Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!uwm.edu!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!m.cs.uiuc.edu!johnson
From: johnson@m.cs.uiuc.edu
Newsgroups: comp.sw.components
Subject: Re: What is a reusable software compone
Message-ID: <71800004@m.cs.uiuc.edu>
Date: 28 Jul 90 04:41:00 GMT
References: <27705@athertn.Atherton.COM>
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Nf-ID: #R:athertn.Atherton.COM:27705:m.cs.uiuc.edu:71800004:000:1241
Nf-From: m.cs.uiuc.edu!johnson    Jul 27 23:41:00 1990


I think that Paul Sander's B-tree abstraction is a pretty good
reusable component.  However, I think that Bill Ogden has a
good point.  Bill's basic point is that it is really more
important to reuse specifications than it is to reuse
implementations.  Of course, we need to provide implementations
for our specifications, but the user should think mostly of the
specification and not the implementation.  B-trees are an
implementation, while almost-constant functions are specification.

Further, I take the point of view held by the object-oriented
community that it is not particular kinds of components that are
important, but rather sets of components and their relationships.
The advantage of concentrating on specification is that you end
up with lots of components that share the same specification.
When you learn one, you have learned something about all of them.
Also, it becomes easier to replace one component with another
because they will share specification.  Thus, it becomes easier
to write utilities that work with any of the related components.

This is not all that relevant to Paul's original article, but I
saw a soapbox, and couldn't resist getting on it.

Ralph Johnson -- University of Illinois at Urbana-Champaign