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

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

Reasons For COM Distribution of library source code inefficient.Distribution of library source code inefficient. Dynamic Link LibrariesDynamic Link Libraries –alleviated source code difficulties. –Incompatible cross compiler support. Source code encapsulation, not binary encapsulation.Source code encapsulation, not binary encapsulation.

Primary COM Techniques Interface programming.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).

Primary COM Techniques The interface, IUnknown.The interface, IUnknown. –All interfaces must ultimately inherit from Iunknown. –Three methods QueryInterfaceQueryInterface AddRefAddRef ReleaseRelease

Primary COM Techniques Reference countingReference 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.

COM Topics Class objectsClass objects –Creates COM components ApartmentsApartments –Handle single and multithreading concerns ServersServers –Contains the binaries for the COM component.

COM Tools Microsoft’s native COM APIMicrosoft’s native COM API Microsoft Foundation Classes (MFC)Microsoft Foundation Classes (MFC) Microsoft’s Active Template Library (ATL)Microsoft’s Active Template Library (ATL)

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

Conclusion (cont) Successfully usedSuccessfully used –Windows operating systems –Microsoft applications for Windows –Third party developers writing for Windows OS Provides for fast, flexible, and reusable software componentsProvides for fast, flexible, and reusable software components

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