B2B Integration : A Practical Guide to Collaborative E-commerce

242 B2B Integration — A Practical Guide to Collaborative E-commerce
COM components can be written in any language, though Microsoft
makes it easier to create COM components using Microsoft development
languages, such as Visual Basic and Visual C++.
COM provides two types of servers to allow clients to invoke a
component: in-process and out-of-process. These COM servers provide
much of the same roles as an ORB.
In-process Server — An in-process server is a component where the
objects run inside the client's memory space. Essentially, the client has
a copy of the component on the local machine. In-process servers are
implemented using DLLs or EXEs. The components are invoked using
a local procedure call (LPC) (see Figure 8.9). LPCs are a means of
communication between different processes on the same machine. As
might be expected, in-process server components experience little
overhead and are very quick to execute.
Out-of-process Server — An out-of-process server runs in a separate
process or memory space, usually on a separate machine (see Figure 8.10).
They serve up 'remote' objects which are usually independent applications
in their own right. Out-of-process servers use RPC-like communication
similar to HOP with CORBA and RMI with J2EE. The
benefits of out-of-process servers include component reusability and
Client
Application
Vv_
Client
Application
DCE
RPC
Client Process
-1 r
Figure 8.9. — In-process server call
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CCM
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HI \
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RPC
-Vi
Remote Machine
Remote Server Process'
COM
Stub
Figure 8.10. — Out-of-process server call
Pemote Server
Remote
Object
vk