Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!husc6!mailrus!umix!uunet!mcvax!cernvax!cui!dt
From: dt@cui.UUCP (TSICHRITZIS Dennis)
Newsgroups: comp.lang.c++
Subject: Object Design Tools
Message-ID: <97@cui.UUCP>
Date: 18 Feb 88 20:39:22 GMT
Organization: University of Geneva/Switzerland
Lines: 79
Posted: Thu Feb 18 20:39:22 1988

We have been struggling for a year now to understand what kinds of
tools are needed for object design.  Here are some comments which may
at least encourage some discussion.

General comment
---------------

If you insist on reusability you cannot always rely on structured
design by refinement.  At some point you should synthesize from
existing objects.  Traditional software methodologies are the
equivalent of a cookbook recipe.  Given the desired meal, you come down
to the needed ingredients and the procedure to follow to cook it.
With object reusability the problem is inverted.  Given some notion of
a meal and some available stuff in your fridge, fix a reasonable meal.

Here are some tools that we have been working on that we believe will
help to solve the problem:

1. The first tool you need is one that helps you to organize a software
base of available objects.  Conceptual modeling and knowledge base
ideas are helpful here, but we are dealing with *real* objects, not
concepts.  Together with this we need a powerful filter-browser to
select the pertinent objects for your application.

2. Another tool you need is a structure editor like the ones used for
VLSI design, which puts objects together from existing objects as
parts.  You can go so far with structural synthesis.  Eventually you
arrive at some objects which are relatively autonomous.

3. You need a configuration tool which defines how objects are put
together.  The important notion here is "glue".  Glue  is a kind of
interfacing tool which you use when objects do not fit nicely
together.  After all, if you insist on reusing objects you will be very
lucky if they can talk to each other.  A common standard interface as a
uniform glue is too restrictive.  The problem we are struggling with is,
what are the most useful kinds of glue?  A more advanced problem is,
what is a good tool for creating your own glue?

4. When objects are active and autonomous, you need a notion of
"scripting".  Scripts can be thought of as scenarios in a theatrical
play, or as the instructions given by the coach to the football players
for a game.  They can be considered as a driving mechanism, or as a
constraint mechanism on a set of objects.  We have worked on scripts and
we are now developing some tools.  It is a fascinating area.  What we
are aiming for is that the scripts which coordinate objects will be the
same as the ones which can coordinate an animation of characters
representing objects.  In this way the user can follow what the objects
are doing by watching the animated characters.

The work we are doing relates to Hybrid, a local, yet another,
object-oriented language and system.  However most of the work is in
C++, and the design tools should apply to other environments.

By the way, if you want to understand how application developers may be
using existing objects to create applications, go and watch a mason
building a *stone* wall (if you can find anywhere such an endangered
species).  You will see there the notions of a software base, available
objects, selection of objects, fitting of objects, mortar as glue,
etc.  The striking impression is that for such an effort you need
imagination, not discipline.  That sort of goes against traditional
thought about what programming ought to be.  But I better stop here.

To illustrate that no problem is new, here is a correspondence between
hacking, and object design and configuration.

Object design				Hacking
-------------				-------
select objects from software base	get packages from network
modify them				hack them
configure via scripts			link with shell commands
monitor behaviour			prototype & test
evolve software base			distribute on the network

You get the feeling that what we are trying to do is to provide some
academic respectability for hacking.

Greetings from Geneva.

D. Tsichritzis          (UUCP: mcvax!cernvax!cui!dt)