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COM - In plain English

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  • 02-11-2005 3:17pm
    #1
    mathie
    Registered Users Posts: 5,102 ✭✭✭


    Hi
    Can anyone tell me what COM is? And the differences with COM+ are?
    Also in this company I just joined they use ASP but they use COM too.
    Ive only ever used .asp files to connect to a database and that was fine.
    But why this COM layer? And whay a need for a registry (which they use)
    Thanks
    M


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    #2
    aidan_walsh
    Closed Accounts Posts: 17,208 ✭✭✭✭aidan_walsh


    http://en.wikipedia.org/wiki/Component_Object_Model


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    #3
    bonkey
    Registered Users Posts: 15,443 ✭✭✭✭bonkey


    mathie wrote:
    Hi
    Can anyone tell me what COM is? And the differences with COM+ are?
    Also in this company I just joined they use ASP but they use COM too.

    You've joined a company where COM is used, but you need to ask here what COM is? Can't you ask the developers in your company to explain it to you?
    But why this COM layer? And whay a need for a registry (which they use)
    Again, why not ask the developers why they use the design they use, rather than asking someone else why such a design might be used?

    jc


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    #4
    Evil Phil
    Registered Users Posts: 7,468 ✭✭✭Evil Phil


    mathie wrote:
    Hi
    Can anyone tell me what COM is? And the differences with COM+ are?
    Also in this company I just joined they use ASP but they use COM too.
    Ive only ever used .asp files to connect to a database and that was fine.
    But why this COM layer? And whay a need for a registry (which they use)
    Thanks
    M

    How did you use asp files to connect to the database? If you were using ADO or DAO (recordsets *hint hint*) then you've used COM already.

    The registry - Wikipedia, is there anything it can't do?


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    #5
    rsynnott
    Registered Users Posts: 4,003 ✭✭✭rsynnott


    Evil Phil wrote:
    The registry - Wikipedia, is there anything it can't do?

    Argh, set fire to it.


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    #6
    NutJob
    Closed Accounts Posts: 884 ✭✭✭NutJob


    Evil Phil wrote:
    How did you use asp files to connect to the database? If you were using ADO or DAO (recordsets *hint hint*) then you've used COM already.

    The registry - Wikipedia, is there anything it can't do?

    Am no it even make tea

    COM is litarlly the object model you use all the time in VB6 (prob going to get shot for over simplifieng here)

    It got replaced(ehm depreciated) in favour of the new fancy .Net Classes (they have some security due to bad press)


    As for the windows reg. Windows reg thats again just a replacement for the .ini files with extra restrictions. (shot again in the head this time)


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    #7
    rsynnott
    Registered Users Posts: 4,003 ✭✭✭rsynnott


    http://www.ddj.com/documents/s=1504/ddj0108vs/0108vs001.htm


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    #8
    Merrion
    Registered Users Posts: 1,421 ✭✭✭Merrion


    As we are in the mood to simplify:-

    COM is a way that a library (a dll or activeX control) can advertise what functions (classes and methods etc.) it supports and what parameters these methods need.

    COM+ does the same thing across a network connection...i.e. the library can reside on a different machine than the application calling it.

    COM uses the registry to store an unique number (in the format {999999999999-9999-9999-9999} ) which uniquely identifies one interface - it then uses the registry to find the library that implements this interface and the entry points of the functions to use.

    So if you write a program that uses a COM interface, the program goes to the registry and looks for the interface. If it finds it it then loads the dll into your program and looks after the rules about passing parameters to/from the library.


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    #9
    theexis
    Registered Users Posts: 131 ✭✭theexis


    Merrion wrote:
    COM+ does the same thing across a network connection...i.e. the library can reside on a different machine than the application calling it.

    Minor correction - COM over the network is basically DCOM. COM+ is a system supported mechanism for hosting applications and it provides powerful application middle tier functionality such as queuing, transactions, pooling and event subscription.

    COM+ should really be differentiated from COM since its more of a platform than an implementation standard - development with the COM+ platform is directly supported in .NET with the ServicedComponent class.


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