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From: macrakis@harvard.ARPA (Stavros Macrakis)
Newsgroups: net.lang,net.lang.st80
Subject: Re: Definition of Buzzwords: "Object-Oriented"
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Date: Tue, 22-Jan-85 17:27:55 EST
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Posted: Tue Jan 22 17:27:55 1985
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> Is there a definition of the term "object-oriented" which is both descriptive
> of all current uses of that term and accepted by all who currently use it?
>                                         Bill Laubenheimer ucbvax!wildbill

`Accepted by all who currently use it' is harder than `descriptive'....

Let me propose:

  An object-oriented language/system considers its behavior to be
  defined in terms of the behavior of smaller units (called
  `objects') each of which has a repertoire of operations
  applicable to it.  The object operations are the only operations
  which normally have access to the underlying implementation of
  the object.  Almost all object-oriented systems organize objects
  into classes of different individual objects which share the
  same repertoire of operations, and these classes can normally
  have subclasses which inherit the operations of the classes and
  add more classes.  Almost all object-oriented systems allow (and
  encourage) objects to have internal state which changes with time.

This definition emphasizes the differences with other language
qualities, such as `algorithmic' (Algol, Fortran, Pascal, C, Snobol,
APL), `functional' (Lisp, FP, APL), `backtracking' (Snobol, Planner,
Prolog), or `string-oriented' (Snobol, Trac, Teco); but note that the
qualities are not exclusive.  Too often, spurious questions on the
order of `is it algorithmic or is it object-oriented' cloud the
question.  A serious question, however, is whether changing state is
important to object orientation.  Perhaps this is the difference
between data abstraction and object orientation?  Or is object
orientation just the fashionable name for data abstraction?

A more historically-oriented definition might be:

  Object-oriented languages/systems are inspired by Simula 67.

Note that it is not important to these definitions whether the
language is part of an interpretive system (like Smalltalk), nor is
the inheritance mechanism central (of course you can argue that a GOOD
object-oriented system has a certain kind of inheritance mechanism).

By these definitions, Simula 67, CLU, Smalltalk, Objective C, Ada, and
ZetaLisp are all object oriented.  They do differ.  Some enforce the
access restrictions of the class, others don't; some have
sophisticated (or just plain complicated) inheritance mechanisms,
others don't.

But I think it would be unfair to frame a definition which excluded
any of these languages.

	-s