Re: e-mail discussion on review report

Subject: Re: e-mail discussion on review report
From: Peter Ashenden (petera@cs.adelaide.edu.au)
Date: Thu Mar 16 2000 - 15:38:56 PST

Wolfram Putzke Roeming wrote:
>
> I'd like to remember to the VISTA Technologies OO-VHDL proposal.They provide
> polymorphism for entity objects. In their paper in IEEE
> Computer 10/95 they claim to have modelled some "larger" examples
> with their entity object approach. The paper also contains some quantification
> on the benefits for reuse etc. that they have measured.

The Vista OOVHDL approach was to define methods in entities, similar to
the way in which you did in Objective VHDL. In inherited architectures,
they allowed overriding of methods. This is different from inheriting
structure and implicit connection of processes to signals via drivers.

Vista OOVHDL instantiated entities as EntityObjects, and allowed
invocation of methods as remote procedure calls. They also had
EO_Handles, which are polymorphic references to entities. However, the
form of polymorphism was unconstrained - an EO_Handle could refer to
*any* entity, not just those of a particular entity declaration or its
derivatives. Thus the approach relied on dynamic checking that the
objected pointed to by a handle was in the required hierarchy - it
couldn't be determined statically.

We included Vista OOVHDL in our early survey of proposed OO extensions
to VHDL, and drew attention to the problems in the Vista approach. See:

http://www.cs.adelaide.edu.au/users/petera/suave/oo-vhdl-viuf-spring-97.pdf

> Unfortunaltely they didn't publish their examples and as fas as I know
> the company does not exist anymore.

Indeed. I think the work they did was on a US government research
contract, and never got transferred to industry. I don't know what
happened to the people at Vista who did the work. They have never been
involved in, nor communicated with, the IEEE OOVHDL study group, so far
as I am aware.

Cheers,

PA 

-- 
Dr. Peter J. Ashenden              Email: petera@cs.adelaide.edu.au
Dept. Computer Science                    peter.ashenden@acm.org
University of Adelaide                    peter.ashenden@computer.org
Adelaide, SA 5005                  Phone: +61 8 8303 4477
Australia                          Fax:   +61 8 8303 4366

WWW: http://www.cs.adelaide.edu.au/~petera  (includes PGP public key)

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