Re: How to handle processes that must occur

Quoting Drew McDermott <drew.mcdermott@yale.edu>:

> > [Jeff Dalton]
> > 
> > Would it skip?  I'd have thought, perhaps naively, that in a
> > sequence,if a precondition of a step was not satisfied, then
> > execution could not advance beyond that point.  The execution
> > engine would do something such as wait, or signal an error,
> > or ask someone what to do.
> 
> You're assuming that the execution engine can check whether an
> arbitrary precondition is true.

Ok, but suppose it can't check.  It still wouldn't skip the step.
It would assume the step could be executed and would try to execute
it or, if quite conservative, it would assume the condition was false
and refuse to execute it without authorization.

Either way, it wouldn't skip the step and just go on to the next
step in the sequence.

Also, doesn't a sequence mean that a step can't execute untill
the earlier steps have executed?  Or in OWL-S does it mean that
steps can be skipped?

> There are other occasions when it might make sense to insert plan
> steps to verify that a condition really holds.  But an agent obviously
> can't do this for every condition, or we'd have an infinite regress of
> steps inserted to verify the preconditions of previously inserted
> steps.  

Not necessarily.  Perhaps a checking regress would terminate in steps
that lack preconditions.  :)

-- Jeff

Received on Wednesday, 21 April 2004 16:47:37 UTC