Sunday, 22 January 2012

Get Real Data from the Semantic Web - Finding Resources

In my last article, I briefly explained how to get data from a resource using python and SPARQL. This article explains how to find the resource in the first place.
Have you ever been taught how to knit? I you have, then you'll know that you are not usually taught how to cast on (or start off) on your first lesson. That's because it much easier to learn how to knit than it is to cast on.

So it is with the Semantic Web. Once you have a resource URL, it's reasonably easy to extract information linked to that resource, but finding the starting resource is a bit trickier.
So let's just recap how we might get the abstract description for London from DBpedia.

If we know the URL then that's pretty straight forward:
(If you want to follow this tutorial, then you had better copy the file from there.)

RDF types for the DBpedia entry for London
If you don't however, then you'll have to search for it. According to the dbpedia entry, London is many things, including a owl:Thing, there are a lot of Things out there, probably enough to make even the DBpdia  endpoint time out, so let's choose something more restrictive such as yago:Locations but not too restrictive, for example yago:BritishCapitals.

Just to be a smart ass as I finish off, you can get both at the same time by doing this, but don't forget that doing this will stress the SPARQL endpoint more than is probably necessary. Be kind.

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