The research paper Component Object Model B Tech Seminar Topics for Computer Science describes what a Component Object Model is. It is suggested that COM is a specification or a set of rules provided such that language interop can be achieved. The objective of COM is that the code written in one language should be reused in the applications developed using other language. In order to specify a code as a component it is mandatory that the class definition has to inherit IUNKNOWN interface.
Methods in IUNKNOWN interface: The research paper identifies the following:
- QueryInterface à it is used to maintain the address of all the member functions defined in the class definitions in a VARRAY table structure.
- AddRef à It is used to increment the reference counter value by 1 whenever the application uses the definitions of the form component.
- Release à whenever the application which uses the COM component definitions is closed in a normal procedure then Release Method is used to release the reference counter information.
What COM Does: The research paper explains COM. It says that whenever a COM type application uses the definitions of the in process COM then a request will be given to the COM server where the component will be identified based on its GUID and processing of the component will take place at the PMA [ Private Memory Area ] of the OS and the request will be given back to the application. The paper also states the advantages and limitations of COM as follows:
- Advantages à The performance of the application will be very fast.
- Limitations à Always a IN process component depends on a application. The Component can’t be used independently.
The presentation concludes on a note suggesting that whenever the dot net application uses the definitions of the COM Component a request will be given to the CLR which uses the COM marshalling resource and identifies the application uses the definition of the COM Component and it defines a Runtime Callable Wrapper which sends a request to the Com Server where the Component is identified based on its GUID and the definitions of the COM component will be returned to the RCW and based on that definitions a relevant .net interop COM will be defined which will be used by the applications.
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