constraints

Stephan Diehl (diehl@cs.uni-sb.de)
Fri, 16 May 1997 11:43:33 +0200

I have looked into papers about Amulet, Garnet and VB2,
on DeltaBlue and SkyBlue, ...

Now I have a bunch of questions:

1) Is it true, that SkyBlue cannot handle pointer variables ?
2) Do pointer variables correspond to SFNode fields in VRML ?

If the answer to both questions is YES, then Garnet's
one-way constraint model seems to be the answer. But
then there is the problem of how to implement constraints
with VRML 2.0 and JavaScript-Scripts or Java-Scripts.

Currently in VRML 2.0 fields of type SFNode the
value NULL or a pointer to a node (object) is stored.
To use Garnet's constraint solving mechanism we have
to attach to each field additional information:
outofdate : indicates if the value of the field is out-of-date
dependencies: list of fields which depend on this one
eval: a method (constraint) to compute this field's value
timestamp: number of times "eval" was executed

3) How do we attach this information ?

Now the idea is, that if a value of a field is changed
the values of all fields depending on it are recomputed.

4) How do we get the information, that a value has
changed? We cannot expect VRML programmers to
use only our function to access and modify fields !

Cheers
-- Stephan

---------------------------------------------------------------
Dr. Stephan Diehl Tel.: ++49-681/302-3915
EMAIL: diehl@cs.uni-sb.de WWW: http://www.rw.cdl.uni-saarland.de/private/diehl
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