Hi Alex,

> I've become interested in visual programming languages, but a bit
> disappointed that visual notation tends to be based on topological
> rather than geometrical relationships. 

I think you need to define a little more carefully what you mean
by 'geometrical relationships'. Within the theory of visual
languages community, there are many formalisations that include
information other than node-link connectivity. Check out Marriott
and Meyer's book for an overview of other approaches.

> ... In fact the only example of a
> computer language using geometrical notation I've found is the
> ReacTable and the related TurTan, which use relative orientation and
> proximity of symbols.  Are there others?

Those two systems are from the same research group, and based on
the same ideas. Symbol orientation is a very natural interaction
technique with a tangible interface such as the one this group
have created, but not so convenient when using a mouse.

> Also, perhaps a more interesting question is, why aren't there more?
> I can see why you wouldn't want (practically) continuous parameters of
> distance involved in business logic, but how about programming
> languages for use in the arts?

Well, I guess your examples are both in the arts. What about
other domains? A natural place to look might be interactive
geometry tutors, computer aided design, or any other area where
geometry is significant.

Alan Blackwell
Reader in Interdisciplinary Design, University of Cambridge
Further details from www.cl.cam.ac.uk/~afb21/

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