On May 29, 2008, at 6:08 PM, Jan Urbański wrote:
> Now about the idea itself:
> http://www.informatik.uni-augsburg.de/de/lehrstuehle/dbis/db/
> publications/all_db_tech-reports/tr-2001-7_kie_koe/
> tr-2001-7_kie_koe.pdf
> That's one of the basic papers about Preference SQL, explaining
> what it's all about. For those, who don't feel like reading through
> it just because I said it's interesting, here's some more info
> (warning, it's a bit formal):
>
> Preference SQL is an extension to regular SQL, that allows
> expressing preferences in SQL queries. Preferences are like "soft"
> WHERE clauses. A preference doesn't need to be satisfied by a tuple
> for it to appear in the result set, but it's "preferred" it is.
> More strictly, a set of preference clauses in a SQL query defines a
> partial order on the result set as it would appear without any
> preference clauses and then returns the maximal elements.
> The partial order imposed by the set of preferences P[1], P
> [2], ..., P[n] is such that tuple T1 > T2 iff T1 all preferences
> T2 satisfies and there is a preference satisfied by T1 and not
> satisfied by T2 (or there is a preference satisfied by T1 that is
> "better" satisfied by T2 and all others are "equaly" satisfied). As
> can be seen, there could be an order defined on the degree of
> satisfyiness of a preference, and the exact semantics are not all
> that well defined for all concievable cases. Defining a complete
> semantics will be a part of my thesis.
This seems like a subset of http://pgfoundry.org/projects/qbe/ ... or
do I misunderstand?
--
Decibel!, aka Jim C. Nasby, Database Architect decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828
