Tutorial:Software
Understanding
DNA And COM
We explain what COM, DCOM, COM+ and Windows DNA are, and what's involved
in writing and deploying applications which use them.
By Andrew Ward
M
icrosoft has adopted the um
with software developed using the cli
DNA Services
brella term Windows DNA
ent/server architecture.
(Distributed InterNet Archi
Much more important, however, is
Windows DNA Services can be cat
tecture) to embrace a range of tech
the need to be able to develop and
egorised in the following way:
nologies some old, some new which
change applications quickly, in re
together make up an architecture for
sponse to changing business needs.
G
Presentation Services (client inter
developing distributed applications
This is achieved by separating the pro
face).
on the Windows platform.
gram code responsible for the business
G
Application Services (component
Windows DNA fits into a multi tier
logic (policies and procedures) from
services or business logic).
world, and is aimed primarily at the
that which has to handle the interfaces
G
Data Services.
middle tier although Microsoft does
to the client, the back office services
G
System Services.
of course also provide technologies for
(such as database and legacy systems)
the client desktop and, in some cases,
and infrastructure services such as di
Presentation Services includes the
for the back office.
rectory and security.
native Win32 API as well as standards
From the development point of
Windows DNA encompasses serv
based presentation methods such as
view, DNA technologies take care of a
ices covering the full spectrum of ap
HTML, DHTML (Dynamic HTML),
significant amount of the necessary in
plication
needs,
from
client side
scripting and even COM components
frastructure that an application needs,
presentation services (via the Win32
themselves.
so that it is quicker and easier to de
API, for example) to back office data
Application Services represents the
velop new software.
services. Many of these services are
heart of Windows DNA, and provides
Applications written for Windows
available today, either included with
the primary infrastructure to support
DNA will run on Windows NT serv
the Windows desktop operating sys
COM objects (the term which usually
ers, but because parts of the DNA in
tems (and Windows NT 4 with the Op
refers to business logic components).
frastructure are also supported on
tion Pack), or provided by additional
Application Services include Microsoft
desktops under Windows 95, 98 and
applications such as SQL Server 7.0, but
Message Queue (MSMQ), Microsoft
Windows NT Workstation there is
some aren't due until Windows 2000.
Transaction Server (MTS) and COM.
tremendous flexibility. And, as a mid
Nevertheless, it is possible to de
Microsoft Internet Information Server
dle tier environment, Windows DNA
velop applications using Windows
(IIS) is usually treated as an application
must provide support for a range of
DNA technologies today using Visual
service. It provides the ability for active
client devices and communicate with a
Studio 6, and deploy them on Win
server pages (ASPs) to invoke COM
number of different back office re
dows NT 4.0 Server together with the
objects.
sources such as legacy systems and
Option Pack.
Data Services really means ADO
databases. As such, it is impossible to
draw a definitive diagram of what
DNA is, beyond the rather bland ge
neric picture shown in Figure 1.
COM is a CBD technology, and
therefore a competitor to Enterprise
Enterprise Trends
Windows DNA draws on a number
JavaBeans the Java world's answer to
of trends in the enterprise computing
arena. The most obvious is the desire
running server side software components.
for robust, distributed, scalable appli
cations, following bad experiences
Issue 107 (May 1999) page 15
File: T1510.1
PC Network Advisor
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