Pate 62

PG WEEKNAPPLIGATION DEVELOPMENT.

SEPTEMBER 4, 1989

This is the
first in a series
of articles on ob-

new technology
that is changing
tihe way pro-
grammers and.
users deal with
computers.

The modifier
"object-oriented"
is more than just

JAMES
MARTIN a buzzword. It
describes a tech-

nology that's radically changing the user
interfaces and the way computers are
programmed, It reguires a new way of
thinking about. the machine that is, in
fact, totally intuitive. It is a technigue
that holds great promise for dealing
with the ever-increasing complexity of
computer applications.
Object-oriented technigues are having
a significant effect on the way comput-
ers handle complexity. The technigues
are used for encapsulating information,
thereby shielding layers of complexity
from view. Through the use of objects, a
complex problem can be recomposed in
simple components.
New operating environments are
H based heavily on object-oriented user in-
| i terfaces.
| Sophisticated graphics interfaces for
| CAD/CAM and computer-aided software
engineering (CASE) applications are
now possible because of these new tech-
nigues, Word processors and expert-sys-
tem shells are using object-oriented tech-
nigues. Programming languages based
on object-oriented technigues are show-
ing productivity gains o£ 5-to-1 or better
for complex programs. Object-oriented
databases are being designed to handle
complex data modeling and storage in
applications such as CAD/CAM and
CASE design repositories and large text
- databases. New machine architectures,
such as the AS/400, are inherently ob-
Jject-oriented systems.

There are many uses of the word "ob-
ject," but in most cases it encompasses
both properties (data) and behaviors

h (procedures). It is used loosely to de-
ij scribe the icons in a user interface, the

J entities in databases and the elements
manipulated by system software in
newer machines. In p: lan-
Buages, it refers to the encapsula!
units of properties and behaviors.

This week, Fl focus on object-oriented

interfaces and object-oriented pro-

Although "object-oriented" is used
freely to modify both interfaces and

grami

Object-oriented interfaces directly ben-
efit users. They are much easier for us-
ers to learn and work with than conven-
tional interfaces. One only has to com:
pare the user interface of the IBM PC

l written using an object-oriented pro-
ming language.

|
OOP Holds Promise of Simplifyying Computer Programming

with: that of the-Apple Macintosh to:see

the radical difference between the two
approaches.

The user interface to the PC is not in:
tuitive, and users reguire training to
deal with its alien command syntax. In
contrast, the object-oriented user inter-
face to the Macintosh can be learned
guickly and is easy to use.

An object-oriented user interface is
more appealing because it presents the
user with a view of the application that
is similar to the way humans deal with
the rest of their environment. People
handle physical objects at work, such as
books, pens and coffee cups, or more
business-related objects such as custom-

Understanding Object-Oriented Technology

j | :
"Objectoriented" describes a technology that's changing the.
Vay oemputers are programmed. It reguires a new way of.

thinking about the machine that is totally intuitive, (| !

dj if
lah SMEJE U
er files, orders and invoices. In a non!

a dispatch loop that responds to all user
actions. The user is in complete control
of the interface and might do anything.
The program must be ready to re- |
spond—redrawing windows, displaying
menus, calling application functions or
whatever action is appropriate.

The tool boxes for these interfaces
provide facilities for displaying the ob-
jects that make up the user interface,
such as windows, icons, pointers and
menus. They also provide the message
passing and gueues necessary to com-
municate between the interface and the
application. Typically the interface will
send messages to the application.

For example, the interface might send
a message to the application that the
mouse was clicked at a specific location.
The application then needs to determine
in what window, if any, the click oc-
curred, and how to respond. If the click

' was in a non-active window, then the
application must make the new window
active and redraw the screen appropri-
ately.

Higher-level interfaces to the tool box-
es are being provided, but at this point,
it still takes an experienced programmer
to work with them.

Managing Complex Code

' Object-oriented programming provides
major advantages to the programmer in
managing the complexity of a code. Us-
ing object-oriented technigues, program-
mers can more guickly develop applica-
tions that are easier to maintain, have
more reusable code and contain fewer
bugs.

University students working with ob-
ject-oriented languages reguire an initial
learning period to understand the new
technology and way of thinking about
programming, but then report vastly im-
proved productivity in writing pro-
grams. Vendors with large applications
and severe maintenance reguirements
are beginning to use object-oriented lan-
guages for development.

Just as a user deals with familiar ob-
jects in an object-oriented interface, the
developer writes code that defines and
manipulates objects in the programming
environment. The developer's objects
Can represent physical entities such as
inventory items, but can also represent
more abstract entities
such asa a Nk dispatcher or
collection.

Object-oriented programming allows
the programmer to encapsulate all of (
the code associated with an object, such
that the details of the implementation
of the object are completely hidden |

pops-up with the current customer in-
formation. Pointing to another icon or
menu item saves the new information
and closes the window.

This is a sharp contrast to character:
based interfaces to conventional applica-
tions. In traditional systems, the user
memorizes commands that must be is-
sued at the right time to get the desired
behavior from the system. The tradition-
al focus is on initiating commands and
operations first, and then selecting the
objects to be manipulated. This ap-
proach is the reverse of the way most
people manipulate objects in the real
world,

Programming environments that sup-

Objects are defined by
their propefties
and behatbtors.

Hiša " |
Port an object-oriented user interface, |
such as the Macintosh, IBM's Presenta- |

from the the rest of syste:
ori Maljščec and Microsoft Windows, ' Next seč I wil peka tečiai. ui
le the programmer with a rich col- rogramming |
I£etion o£ software tools to SI build Ze propan li more detail ai
ing the interface. The tools are designed To learn more about the subject of
to be called from Conventional program- these articles, please call The James
ni such as C and do not, re- Martin Report, an information service
Allre a knowledge of object.oriented updated guarterly, at (800) 242.1240, bi
stniki For information on nars,
da y ever, regulre a different. contact (in the United States and Can-
Programming, The style is best — ada) Technology Transfer [

called "event-dri
umre ven," and it is similar to

741 10th St, Santa Monica, Calif.
Unlike a pro. 90402 (2.3) 394-8305. In Europe, con-
$ram organized pipnanji ty doni: ma sm 2 New St., NEJA sa
cation of or- 9BX U:
£anization in an eventdriven program is (o524) 734 505. ea Kada