VB Forum / COM / September 2008

You might be confusing COM+'s use of the term "Application" with the common
use of the term - that of a single .exe or program. Also the terms
"application" and "service" are not exclusive, ie, there is a "Service
Application" or a "Library Application".

In COM+ the main unit is called an "Application". It is a set of
adminstrative information/data about components that work together. In the
older MTS this data was called a 'package'. (A term I liked better, but MS
change it with COM+) So think of COM+'s 'Application' as a 'Package'. A COM+
Application then isn't just a single .exe, it includes ALL the elements
needed to do a job - registry, components, type libraries, etc.

Note: all COM+ components are DLLs.

A "COM+ Service Application" runs in a separate address space than then
client. Either on the same box or remotely. This is similar to what an
ActiveX .EXE would be in COM.

A "COM+ Library Application" runs in the same address space as the client.
Similar to how we would use an ActiveX DLL.

So whether Service or Library is purely a design-time decision. You may
write different code for components that are to operate in one or the other
environment, but often not. The difference is what your component is doing
and how COM+ handles the infrastructure to produce the desired effect.

For example, if a component is going to be used within a Service
Application, then COM+ needs to setup a proxy for the client and an
interceptor (dllhost) in the component's address space and create a RPC
Channel for them to communicate. If in a Library Application, the COM+ will
create a Intercetor in the client's space.

Warning: overly simplified. But that's why you have to categorize your
packaged 'application' when you configure COM+.

hth
-ralph