Subject: Re: e-mail discussion on review report
From: Wolfram Putzke Roeming (Putzke@offis.de)
Date: Thu Mar 16 2000 - 02:18:47 PST
Peter Ashenden wrote:
> Wolfgang Nebel wrote:
> >
> > Both need extensions:
> > - e.g. SUAVE: entity/architecure objects,
> > - e.g. Objective VHDL: genericity.
>
> I agree that design entities can be considered as a form of class in an
> object model, but I am yet to be convinced that entity/architecture
> inheritance is a useful thing. This is honest scepticism - if it is
> proven to be useful, I will happily work towards including it in the
> language.
>
> So far, the examples I have seen have been small and could equally well
> be expressed using component instatiation. The register augmented with
> enable could well be expressed as a composition of a register with a
> tristate gate.
>
> The power of inheritance in OO data modeling comes from two aspects:
> reuse and polymorphism. You define a superclass and a subclass.
> Inheritance allows you to reuse aspects of the superclass in the
> subclass. Polymorphism allows you to define polymorphic objects, and
> either treat them uniformly as objects of the root class, project them
> to specific subclasses, or dynamically bind using their specific class.
>
> The proposal for inheritance in design entities only promises reuse
> benefits; there are is no corresponding polymorphism. I question the
> amount and cost of reuse that can be achieved in practice. The
> difficulty lies in what is inherited, overridden or added when defining
> a derived architecture.
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.
Unfortunaltely they didn't publish their examples and as fas as I know
the company does not exist anymore.
Best regards,
Wolfram
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