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Re: RDFQ - RDF Queries in RDF

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Wed, 7 Apr 2004 13:44:06 +0300
Message-Id: <7E52F47D-8880-11D8-80D7-000A95EAFCEA@nokia.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: "ext Eric Prud'hommeaux" <eric@w3.org>


On Apr 07, 2004, at 12:31, ext Eric Prud'hommeaux wrote:
>>
>>    disjunction
>
> Not sure about this. Comments in line below:
>
>> ...
>> 1. Disjunction is supported. Multiple queries in the same input
>> graph are evaluated as disjunct, and multiple target templates
>> in the same query are evaluated as disjunct. Thus
>>
>> {
>>    [a rdfq:Query; ...]
>>    [a rdfq:Query; ...]
>>    [a rdfq:Query; ...]
>> }
>>
>> equates to
>>
>> {
>>    [a rdfq:Query; ...]
>> OR
>>    [a rdfq:Query; ...]
>> OR
>>    [a rdfq:Query; ...]
>> }
>>
>> and
>>
>> {
>>    [a rdfq:Query;
>>     rdfq:target [...];
>>     rdfq:target [...];
>>     rdfq:target [...] ]
>> }
>>
>> equates to
>>
>> {
>>    [a rdfq:Query;
>>     rdfq:target [...];
>> OR
>>     rdfq:target [...];
>> OR
>>     rdfq:target [...] ]
>> }
>
> If I interpret this correctly, this is more a packaging of multiple
> queries into one protocol exchange.

That's one way to look at it. Of course, one could view any form
of boolean expression as a means to package/compress several
queries into one exchange ;-)

> The useful difference being if one
> must ask a combinatorial factor of all the disjunction optoins. For
> reference, see FatAnnotationQuery (EP-4) [1] where the query asks for
> two properties that may be dc1.0 or 1.1. This seems like it would
> require four queries in RDFQ.

I think the issue here is that RDFQ may not provide for quite
as tight a compression as other forms of expression, but one
then has to weigh how often/widely complex boolean expressions
will be needed/used.

>
> Another litmus for disjunction is (if your language supports safe
> negation) whether you can limit the results to not include X or Y. If
> you can't, you must limit it from including X and then do the work
> locally to remove Y.

I consider these to be more "flavors" of disjunction. Just because
RDFQ does not provide disjunction in exactly the same manner or
to the same degree as some other QL, doesn't mean it doesn't
support it.

Patrick


>
> [1]  
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2004JanMar/ 
> 0083.html
>

>

--

Patrick Stickler
Nokia, Finland
patrick.stickler@nokia.com
Received on Wednesday, 7 April 2004 06:45:19 GMT

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