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Re: bnodes as answer bindings

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Mon, 7 Aug 2006 17:33:02 +0100
Message-Id: <CC5E03DD-8CF1-45D5-AA17-24CF1B5C13CE@cs.man.ac.uk>
To: Pat Hayes <phayes@ihmc.us>, RDF Data Access Working Group <public-rdf-dawg@w3.org>

Slight emendation:

On Aug 7, 2006, at 5:22 PM, Bijan Parsia wrote:
[snip]

> """The answer set of a query is the largest set of query answers  
> that are entailed by the answer KB such that no answer in the set  
> is entailed by any other answer in the set."""
>
> Non-redundancy.
[snip]

DQL distinguishes between the answer set and the response set:

"""Response Set
While there are no global requirements on a response set other than  
that all its members are correct answers, it is recommended that  
servers ensure that answer bundles do not contain duplicate or  
redundant answers, i.e., answers which are subsumed by other  
answers.  One answer subsumes another if its bindings are a superset  
of the bindings in the other answer.  Servers that are able to  
guarantee that their response sets contain no duplicate answers can  
be called non-repeating.  Servers that are able to guarantee that  
their response sets contain no duplicate or redundant answers can be  
called terse.  Servers that are able to guarantee that their response  
sets will be correctly terminated with 'none' can be called complete."""

OWLQL (<http://ksl-web.stanford.edu/KSL_Abstracts/KSL-03-14.html>) as  
a more elaborate discussion.

I think I prefer the way that SPARQL does it, if DISTINCT gets fixed.  
I certainly don't want to have the granularity of redundancy placed  
at the server level. If I can't compute a non-redundant answer  
because I've run out of resources, I should timeout/fault with out of  
memory, whatever. If I have an imcomplete minimizer, I should be able  
to verify that that my answer set is minimal, or fault. The  
difficulties of streaming answers isn't really addressed in SPARQL,  
but I'm not sure that they are quite the same for SPARQL.

"""Guaranteeing terseness is a quite harsh requirement on a server  
that is incrementally deriving answers and returning bundles of  
answers as they are produced.  The difficulty is that if such a  
server derives and returns an answer A1 with an unbound may-bind  
variable (i.e., A1 does not provide a binding for that variable),  
then it cannot later return any answer A2 that it derives containing  
the same bindings as those in A1 with the addition of a binding for  
the unbound may-bind variable because A1 would subsume any such A2.   
Similarly, if such a server derives and returns an answer A1 with a  
binding B for a variable V that occurs in the query only as a value  
in a minCardinality (maxCardinality) restriction in the query  
pattern, then it cannot later return any answer A2 that it derives  
containing the same bindings as those in A1 with the addition of a  
binding for V that is less than (greater than) B because A1 would  
subsume any such A2. """

Don't have anything to say about this, really, right now.

Cheers,

Bijan.
Received on Monday, 7 August 2006 16:32:30 GMT

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