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Re: Query and storage

From: Thomas B. Passin <tpassin@comcast.net>
Date: Fri, 24 May 2002 08:18:00 -0400
To: www-rdf-interest@w3.org
Message-id: <000a01c2031d$0c499900$0bf13044@tbp>
[Dave Reynolds]

> The normal semantics of variable bindings is to return all the
combinations of
> variable bindings that apply. This leads to combinatoric expansion in some
> cases.
> To give a concrete example. I have a simple data set where there are
> properties that have multiple values (these are things like comments,
> annotations and ratings by a collection of users of some set of content
> If I just want the values of one property or the values of all properties
> reponse-as-query-binding works fine. However, suppose I want to retrieve
> value of a specific set properties, such as:
>    ?x ep:comments ?c &
>    ?x ep:annotations ?a &
>    ?x ep:ratings ?r

I think this is a matter of what your query asks for.  Your example is not
well posed.  In sql you would proabably do it with three queries that get
UNIONed together.  You don't really want one tuple where c,a, and r all
appear in the same tuple.  You may in fact only want to get back ?X,
depending on your needs.  If you pose the question correctly, the
combinatorial explosion goes away.

This scenario could provide good guidance in the design of the query
language, but I don't see it as having anything to do with variable binding
vs subgraph results.


Tom P
Received on Friday, 24 May 2002 08:17:33 UTC

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