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Re: Reqirement 3.5: subgraph results

From: Dan Connolly <connolly@w3.org>
Date: Tue, 04 May 2004 15:11:47 -0500
To: Rob Shearer <Rob.Shearer@networkinference.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-Id: <1083701507.460.868.camel@dirk>

On Tue, 2004-05-04 at 14:55, Rob Shearer wrote:
> I very strongly object to this requirement. There are a number of
> different reasons.
> 
> First, the suggestion that a query should return a subgraph of the
> original RDF which can then be the subject of the same query (and return
> the exact same thing) is a MAJOR MAJOR constraint on what the query
> language can express. It eliminates any chance of using any information
> other than that encoded in triples to answer the query;

which triples?

>  in fact it
> codifies that any such extension is explicitly illegal. Queries along
> the lines of "must these two nodes be related via either of these two
> properties?" suddenly become impossible to answer when that answer is
> derived via inference, or rules, or some higher-level semantic language.

I don't understand how you come to that conclusion.

Our charter addresses this pretty clearly, no?

"1.8 Derived Graphs

The working group must recognize that RDF graphs are often constructed
by aggregation from multiple sources and through logical inference, and
that sometimes the graphs are never materialized. Such graphs may be
arbitrarily large or infinite."
 -- http://www.w3.org/2003/12/swa/dawg-charter#derivedGraphs


> The answer is simply "yes"; producing an RDF subgraph to justify that
> answer is impossible: the reasons have no canonical RDF representation.

True, for some forms of inference, the "witness" graph is
not a natural byproduct of the computation, if it exists
at all.

[at this point the chair fails to suppress his frustration
that W3C chose to continue to build more layers of semantic
web technology without a corresponding proof syntax. sigh...]


> We should keep in mind that this requirement could completely dictate
> many other aspects of the language.
> 
> Second, just what use case is driving this requirement?

Fair question.

I recall Janne speaking from implementation experience in Amsterdam.
Hmm... the record only captured

 "Janne: Profium - SIR product"
  -- http://www.w3.org/2004/04/22-dawg-irc

Janne, care to elaborate?

>  If you really
> think this requirement is crucial, then feel free to contrive some
> examples. The explicit use case codified in the requirement--that of
> performing exactly the same query against its own result--is obviously
> useless and relevent to no sane user.
> 
> Third, it seems pretty clear that similar functionality to what is
> described here is easily built by client code, and to the exact level of
> detail the user truly desires. When a user performs a query, they know
> what kinds of triples they consider relevent, and provided some kind of
> node-binding result format is provided they can put together the
> explicit triples which model the data they were after. Why are we
> bloating the core query language with a feature that will be used
> seldom, and almost certainly won't offer the flexibility users need when
> they really do use it?
> 
> Finally, the whole notion of returning RDF subgraphs just strikes me as
> philosophically wrong.

To each his own.

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
see you at the WWW2004 in NY 17-22 May?
Received on Tuesday, 4 May 2004 16:12:52 GMT

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