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Definition of constraint?

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Thu, 16 Dec 2004 13:49:21 +0000
Message-ID: <41C19261.3020002@hp.com>
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>

Pat,

I'm struggling to incoporate your text for constraints into the document.

Specifically, your text uses an example to explain it so I wondered what you had 
in mind as the definition of a constraint?  Does "boolean-valued expressions on 
datatype values" suffice?

	Andy

For reference the text in http://www.ihmc.us/users/phayes/SPARQLdefs.html is
"""
1. Constraints. A pattern may contain a constraint, such as v==val, where val is 
an indication of a datatype value. In this case the answer must bind v to a 
typed literal whose datatype value is equal to val. Other constraints are 
defined in @@@; they all amount to boolean-valued expressions on datatype 
values. Answer substitutions are required to bind variables occurring in 
constraints to typed literals such that the constraint is true when applied to 
the value of the typed literal. In this way, patterns may constrain literals to 
have particular values rather than having particular syntactic forms. Note that 
a constraint can be considered to be a triple with a special predicate. An 
answer substitution
"""
Received on Thursday, 16 December 2004 13:49:31 GMT

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