Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!mcvax!enea!sicsten!alf From: alf@sicsten.UUCP (Thomas Sj|land) Newsgroups: net.lang.prolog Subject: Re: Depth First Iterative Deepening in parallel PROLOGs Message-ID: <1167@sicsten.UUCP> Date: Tue, 10-Jun-86 22:29:29 EDT Article-I.D.: sicsten.1167 Posted: Tue Jun 10 22:29:29 1986 Date-Received: Sat, 14-Jun-86 06:45:23 EDT References: <236@ecrcvax.UUCP> Reply-To: alf@sicsten.UUCP (Thomas Sj|land) Organization: Swedish Institute of Computer Science SICS Lines: 19 Keywords: DFID DFPD OR-parallel Horn-Clause-Provers Summary: DFPD is bad but useful as a reference for "smarter" schemes. I agree with earlier statements that DFPD is rather useless as an approach for or-parallel logic programming systems. It has one interesting point though: It is hard to think of an or-parallel scheme which has a simpler implementation than this one. The needed communication is minimal and the variable representation is optimal ( = Warren's for instance). The price you pay is reexecution. In all other schemes I have seen (in our lab there is work going on considering a handful (sic!)) there are considerable measures taken as to either reach a highly flexible variable representation (Haridi/Ciepielweski /Hausman proposes hashing etc.) or trying to avoid copying through more or less smart heuristics or even specialized hardware (Khayri/Fahlen/Karlsson). All of these schemes involve a considerable amount of communication, at least compared to DFPD. An implementation of a DFPD Horn Clause prover ("pure Prolog") could show useful in the sense that any proposed "smart" scheme has to be at least as good as the DFPD scheme (for at least some subclass of programs and queries) to be taken seriously. It is also interesting to notice that DFPD is complete, whereas most of the "smarter" schemes are not.