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From: mcgregor@hemlock.Atherton.COM (Scott McGregor)
Newsgroups: comp.software-eng
Subject: Re: Reusability considered harmful??(!!)
Message-ID: <34484@athertn.Atherton.COM>
Date: 20 Feb 91 00:55:06 GMT
References: <88637@tut.cis.ohio-state.edu> <88431@tut.cis.ohio-state.edu> <6108@stpstn.UUCP> <1127@TALOS.UUCP> <1991Feb18.224524.28236@cbnewsm.att.com>
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Reply-To: mcgregor@hemlock.Atherton.COM (Scott McGregor)
Organization: Atherton Technology -- Sunnyvale, CA
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In article <88637@tut.cis.ohio-state.edu>, ogden@seal.cis.ohio-state.edu
(William F Ogden) writes:

> I say that if you really want reusable software components, then
> you're going to view a spec for a sine routine that doesn't include
> error tolerances (or execution times, etc.) as simply inadequately
> specified.

The flip side is that if data books are swamped with too much special
case information then they
may be overly complex to read and retrieve information from.  If that
occurs, the market may
indicate its preference for less complete information but easier to
read.  Moreover, the 
consumer may think in terms of a specific application question, and may
not know how that
translates to the general design specs.  E.g. User wants to know how
fast will the spec'ed car
go 0-60 while pulling a trailer weighing 1000 lbs; Datasheet only gives
engine displacements.
 
So, the consumer may not always be knowledgeable enough to convert the
general specs to their
application specific needs-- and the designer may not forsee all
possible applications.  The market
may need to mature significantly, and both consumers and designers
become more educated about
each other for a considerable amount of time before this kind of reuse
becomes pervasive.

> 
> #Do you buy a car without a test drive?  Do you buy a suit without trying
> #it on?
> 
> For peace of mind, you may want to take it out for a test drive, but
> you really can't afford to test whether it meets all its specs. Do
> you check the oil capacity, the generator output, the compression ratio,
> the horsepower rating, etc.? When buying clothing, do you check the 
> durability, colorfastness, shrikage, wrinkle resistance, etc.?

When someone buys a *fleet* of cars, they often *do* independent tests,
or pay for consulting from independent testing labs (Consumer Reports,
Road & Track...), that sometimes individuals do not do.  Similarly,
before purchasing large amounts of clothing appropriate features may be
frequently tested.
Important aspects determining whether products are pretested or not
include the product price, and
the number purchased, or amount of use.  Most software systems under
discussion here are large,
and are big ticket items from a product price standpoint.  They may be
used many times.  Purchasers
are often corporations who may indeed require some presales proof of
suitability before buying the
software.  It  is thus important for  the developers who reuse the
software to prove to themselves
that the inherited software they used works as expected--before an
embarassing situation is
discovered by a prospective customer. 

Scott McGregor
Atherton Technology				mcgregor@atherton.com