Re: c.d.theory glossary -- definition of "class"

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Wed, 23 Jun 2004 01:40:57 +0200
Message-ID: <40d8c389$0$563$e4fe514c@news.xs4all.nl>

Alan wrote:

> Dawn M. Wolthuis wrote:

>>mAsterdam wrote:
>>>Glossary 0.0.4:

<snip>
>>>[Class]
>>>A class is what provides a name and a place for
>>>the abstract behavior of a set of objects
>>>said to belong to the class. (Larry Wall, Apocalypse 12)
>>>
>>>note:
>>>Other definitons welcome, this goes for the rest as well,
>>>of course.
>>>
>>>Some use 'class' as having exposed data.
>>>Please be explicit about this if you do so.
>>
>>I really don't like the "A class is what ..." definition,
>>especially since folks like Date keep asking why the OO
>>folks are so confused on what a class is -- is it a
>>variable, for example? I would like to make it clear that it
>>is metadata. I don't just mean that the source code for the class is
>>metadata -- the class is metadata. Here is a definition I just read in
>>Systems Analysis & Design: An Object-Oriented Approach with UML by Dennis,
>>Wixom, and Tegarden
>>
>>"A class is the template we use to define objects."

> 
> I agree. "Class" is often confused with "Instance" of a class. 
> Class is the template, and the class is _instantiated_ when
> an object that belongs to that class is created. 
> For example, we tend to forget that Windows is OO.
> A "text box" control that you place on a form is an instance
> of the "text box" class. This class has properties,
> which are in the template, many of which can be specified
> in the properties tab. The properties are specifiable for
> each instance of the class.

Some properties are class-level. Having said that, I've never seen an actual serious misunderstanding grow from this supposed confusion. It is important in the initial learning stage, no doubt.

>>This leaves the meatier definition to "objects"
>>but at least it states more clearly what
>>a class is.

>
> An object is an instance of a class or subclass.

A record is an occurrence of a recordtype. A performance is the incarnation of a composition. A building is the realization of a design.

These are statements about structural relations, not definitions. Received on Tue Jun 22 2004 - 18:40:57 CDT