Path: utzoo!mnetor!uunet!husc6!hao!ames!amdahl!nsc!joe
From: joe@nsc.nsc.com (Joe Caporaletti)
Newsgroups: comp.software-eng
Subject: Re: Is it Art or is it Engineering
Message-ID: <4975@nsc.nsc.com>
Date: 19 Feb 88 21:13:59 GMT
References: <6879@agate.BERKELEY.EDU> <4618@teddy.UUCP> <635@cresswell.quintus.UUCP> <4620@teddy.UUCP> <32637UH2@PSUVM>
Reply-To: joe@nsc.UUCP (Joe Caporaletti)
Organization: National Semiconductor, Sunnyvale
Lines: 44

Virtually every engineering displine of the industrial revolution
relies on the analytical concept of functional decomposition.  A system
is decomposed into processes with well defined input/output effects
on other processes.  This partitioning is the basic technique for
handling complexity by allowing each processes to be understood
separately.

Software is distinguished from other engineering disciplines by
the necessity to specify algorithms as a SEQUENCE of simple
one word operations.  This is necessary since there is only one
central processing unit which can operate on the data in memory.

Functional decomposition is used in software as an analytical tool
(e.g. data flow diagrams).  However, efficient implementation requires 
sequencing of operations.  Therefore, the functionality is transformed 
to a sequenctial algorithm.  There is no simple set of rules for doing this.
Although there has been a lot of good research on program proving,
there is yet no practical formalism for showing that a particular sequencing
of operations is functionally correct.

The complexity and unprovable nature of the of the transformation from 
functionality to sequential algorithmic implementation is unique to software.
For example, although a hardware designer has many options for the 
implementation of some particular combinatorial logic function, the 
engineer must use standard mathematical techniques (e.g. Boolean Algebra) 
to prove that the choosen implementation matches the desired functionality.
While software walk-throughs are a great idea, they are really a 
hand-waving substitute for a formal proof.

In other engineering disciplines like mechanical or chemical engineering,
a great deal of research goes into proving the reliability and
repeatability of the basic processes and principles on which they rely.
When software can apply the same kind of research to everyday problems, it
too will be an engineering discipline.  This is probably several years off
and will require a sophisticated degree of automated assistance to the
process of program transformation.

Knuth knew exactly what he was doing when he named his series "The Art of
Computer Programming."


Joe Caporaletti
Software Engineering and Tools Specialist
National Semiconductor