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Re: paper on RDF querying relevant to DAWG (and to current discussions)

From: Sergio Tessaris <tessaris@inf.unibz.it>
Date: Wed, 29 Mar 2006 14:34:00 +0200
Message-Id: <18E40BA2-D4DA-470B-8A92-73615187D31F@inf.unibz.it>
Cc: public-rdf-dawg-comments@w3.org, public-rdf-dawg@w3.org
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>


On 29 Mar 2006, at 14:07, Peter F. Patel-Schneider wrote:

>
> I am a bit confused as to just what is being proposed here.
>
> I would have have been satisfied with a simple acknowledgment in  
> the SPARQL
> documents that the work I mentioned is related to SPARQL.  I don't  
> see any
> reference to such an acknowledgment.

Peter, I'm not sure whether the SPARQL document is the right place  
for a survey/comparison of different approaches to the problem of  
querying RDF(S) documents. If this is the case I think that there are  
other relevant references which didn't find their way into the document.

The technical contents of Mendelzon's work have been brought to the  
attention of the WG. Moreover, changes to the initial SPARQL draft  
have been influenced by this work. It could be worth pointing it out  
by means of references in the WG web pages.

I reckon that a specific document on the relation of SPARQL with  
other query languages would be a useful contribution to the Semantic  
Web community; but I see it as a complementary document to the  
current SPARQL document.

Cheers,
--sergio

>
> However, in the end, this is not a technical isues, and thus I am  
> not going
> to make a fuss over it, particularly as I am making a fuss over  
> technical
> issues.  If the DAWG feels that it does not need to reference prior
> closely-related work, I'm not in a position to prevent it from so  
> doing.
>
> What makes the lack of reference to the work by Mendelzon even more  
> jarring
> to me is the inclusion of at least one reference (CBD) that has  
> less to do
> with the design of SPARQL than Mendelzon's work does.  There is even a
> reference in the reference list (VCARD) that is not pointed to from  
> the
> body of the document.
>
> peter
>
> From: Sergio Tessaris <tessaris@inf.unibz.it>
> Subject: [OK?] paper on RDF querying relevant to DAWG (and to  
> current discussions)
> Date: Wed, 29 Mar 2006 09:18:46 +0200
>
>> ---
>> Please respond indicating whether you are or are not satisfied with
>> this response. If you are, you can help our issue tracking system by
>> prefixing the subject of your response with [CLOSED] (where this
>> subject has [OK?]).
>> ---
>>
>> The mentioned papers indeed present a coherent and well defined
>> framework for the problem of querying RDF graphs. However, the query
>> language proposed is somewhat restricted and doesn't fulfil the
>> requirements for SPARQL (see [UCNR]).
>>
>> Moreover, in its basic definitions is not far away from the current
>> version of the SPARQL document. In fact, a tableau as defined in the
>> paper can be seen as a CONSTRUCT query containing a single graph
>> pattern, where the head and the body of the tableau are the template
>> and the graph pattern respectively. The semantic definitions in
>> Section 4.2 of the paper are substantially equivalent to those of the
>> latest SPARQL document. In particular, the definition of pre-answer
>> correspond to the SPARQL answer set (provided that valuations are
>> considered instead of graphs).
>>
>> Note that the notion of answers to a query is defined in terms of
>> subgraph homomorphism; so, although it works well with RDF(S) has
>> problems in scaling up with more expressive ontology languages (see
>> owlDisjunction  issue at http://www.w3.org/2001/sw/DataAccess/
>> issues#owlDisjunction).
>>
>> In the paper, two different semantics are considered for the result
>> of a query as the combination of the graphs in the so called pre-
>> answer, namely the union or the (RDF) merge. In SPARQL, the CONSTRUCT
>> operator adopts the merge semantics.
>>
>> Constraints, as introduced in the paper correspond to the FILTER
>> operator in SPARQL.
>>
>> The paper introduces the idea of premises for a query, which can be
>> easily handled by SPARQL by means of the ability of querying multiple
>> graphs.
>>
>>
>> Regards,
>> --sergio
>>
>> [UCNR] RDF Data Access Use Cases and Requirements , K. Clark, Editor,
>> W3C Working Draft. Latest version available at http://www.w3.org/TR/
>> rdf-dawg-uc/ .
>>
>> On Sunday 18 September 2005 17:02, Peter F. Patel-Schneider wrote:
>>> Hi:
>>>
>>> A couple of days ago I came across the following paper:
>>>
>>> 	Foundations of Semantic Web Databases.
>>> 	Claudio Gutierrez, Carlos Hurtado - Universidad de Chile;
>>> 	Alberto Mendelzon - University of Toronto.
>>> 	PODS 2004, pp. 95 - 106.
>>>
>>> The paper refers to an earlier paper, "Formal aspects of querying  
>>> RDF
>>> databases", "for the case with no rdfs vocabulary" that was
>>> presented at
>>> the First International Workshop on Semantic Web and Databases co-
>>> located
>>> with VLDB held at Berlin, Germany, September 7-8, 2003.
>>>
>>> These papers have a very good set of definitions for querying RDF.
>>> Although the second, more developed, paper concentrates on the case
>>> of RDFS
>>> its solutions appear to be directly relevant to the Data Access  
>>> Query
>>> Working Group.
>>>
>>>
>>> Peter F. Patel-Schneider
>>> Bell Labs Research
>>
>> -- 
>> --------------------------------------------------------------------- 
>> --
>> Sergio Tessaris, Assistant Professor        Faculty of Computer  
>> Science
>> e-mail: tessaris@inf.unibz.it          Free University of Bozen- 
>> Bolzano
>> http://www.inf.unibz.it/~tessaris                   Piazza  
>> Domenicani 3
>> tel: +39 0471 016 125 (fax 009)                    39100 Bolzano,  
>> Italy
>

Sergio Tessaris, Assistant Professor        Faculty of Computer Science
e-mail: tessaris@inf.unibz.it          Free University of Bozen-Bolzano
http://www.inf.unibz.it/~tessaris                   Piazza Domenicani 3
tel: +39 0471 016 125 (fax 009)                    39100 Bolzano, Italy
Received on Wednesday, 29 March 2006 12:34:23 GMT

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