Re: Learning curves and such (was Re: pgFoundry)

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Date: Tue, 17 May 2005 01:32:03 -0400

> As against that I notice some new arrivals proposing to add deductive
> reasoning to Postgres:
> http://archives.postgresql.org/pgsql-hackers/2005-05/msg01045.php
> or implement SQL99 hierarchical queries:
> http://archives.postgresql.org/pgsql-hackers/2005-05/msg01089.php
>
> I might be wrong, but I'll bet lunch that neither of those projects will
> come to anything. You can't run before you learn to crawl.

The main advantage of deductive reasoning implementation I propose
is in fundamental extension of database query language, I don't propose
to extent SQL with some cumbersome constructions, for example, like WITH
to express recursive queries (inefficiency of such constructions can be easily
seen if you try to express a bit more complex recursive query then finding
ancestors, e.g. query which finds minimal paths).

Also it should be mentioned that original query language (SQL) de facto
remains without great changes, the logic program which defines predicates
(intensional relations) is located in the system table (there can be put
the name and both the text and inner code of logic program). When we want
to get intensional relation we simply write in SQL query the name of the
logic program (deductive database) and the name of the predicate with the
list of arguments. This syntax is identical to the syntax of table function
calling with the schema name.

Regards, Dmitriy