Path: utzoo!attcan!uunet!cs.utexas.edu!helios!chandra
From: chandra@cs.tamu.edu (Chandrasekaran Periannan)
Newsgroups: comp.lang.prolog
Subject: Re: Need help in the differences between RDBMS and Expert Systems
Keywords: RDBMS, Expert System
Message-ID: <6675@helios.TAMU.EDU>
Date: 18 Jul 90 23:41:47 GMT
References: <1990Jul17.201309.5974@cbnewsh.att.com>
Sender: usenet@helios.TAMU.EDU
Organization: Computer Science Department, Texas A&M University
Lines: 35

>When I look at most of the Expert System Shells they provide a
>syntax for representing the domain specific data (or knowledge)
>and a way to use the data (conditional knowledge or inference 
>mechanism). Can't the same thing be achieved with tables and
>queries in a RDBMS. Is the chaining through conditional knowledge
>possible in ES is missing in RDBMS?
>
>I always have trouble in explaining the differences between the
>two when someone asks. I have heard people saying relational
>algebra cannot do recursion (I don't know what this means). 
>I would appreciate any clarification on this from the netters.
>
>Thanks.
>


	Relational algebra cannot do recursion in the
sense that it cannot compute the transitive closure
of a relation; i.e., there is no relational algebra
query of finite length that expresses the closure of
a relation.

	I know almost nothing about expert systems;
but I would presume that they usually provide the
facilities similar to Prolog in which you can express
recursive queries, which is all that you need for
expressing the closure of a relation.

	Actually you don't need the power of Prolog
to compute the closure, but only a strict subset of it,
namely, datalog.

chandra.
chandra@sparc45.tamu.edu
chandra@photon.tamu.edu