COM & .NET Component Services

Applications, DLLs, and Components

COM+ applications are logical packaging units; DLLs, however, are physical packaging units. There is no correlation between logical and physical packaging. The only requirement is that a configured component must belong to exactly one COM+ application; it cannot belong to more than one, and it must belong to at least one to take advantage of COM+ component services. As demonstrated in Figure 1-8, a COM+ application can host components from one or multiple DLLs (Application 2 has components from two DLLs). It is also possible that not all the components in a DLL are hosted in COM+ applications (such as component E), and one DLL can contribute components to multiple COM+ applications (DLL 1 contributes components to Application 1 and Application 2).

Figure 1-8. COM+ applications and DLLs

The separation of physical from logical packaging gives you great flexibility in designing your application’s layout. All the components in the same COM+ application share the same application-level configuration settings, regardless of their underlying DLL packaging. However, I recommend that you avoid installing components from the same DLL into more than one application, such as components B and C in Figure 1-8. The reason is that components in the same application are assumed to operate tightly together and trust each other. On the other hand, nothing is assumed ...