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From: mwm@ucbtopaz.CC.Berkeley.ARPA
Newsgroups: net.lang.st80
Subject: Re: Definition of Buzzwords: "Object-Oriented"
Message-ID: <689@ucbtopaz.CC.Berkeley.ARPA>
Date: Wed, 30-Jan-85 01:26:53 EST
Article-I.D.: ucbtopaz.689
Posted: Wed Jan 30 01:26:53 1985
Date-Received: Sun, 3-Feb-85 11:02:09 EST
References: <4288@ucbvax.ARPA> <366@cavell.UUCP> <769@loral.UUCP>
Reply-To: mwm@ucbtopaz.UUCP (Praiser of Bob)
Distribution: net
Organization: Univ. of Calif., Berkeley CA USA
Lines: 60
Summary: 

Since we're into definitions, let me present my favorite version. This is
from (I think - everything is stacked away in boxes) Tim Rench's SNot paper
already mentioned here.

Examples are not meant to reflect any real language.

'Data Encapsulation' - Provides modules, and data objects that only functions
in the appropriate module can touch. For instance:

	MODULE IntStack is Push, Pop ;
		STRUCT Stack is ... ;
		PROCEDURE Push is ... ;
		PROCEDURE Pop is ... ;
		END IntStack ;

	x is IntStack ;
	y is Int ;

	x.Push(10) ;
	y := x.Pop() ;

'Data Abstraction' - An improved form of encapsulation, wherein the abstraction
can be reused on different data types. For instance:

	MODULE Stack(T is TYPE) is Push, Pop ;
		... ;
		END Stack ;

	MODULE List(T is TYPE) is ... ;
		END List ;

	x is Stack(Int) ;
	y is Stack(List) ;
	z is Int ;
	w is List ;

	x.Push(10) ;
	y.Push([a, b, c]) ;
	w := y.Pop() ;
	z := x.Pop() ;

Finally, a programming language is 'Object Oriented' if *everything* must
be encapsulated. In other words, Concurrent Euclid is 'Object Oriented,'
and provides encapsulation, but not abstraction. Smalltalk is 'Object
Oriented,' and provides abstraction. CLU is not 'Object Oriented,' but does
provide abstraction.

I prefer this definition because it gives a high degree of resolution when
you want to talk about a language (admittedly, it takes a lot of buzz
words).  This would be far better than allowing 'Data Encapsulation' to
disappear and 'Data Abstraction' and 'Object Oriented' to become synonyms.

I think it even correctly captures the methodology split the smalltalk
people like to talk about. If everything is in a module, then all data has
a set of routines (messages) that can be used on it, and all routines have
a set of data they are associated with. This should make thinking about
things as data objects that reply to messages easier.  Of course, whether
the methodology gets used depends on the programmer.

	<mike