Re: Structuring the discussion points

[Martin Fabian <fabian@s2.chalmers.se>]

>What I consider sensible as minimal graphical attributes:
> - position of the center for transitions and places.
<snip>
>Do we want to store offsets or absolute positions?
>
Should this be specified at all in the format?
If relative coordinates are used, then the question is "relative to what?"
And if the answer is "upper/lower left/right corner" then those coordinates
are absolute, right?

>>         * meaning of different arcs
>>           (normal, inhibitor, read, ... (which else))
>  flexible arcs (multiset valued)
>I know that several formalisms do not need to indicate
>flexible arcs explicitly.
>
"Normal" includes "weighted"? 
I certainly think that all arcs should be weighted, but optionally and with
a default weight of one.

>>         * labels as pure text
>>           (the developers are free to substructure the labels,
>>            but a pure text of a label is required, too)
>
We should distinguish between "label" and "name" (where necessary). Each
pn-element (at least transitions (and places?)) may have both a label _and_
a name. For instance, for transitions, the label may be related to an
event, which need not be unique between transitions (several transitions
may be labeled by the same event). The names must be unique, though. 

This brings up the question of an "alphabet". In our use of pns, each net
has an alphabet, the elements (the "events") of which label the
transitions. This is something we find useful and necessary. 

What about time?
We would need both P-timed and T-timed nets. Also, there's interesting work
going on at http://www.cs.chalmers.se/Cs/Research/Algorithms/ (see "A
Decision Support System for Scheduling a Shop Floor Work Center") with
"arc-timed" nets, where the time is assoicated with (in this case) the
output-arcs. Simplifies lots of things (though expressitivity is the same,
of course).

///////////////////////////////////////////////////////////////////////////
Martin Fabian, Associate Professor                    fabian@s2.chalmers.se
Control and Automation Laboratory         http://www.s2.chalmers.se/~fabian
Department of Signals and Systems
Chalmers University of Technology                  tel: +46 (0)31 772 37 16
SE-412 96 Göteborg                                 fax: +46 (0)31 772 37 30
Sweden