COM: Microsoft's Component Object Model

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COM Microsoft's Component Object Model
Andrew C. Hopkins CSCI 397C-16 Object Oriented
Database Design and Management Professor Renee
Renner
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Introduction

• Microsofts Component Object Model (COM)
  provides a new methodology for software
  encapsulation, reuse, and versioning.
• Derived from Microsofts Object Linking and
  Embedding (OLE) technology.

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Reasons For COM

• Distribution of library source code inefficient.
• Dynamic Link Libraries
• alleviated source code difficulties.
• Incompatible cross compiler support.
• Source code encapsulation, not binary
  encapsulation.

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Primary COM Techniques

• Interface programming.
• Supports binary layout and compatibility.
• Contains pure virtual functions and no members.
• Inherits from a single ancestor class.
• Sets the Virtual Table (VTBL).

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Primary COM Techniques

• The interface, IUnknown.
• All interfaces must ultimately inherit from
  Iunknown.
• Three methods
• QueryInterface
• AddRef
• Release

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Primary COM Techniques

• Reference counting
• AddRef increments the interior count.
• Release decrements the interior count.
• Object releases itself from memory when reference
  count is 0.
• Maybe per interface or per COM object.

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COM Topics

• Class objects
• Creates COM components
• Apartments
• Handle single and multithreading concerns
• Servers
• Contains the binaries for the COM component.

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COM Tools

• Microsofts native COM API
• Microsoft Foundation Classes (MFC)
• Microsofts Active Template Library (ATL)

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Conclusion

• Many more COM topics and techniques.
• Interface Definition Language (IDL)
• Categories
• Automation
• Distributed COM (DCOM)

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Conclusion (cont)

• Successfully used
• Windows operating systems
• Microsoft applications for Windows
• Third party developers writing for Windows OS
• Provides for fast, flexible, and reusable
  software components

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Works Cited

• Box, Don, Essential COM, Addison-Wesley
  Publishing Company, Reading, Massachusetts, 1998.
• Denning, Adam, ActiveX Controls Inside Out,
  Second Edition, Microsoft Press, Redmond,
  Washington, 1997.
• Rogerson, Dale, Inside COM, Microsoft Press,
  Redmond, Washington, 1997.