Re: Question about OWL-S sequence

> > [Drew McDermott, i.e., me]

> > 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))

> [Jeff Dalton]
>
> O-Plan and other Edinburgh planners have used something like
> that for many years.  For example:
> 
>   nodes
>     1 action {fuel_vehicle ?v},
>     2 action {check_vehicle ?v},
>     3 action {brief_drivers ?v},
>     4 action {move_vehicle ?v ?a};
>   orderings
>     1 ---> 4, 2 ---> 4, 3 ---> 4;
> 
> It's not always easy to read, but sequence notations can be
> applied to the tags, e.g. (inventing a symtax that's not in
> O-Plan):
> 
>   (sequence (parallel 1 2 3) 4)
> 

> > [me]
> > 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))
> 
> > However, I ran this by other OWL-S mavens in a recent telecon and they
> > gagged.

> [Jeff]
> Did they gag on the DAG idea or only on the parallel / sequence
> example above?

I believe only on the occurrence of the same process invocation in
more than one 'sequence'.

> [Jeff]
> I was thinking of something more like this:
> 
>   (tags 
>       (tag A (arf))
>       (tag B (barf))
>       (tag C (scarf))
>       (tag D (darth))
>       (tag E (earth))
>     (sequence A B D E)
>     (sequence B C)
>     (sequence A C E))
> 

They're equivalent if you translate to RDF.  The tags become rdf:ID's.
When you undo the abbreviations and translate everything to triples,
you get the same thing from my 'parallel' example above as you would
from this:
   
   (parallel (tag A (arf))
             (tag B (barf))
	     (tag C (scarf))
	     (tag D (darth))
	     (tag E (earth))
	  (sequence A B D E)
          (sequence B C)
          (sequence A C E))

except that we've now introduced an ID for the occurrence of (darth)
that we didn't need before.  It's not syntactically the same, but it
is semantically, because 'parallel' imposes no constraints on its
arguments.  (This point may seem odd but it is true if the semantics
of 'parallel' is that it starts when the first arg starts and ends
when the last arg ends.  And what else could it be?) 

                                             -- Drew

-- 
                                   -- Drew McDermott
                                      Yale Computer Science Department

Received on Thursday, 20 May 2004 14:51:06 UTC