Re: PROV-ISSUE-465 (avoid-infinite-inferences): Avoid infinite loops in inferences [prov-dm-constraints]

On Wed, Aug 8, 2012 at 10:47 AM, James Cheney <jcheney@inf.ed.ac.uk> wrote:
> I understand your concern.  At a purely technical level, we avoid nontermination, but only by drawing a fine distinction between having an entity(e) statement in the instance, and "knowing e is an entity" (represented by entity' \in typeOf(e)).
>
> We (me, Luc, Paolo, Tom) discussed three ways of avoiding this problem, before finalizing the review copy:
>
> 1.  Drop the entity-generation-invalidation and activity-start-end inferences altogether.
> 2.  Add some limitation to inference (such as your suggestion of not triggering inferences on generated existential variables, or applying the ) that recovers finiteness.
> 3.  [what we have done] demote the type inferences to only infer constraints like 'entity' in typeof(id) , not add new statements like entity(e) to the PROV instance.
>
> Of the three, the one with strongest consensus was (3).  Some of us strongly felt that the e-g-i and a-s-e inferences are needed.  Others, including me, strongly felt that (2) would be a bad idea, as it breaks the connection to logic (i.e., the e-g-i and a-s-e  and may have more radical unforeseen consequences.

OK, I see now that you have thought about this. It would be useful if
some of those considerations shone through to the document. I can
agree on argument 3 if we formulate it well, explicitly.

I agree that the inferences are needed, or at least useful.

> We believed that (3) was an acceptable compromise (if a bit hacky), but, I'm not sure how the group as a whole would feel.  That is why I'm laying out the options we considered.
> So, my proposal would be to make this distinction clearer (and explain why) so that it does not surprise or bite people...

I would think this is the best approach, rather than dropping the
inferences all together, as the rest of the constraints rely on them.

-- 
Stian Soiland-Reyes, myGrid team
School of Computer Science
The University of Manchester

Received on Wednesday, 8 August 2012 10:03:02 UTC