Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!uunet!dino!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!m.cs.uiuc.edu!p.cs.uiuc.edu!johnson
From: johnson@p.cs.uiuc.edu
Newsgroups: comp.sw.components
Subject: Re: What should a component library loo
Message-ID: <130200020@p.cs.uiuc.edu>
Date: 15 Nov 89 17:35:14 GMT
References: <89@<DWIGGINS>
Lines: 23
Nf-ID: #R:<DWIGGINS:89:p.cs.uiuc.edu:130200020:000:1285
Nf-From: p.cs.uiuc.edu!johnson    Nov 14 09:52:00 1989


dwiggins@atsun.a-t.com asked "What should a component library look like"?
In particular, he said "It seems to me that separation of functional
specification from implementation is at least a Good Thing, if not 
absolutely necessary for a viable library.  This would allow a variety of
implementations that meet the spec, and that vary in their performance
details (memory, speed, language, operating system, etc.)."

This is a very common claim.  I disagree with it.  This is only important
in a library of data structures, which will eventually be a minor part of
component libraries.  Take a user interface library, for example.  There
is no need to have a variety of implementations that meet the spec.
I think that data structure components are the exception rather than the
rule.  Most of the code that we write is not heavily dependent on 
algorithms, and so performance will not be a big deal.

Specifications are important because they help the potential reuser
to understand the component.  Thus, they are very important.  However,
I don't buy the idea that we will need lots of implementations that
meet the same spec.  And yes, I've read Booch's "Software Components
with Ada".  It is all about data structures.

Ralph Johnson -- University of Illinois at Urbana-Champaign