W3C home > Mailing lists > Public > public-rdf-dawg@w3.org > October to December 2004

Re: tests and inference? (and UNSAID)

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 21 Dec 2004 19:24:51 -0800
Message-Id: <p06001f03bdee97dcccac@[192.168.1.4]>
To: "Seaborne, Andy" <andy.seaborne@hp.com>
Cc: Steve Harris <S.W.Harris@ecs.soton.ac.uk>, RDF Data Access Working Group <public-rdf-dawg@w3.org>

>Steve Harris wrote:
>>On Sun, Dec 19, 2004 at 09:01:05 -0600, Dan Connolly wrote:
>>
>>>>My engine has no way to turn off inference (though it wouldn't be hard to
>>>>add globaly), but I'd like it if that was possible on a per-statement way
>>>>via the query language.
>>>
>>>I'm not sure what you mean; it makes more sense, to me, to specify what
>>>you're querying against in the FROM clause. If we wanted explicit
>>>support for "turning RDFS inferencing off" in SPARQL, I'd expect it
>>>to look something like:
>>>
>>>	SELECT ?C FROM rdfs(<mydata.rdf>) WHERE ( :x rdf:type ?C).
>>>vs.
>>>	SELECT ?C FROM <mydata.rdf> WHERE ( :x rdf:type ?C).
>>
>>
>>[turning off wasn't really what I was thinking of, but I cant think of a
>>better term, ignoring maybe]
>>
>>OK, well I would expect it to look more like
>>
>>	SELECT ?C WHERE GROUND (:x rdf:type ?C)
>>
>>I dont really like FROM as it doesn't make much sense in server-like
>>systems where all the graphs are preloaded (for performance or security
>>reasons), or systems that are reflecting underlying data in another format
>>and translating queries on the fly.
>
>FROM could make sense - the server offers a numer of graphs and the 
>URI in teh FROM must choose one of them.  If it names some graph the 
>server is not publishing, then the query generates an error.  FROM 
>isn't a requirements to load any graph (I worry about the security 
>issues of that).  A server may require that there is only one URI in 
>the FROM clause - i.e. no arbitrary RDF merge of graphs.  It is just 
>a request for something that the server does not offer.

Agreed. I think we should allow a server to refuse to answer a query 
if it names FROM a graph that the server cannot (prefers not to) 
access, and we should allow the query to provide a variable in the 
FROM position which gets bound to the name of the source as part of 
the answer, so that a query can say, in effect: answer this from any 
source you choose, but tell me what the source was. Query-answering 
servers should be required to provide a binding to any such variable, 
even if it is a 'trivial' one which simply identifies the server 
itself (which means, roughly: I am the source, and that's all you are 
going to get out of me on that topic.)

BTW, there should not be a requirement on a server that the same 
query from the same source will produce the same result each time. 
But it might be useful to enable a server which does undertake to be 
stable in this way, to advertise the fact that it is stable.

Pat

>(This use of FROM is one mode for Joseki I'm considering)
>
>	Andy
>
>>
>>- Steve


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Received on Wednesday, 22 December 2004 03:25:46 GMT

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