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No way to specify an RDF dataset of all the known named graphs

From: Chimezie Ogbuji <ogbujic@ccf.org>
Date: Wed, 04 Apr 2007 17:05:38 -0400
To: public-rdf-dawg-comments@w3.org
Message-ID: <1175720738.16940.0.camel@otherland>

This was discussed in #swig
(http://chatlogs.planetrdf.com/swig/2007-04-03.html#T20-38-01)

SPARQL currently does not provide an unambiguous way to specify a
dataset which corresponds to all the known named graphs.  The only way
this can be done is to leave out FROM <..> and FROM NAMED <..>
directives in the prolog (and from the protocol, for SPARQL services).
The corresponding dataset in this case depends on the host application -
not very consistent. The only other alternative is to explicitly
enumerate the known universe in the prolog:

FROM NAMED G1
FROM NAMED G2
...
FROM NAMED GN

This is not practical for a dynamic dataset.

There is plenty of value in querying against the known universe
consistently especially for applications which make use of a dataset as
a named graph partition that can grow indefinitely.  Consider XPath
2.0 / XQuery 1.0 which supports querying a collection of XML documents
without having to explicitly enumerate all the XML documents in the
collection.

This is a very useful 'database-wide' query pattern which is well
supported in document-management languages but not supported in SPARQL
without assuming the implementation will consistently supply the dataset
corresponding to all the known named graphs in persistence in the
absence of any dataset directives in the prolog or at the protocol
level.

Other than OWA or CWA issues, I don't see why an explicit syntax for
binding to such a dataset is not supported by SPARQL to provide a
consistent way for applications to dispatch these kinds of queries.
Such a syntax was suggested in the above conversation:

FROM NAMED *

[1] http://www.w3.org/TR/xquery-semantics/#sec_fn_doc_collection

-- 
Chimezie Ogbuji
Lead Systems Analyst
Thoracic and Cardiovascular Surgery
Cleveland Clinic Foundation
9500 Euclid Avenue/ W26
Cleveland, Ohio 44195
Office: (216)444-8593
ogbujic@ccf.org






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Received on Wednesday, 4 April 2007 21:06:16 GMT

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