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COM & .NET Component Services by Juval Lowy

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Encapsulation via Interception in COM+

COM+ provides its component services via interception. You can configure your component to take advantage of services, and COM+ puts a proxy and stub between the component and its client, if the client and the component instance are incompatible with any one of the services. It also puts a proxy and stub between them if a service requires interception, regardless of the way the client and the object are configured. The exact object configuration is completely encapsulated by the proxy and stub and the call interception. Nothing in the client code couples it to the object configuration. This development is a major step toward ultimate encapsulation, in which the component contains almost nothing but business logic and in which the way it uses component services such as transactions, security, events, and activation is hidden from the client. Similarly, the component does not care about its client configuration, as the two do not need to interact with each other about the way they use the services.

Because an object can have the same threading model as its creating client while differing in other service configuration, apartments can no longer be the innermost execution scope of an object. Instead, COM+ subdivides apartments, so each object can be placed in a correct runtime environment appropriate to its needs and intercept all calls to the object. The subdivision of an apartment into units of objects that share the same configuration is called ...

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