Re: Dynamically Merging Multiple Named Graphs?

Lee Feigenbaum Tue, 25 Aug 2009 06:13:24 -0700

Hi Jamey,

I don't think there's any way to do what you're looking for in SPARQL.

In your particular example, you could query with the full contents ofthe store merged as the query's default graph, but I realize thatdoesn't work in the general case.


Sorry I don't have a more helpful answer here!

Lee

Wood, Jamey wrote:

I’m trying to find a good way to contextualize RDF statements (so that
statements could be bound to a certain time period, licensing terms, etc).
Named graphs seem to handle this pretty well.  But I can’t find a good way
to query across all named graphs which match some criteria.

I’ll try to illustrate the issue I’m facing via an example.  Suppose we have
the following graphs:

  @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
  @prefix xsd: <http://www.w3.org/2001/XMLSchema#>
  @prefix ex: <http://example.org/vocabulary#> .
  @prefix : <http://example.org/exampleDocument#>

  # default graph
  {
    <urn:g1> ex:startDate "1809-02-12T00:00:00Z"^^xsd:dateTime .
    <urn:g1> ex:endDate "1865-04-15T00:00:00Z"^^xsd:dateTime .
    <urn:g2> ex:startDate "1839-02-12T00:00:00Z"^^xsd:dateTime .
    <urn:g2> ex:endDate "1840-02-12T00:00:00Z"^^xsd:dateTime .
    <urn:g3> ex:startDate "1840-02-12T00:00:00Z"^^xsd:dateTime .
    <urn:g3> ex:endDate "1841-02-12T00:00:00Z"^^xsd:dateTime .
  }

  <urn:g1> {
    :Abraham_Lincoln rdf:type ex:LivingPerson .
  }

  <urn:g2> {
    :Abraham_Lincoln ex:age "30"^^http://www.w3.org/2001/XMLSchema#integer ..
  }

  <urn:g3> {
    :Abraham_Lincoln ex:age "31"^^http://www.w3.org/2001/XMLSchema#integer ..
  }

(So the default graph just contains “context information” and the “real” data 
is in the named graphs.)

Now suppose that I want to write a query to get the age of all living persons 
on a particular day.
In other words, I'd like to do something kind of like this:

  PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
  PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
  PREFIX ex: <http://example.org/vocabulary#>
  PREFIX : <http://example.org/exampleDocument#>

  SELECT ?person $age
  WHERE {
    GRAPH ?g {
      ?person rdf:type ex:LivingPerson .
      ?person ex:age ?age .
    }
    ?g ex:startDate ?ctx_startDate .
    ?g ex:endDate ?ctx_endDate .
    FILTER (("1840-04-01T00:00:00Z"^^xsd:dateTime >= xsd:dateTime(?ctx_startDate)) 
&&
            ("1840-04-01T00:00:00Z"^^xsd:dateTime <= 
xsd:dateTime(?ctx_endDate)))
  }

....except that won't work, since the "rdf:type ex:LivingPerson" and "ex:age 
31" assertions
live in two different graphs (even though each of those graphs represents a 
context which
does contain April 1, 1840).

Is there some way to make this work?  Essentially, I think I'm looking for a 
way to
have a query construct a dynamic merge of named graphs (without having to know 
the names
of those graphs up-front).

I’ve looked at the proposal for Composite Datasets
(http://www.w3.org/2009/sparql/wiki/Feature:CompositeDatasets), and it sounds 
somewhat
like what I’m seeking.  But even with it, it sounds like I’d need to explicitly 
specify
the graphs which I wanted to merge (instead of being able to just specify 
criteria about
them, and letting the system find them).  Correct?

Also, I should note that I’m fairly new to semantic web technologies.  So my 
apologies
In advance if I’ve botched any of the above syntax or am just approaching this 
in a screwy
way.

Thanks,
Jamey

Re: Dynamically Merging Multiple Named Graphs?

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