Re: Persistant graphs

From: Bill Spight (bspight_at_pacXbell.net)
Date: 10/06/04 

Date: Wed, 06 Oct 2004 00:13:27 GMT

projectshave@yahoo.com wrote:
>
> I'd like to do some graph rewriting in Prolog, which will involve lots
> of addition/deletion of nodes and edges. If a rewrite "fails", it must
> backtrack to the original graph and attempt a different rewrite. A
> persistant, or functional, graph would work best in this case. Is
> there a library for persistant graphs available for Prolog somewhere?
> I'm hoping to avoid the assert/retract global space.
>

Make the graphs terms and carry along the different versions of the
graph being rewritten as arguments. Do not use assert and retract. That
may take a lot of memory, but memory is cheap these days.

For instance, you might represent the graph as a list of nodes
(vertices) along with their immediate successors. Like so:

Graph = [Node - Successors | Nodes]

Then you might have a predicate

rewrite(Graph0, Graph) :- ....

Best wishes,

Bill

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