Having trouble with extracting data from from an rdf-file

[Benedikt Tröster]

Hey!

I'm completely new to the rdf-lib and I tried my best to understand the examples. But I couldn't find a good example for my simple task of reading only surnames from an rdf-file (it's portion of the GND, to be exact).

Here is my code:

http://pastebin.com/aGJyS9Vz

Here are the contents of the rdf-file:

http://pastebin.com/x3HVT4vf

This code simply returns nothing...

I don't understand how to achieve what I want... Is there a significant difference when accessing data online and from a file? (I'm a little confused by the BaseURI - What are they used for?)

Greetings and thanks for helping out a newbie :)

[Gunnar Aastrand Grimnes]

Hey Benedikt, 

You have two mistakes, firstly, RDF is triples of subject, predicate, object (s,p,o) - the rdflib resource object lets you tie down the subject part and more easily query the p's and o's to go with that subject. If you wanted to list everything known about a given person, you could have used "resource", but you are actually interested in all (s,o) pairs that are related the surname property. 

The other mistake is the URL for the surname property, you did: 

> gnd.resource('gnd:surname')

but RDFLib doesn't know how to expand the "gnd:" prefix shorthand to the full URL like this. Instead, you define a namespace: 

> GND = Namespace('http://d-nb.info/standards/elementset/gnd#')

and then you can do: 

GND.surname 

to get the a URIRef object representing your property. 

This you can use in a call to graph.subject_objects() and you get your values: 

for person, name in gnd.subject_objects(GND.surname): 

   print person, name

Have fun!

- Gunnar

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[Sergio Fernández]

I've just past you a working example:

http://pastebin.com/vv9TCg8s

some links you should read:

https://rdflib.readthedocs.org/en/latest/
https://rdflib.readthedocs.org/en/latest/intro_to_parsing.html
https://rdflib.readthedocs.org/en/latest/apidocs/rdflib.html#rdflib.graph.Graph.objects

hope this helps

On 25 November 2013 18:27, Benedikt Tröster <ben...@gmail.com> wrote:

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[Benedikt Tröster]

Guys, thanks so much!

It's much clearer to me now!

[Shaozhong Shi]

Hi, Gunnar,

What you are talking about is interesting to me.

I have files which have some triples like the following.

<http://opendatacommunities.org/id/geography/administration/par/E04009840> <http://opendatacommunities.org/def/geography#boundaryAsJSONP> <http://maps.communities.gov.uk/geoserver/ows?service=WFS&version=2.0.0&request=GetFeature&typeName=admingeo:PAR_DEC_2013_EW_WGS84&outputFormat=text/javascript&cql_filter=PAR13CD=%27E04009840%27> .

How can I define something with geography, then specify boundaryAsJSONP, so that I can retrieve the long string definition.

Regards,

David