remove some duplication by creating a method that takes in a number and the object and generates "eg:resource$number" "eg:property" "$object" but doing that may actually make it harder to read.

If you stick to only using URIs you can do things like:
rdf.with {
urn.foo6 {
urn.bar {
urn.baz1
urn.baz2
}
}
}
Which produces two triples: "urn:foo6, urn:bar, urn:baz1" and "urn:foo6, urn:bar, urn:baz2".

I expect that JRDF will only be more Groovy friendly in the future.
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