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Re: What databases have taught me

From: J M Davitt <jdavitt_at_aeneas.net>
Date: Sat, 24 Jun 2006 02:36:27 GMT
Message-ID: <Ly1ng.66111$mh.20139@tornado.ohiordc.rr.com>


Dmitry A. Kazakov wrote:
> On Fri, 23 Jun 2006 16:31:02 +0200, Bruno Desthuilliers wrote:
>
>

>>>What kind
>>>of operation do you think is unsupported by the algebra ?
>>
>>I don't know how this translates in english, the french term is
>>"fermeture transitive d'un graphe". IOW, if I have (minimal example):

>
>
> Transitive closure of?
>

Directed, acyclic graphs.

Date and Darwen say TCLOSE - their operator denoting the transitive closure operation - on a binary relation having attributes of the same type yields a superset of that relation if there exists a sequence of values representing a path. [My paraphrase.] Given an appropriate relation R, TCLOSE R would contain {x, y} if either {x, y} exists or there exist some {x, a}, {a, b}, {b, ...}, {..., y}.

There is, as far as I know, nothing for networks. Received on Fri Jun 23 2006 - 21:36:27 CDT

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