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Re: Technical issues impacting government use of linked data

From: Thomas Bandholtz <thomas.bandholtz@innoq.com>
Date: Sun, 14 Mar 2010 15:50:07 +0100
Message-ID: <4B9CF79F.1070003@innoq.com>
To: Cory Casanave <cory-c@modeldriven.com>
CC: public-egov-ig@w3.org
For metadata about Linked Data we have the "Vocabulary of Interlinked
Datasets (voiD)", see http://rdfs.org/ns/void-guide. In voiD you can
describe the SPARQL endpoint (issue 2) of a dataset and give links to
interlinked (associated) datasets (at least this about issue 4), and
there are some hooks for linking provenance (issue 3) statements.

voiD considers "Discovery via links in the dataset's documents" (issue
1) using back-links as dcterms:isPartOf from one "document" (i.e. data
item) to the dataset:

    <http://dbpedia.org/data/Berlin> dcterms:isPartOf :DBpedia .

    :DBpedia a void:Dataset ;
             dcterms:title "DBPedia" ;
             dcterms:description "RDF data extracted from Wikipedia" ;
             foaf:homepage <http://dbpedia.org/> ;
             void:exampleResource <http://dbpedia.org/resource/Berlin> ;

I would prefer rdfs:isDefinedBy instead which "is used to indicate a
resource defining the subject resource. This property may be used to
indicate an RDF vocabulary in which a resource is described."
http://www.w3.org/TR/rdf-schema/#ch_isdefinedby

In SKOS we have skos:inScheme with a similar meaning.

This gives patterns for issue 1-3 at least.

Issue 4 is something in ongoing discussion about "RDF federation", or
"SPARQL Federation", which requires a solution from the server side.
Sandro has worked on this.

Anyway, starting with one dataset's voiD, you can lookup the SPARQL
endpoints of the interlinked datasets in their respective voiD metadata
and query all those. However, each dataset may have a different RDF
schema, so you might be restricted to searching the rdfs:label
assertions as the only common query ;-)
This is not so easy.
But how would you solve this with relational databases and Web Service
interfaces? Absolutely no chance!

Olaf Hartig and Juan Sequeda are currently working on "SQUIN - Query the
Web of Linked Data"
"This service executes queries over the whole Web of Linked Data and,
hence, enables applications to access the whole Web as if it is a single
giant database."
http://squin.sourceforge.net/

Have a nice weekend!
Thomas

Cory Casanave schrieb:
> On the demo call today we discussed a couple of technical issues that
> impact but are not specific to government.  These are:
> 
> 1)       That given a data URI, there is no standard way to
> programmatically access the metadata about the resource.
> 
> 2)       That given a data URI there is no standard programmatic way to
> access a SPARQL query point for that resource and/or for associated
> resources.
> 
> 3)       That the metadata accessed should have standard links for
> provenance – even very simple provenance that does not require research
> 
> 4)       How do we contextualize a query such that all data resources of
> interest within a certain context are included in a query, without the
> user having to know all the details of the data sets involved?
> 
>  
> 
> All of the above could be accomplished with URI conventions and
> supporting ontologies.   My question is: What are the existing or
> proposed conventions and ontologies to satisfy these requirements?
>  Should the eGov group provide or reference such conventions for use by
> the government and/or within our government demos?
> 
>  
> 
> Regards,
> 
> Cory Casanave
> 

-- 
Thomas Bandholtz, thomas.bandholtz@innoq.com, http://www.innoq.com
innoQ Deutschland GmbH, Halskestr. 17, D-40880 Ratingen, Germany
Phone: +49 228 9288490 Mobile: +49 178 4049387 Fax: +49 228 9288491
Received on Sunday, 14 March 2010 14:50:39 GMT

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