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Comments on SPARQL Query Language for RDF (21 July 2005 version)

From: <Art.Barstow@nokia.com>
Date: Thu, 1 Sep 2005 13:12:32 -0400
Message-ID: <EF72EBD03EAED74C91670141D409ACBB942D1D@bsebe101.NOE.Nokia.com>
To: <public-rdf-dawg-comments@w3.org>
Cc: <Ora.Lassila@nokia.com>

Regarding the 2005-07-21 version of the SPARQL Query 
Language for RDF document, we have the following comments:

1) This document does not discuss in any way the 
*semantics* of the query language. We would like to see 
a more formal definition of queries (and their results) 
in terms of RDF semantics (right now, the query language
seems to treat RDF graphs as merely data structures from 
which something can be extracted). Why would SPARQL now 
ignore RDF's model theory when one was created through 
a sizeable effort?

2) Given that RDF representations -- effectively -- are 
graphs, why would the W3C present a query language based 
on relational algebra? It is well known [1] that relational 
algebra is insufficient for querying graphs (generally, 
data structures that exhibit repetitive or recursive patterns). 
In order to query, say, hierarchies of arbitrary depth, the 
query language should have some means of expressing 
a transitive closure.

3) It does not seem possible to extend SPARQL to be 
used with OWL (primarily, perhaps, because of comment
#1 above).


Art Barstow

[1] Aho, A.V., Ullman, J.D.: Universality of data retrieval 
languages. In: POPL 79: Proceedings of the 6th ACM SIGACT-SIGPLAN 
symposium on Principles of programming languages, ACM Press (1979) 
Received on Thursday, 1 September 2005 17:12:43 UTC

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