COM+, A Windows 2000 technology showcase
Microsoft introduced the first version of COM, the Component Object Model, with the release of Windows NT 3.51 in 1995. Designed as an
object-oriented, platform and tool independent infrastructure for component-based development, COM is the basis for virtually every technology that's
come out of Redmond in the past few years. While it doesn't get a lot of press, COM is the glue that binds together all of Microsoft's technology, from
its Unified Data Access (UDA) strategy to the future Windows DNA. Virtually every product out of Microsoft, including Office, SQL Server, and
innumerable others have their basis in COM. In 1996, Microsoft updated COM with DCOM, or Distributed COM, the version of COM that shipped
in Windows NT 4.0. And with the release of Windows 2000, Microsoft is ready to usher in a new era of component-based software development with COM+,
the most powerful version of COM ever created.
Think of COM+ as "the Windows 2000 version of COM." It's COM on steroids. COM mixed with the next version of
Microsoft Transaction Server (version 3.0). Or COM with a host of new services. The COM programming model, however you look at it, sounds the death
knell for monolithic desktop applications that have historically been created in straight "Petzold" C, MFC, or even Visual Basic. Because with
COM, location doesn't matter: COM enabled distributed applications whose components can be found on servers all over the world. It's literally a
software revolution.
Currently, most COM development extends the traditional client-server (or "two tier") programming model
to a three-tier (or multi-tier) model that consists of the following parts:
- Presentation layer: The user interface; the component that users interact with. This could be a traditional
"Win32" application or a Web application hosted in Internet Explorer.
- Business Rules layer: The components, typically located on a server, that handle the grunt work. Typically,
you will use this layer as an intermediary between the user and the data they are accessing on the back-end.
- Data layer: An enterprise data source such as SQL Server 7.0 or the Exchange message store. The user never
directly works with this layer, but rather accesses it through the middle, business rules, layer.
In typical Win32 applications, the presentation layer and business rules layer are almost always contained in the same
program (think of a standard Visual Basic desktop program). By further abstracting the distributed COM application into three or more layers, however,
we can use distinct tools, if desired, to create each layer. And, of course, each layer can run on a different machine, anywhere in the world.
So
|
|
