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Successive Bindings, cascaded queries in Algae2

From: Eric Prud'hommeaux <eric@w3.org>
Date: Tue, 18 Jan 2005 23:28:46 -0500
To: public-rdf-dawg@w3.org
Message-ID: <20050119042846.GD13055@w3.org>
In his issues WBS response, Kendall mentioned Algae's approach to
cascaded queries. I propose SPARQL adopt the same approach, which is:

The Algae2 results set [1] holds the know bindings at any point. It is
defined as starting as a single result with no bindings (what we were
calling "true" in DAWG). asks [2] are made of decls [3] which have the
following semantics:

A single decl specifies that each result in the result set be replaced by (zero or more) results obtained from the following two steps:
1 Substitute the variables from that result for the variables in the decl and search for the resulting triple in the (current) database.
2 Evaluate the constraints on the triples obtained from step 1.

Thus, successive asks are constrained by the values bound in the
result set by earlier asks.  This, and the ability to target queries,
was used in the pharma federation example [4].

The SPARQL spec goes to some effort to make sure that the clauses in a
query can be executed in any order. This is compatible with successive
bindings, though some formulations of a query may be much more
efficient than others.

[1] http://www.w3.org/2004/05/06-Algae/#resultSet
[2] http://www.w3.org/2004/05/06-Algae/#doc-algae-askStr
[3] http://www.w3.org/2001/sw/DataAccess/rq23/#query
[4] http://www.w3.org/2004/10/04-pharmaFederate/

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Received on Wednesday, 19 January 2005 04:28:55 UTC

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