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this gives an introduction to microsoft dna.

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Java (Parts 1 and 2) in Slovak</A><BR>
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Introduction to Microsoft DNA
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COM - The Component Object Model
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<P>

COM is without doubt, the center of the Microsoft 
universe. Few Microsoft products are not built with it.

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What is COM? what is its purpose?

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COM was designed to solve a number of problems that 
have existed for sometime, not just in the Windows 
sphere but also within the development and application 
spheres.

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Code re-use is a nirvana that developers endure to achieve. 
However there have been very few situations where that could 
be realized. Take 
for instance an implementation of a solution in a C++ application. 
The developer builds generic classes to address a problem. 
From then on, the developer can re-use the code and can share 
it with others. While this looks good in theory, some problems 
arise in practice.

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First, the new code is language specific. So, if the second 
developer ONLY knew Visual Basic, the newly created C++ classes 
would be of no use.

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In COM, language independence is achieved.

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Encapsulation is also a target of the COM specification. 
If a developer builds an object that exposes some 
functionality and the new code becomes publicly consumed 
the interfaces exposed and used cannot subsequently change. 
If the exposed implementation details 
changed we could face the real prospect of causing a problem 
we had strived to avoid.

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By the nature of the COM specification objects provide 
methods to expose their implementation details and allow 
dynamic discovery. This enables such facilities as scripting 
languages to use such functionality without having to bind 
details in an early fashion. Coupling implementation details 
in such a fashion is called late binding. 

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One of the more important concepts of the COM model enables 
object implementations in the notion of location transparency. 
When an application calls an object's interfaces 
the application need not know whether the actual code is 
being executed locally or on a distributed machine. This 
location independence is provided through the use of proxy 
objects that sit between locations and marshals information 
between their instances. 

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Additionally, the COM specification includes implementation 
guidelines for transaction processing, distributed co-operation, 
and integrated security. Initially, COM implementations could 
only be targeted to Windows platforms (original COM was 
implemented as OLE - Object Linking and Embedding) however; 
other platforms are now supported by third party implementations

<P>

In the DNA methodology COM is a very important strand, 
involved in all the products and implemented directly, 
and natively, within the NT platform upon which the DNA 
technical implementation runs. However, DNA isn't COM 
alone, so we shall discuss where the other product fit 
and what they contribute.

<P>

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