Re: Question about OWL-S sequence

> > [me]
> > I don't know.  We're in the zone one often winds up in when using
> > ontology to implement syntax.  Suppose I wanted to write a sentence
> > using the same occurrence of the word "winds" as in the first sentence
> > of this paragraph.  Not the same word, the same _occurrence_.
> 
> [Jeff Dalton]
> Why is that the right analogy?  

Actually, I am now willing to waffle.  My analogy was completely apt
as an explanation for why it seemed at first to make no sense to put
the same occurrence in two sequences.  We _have_ been thinking of the
RDF encoding of (sequence A B C) as more or less an encoding of its
syntax.  But since I did admit up front that we _could_ add arbitrary
DAGs, it's clear that we could think of "occurrences" as nonsyntactic
objects. 

Just to play with that case, here's a syntax for an arbitrary DAG:

(DAG (tag A (arf))
     (tag B (barf))
     (tag C (scarf))
     (tag D (darth))
     (tag E (earth))
  (A -> B -> D -> E)
  (B -> C)
  (A -> C -> E))

and imagine an RDF encoding in which the tags are implemented by RDF
IDs.  (RDF encodings are always better imagined than actually seen.)
Now the IDs don't refer to occurrences of terms; they refer (very
indirectly) to events that occur whenever an occurrence of (an event
corresponding to) the DAG occurs.

In fact, given this distinction, we can now bounce back to the
original sequence notation (e.g., (sequence (arf) (barf) (scarf))) and
reinterpret with this different convention.  We could write the DAG
above thus:

   (parallel (sequence (tag A (arf)) (tag B (barf)) (darth) (tag E (earth)))
             (sequence B C)
             (sequence A (tag C (scarf)) E))

In fact, this is essentially the syntax we used in the (now forgotten)
action-expansion notation of PDDL 1.0.  (Which had a formal semantics,
included in the appendix to the PDDL 1.0 report.)

However, I ran this by other OWL-S mavens in a recent telecon and they
gagged.  So stock up on dramamine before trying to make sense of all
this.

                                             -- Drew

-- 
                                   -- Drew McDermott
                                      Yale Computer Science Department

Received on Wednesday, 12 May 2004 22:51:31 UTC