Connie's Convenience Store - About Peter Coad

82 Connie’s Convenience Store Selecting System-Interaction Objects
Interaction within this system
A point-of-sale application is a very likely candidate for a client-server architecture.
However, do not build separate object models for the client and the server. Why? The
models will be exactly the same—almost. And that’s a waste of time and energy. Instead,
you are far better off building one object model.
You might encounter a variety of client-server environments, including:
– object environments on client and server, with object communications
support (ORB, SOM/DSOM, ODBMS)
– object environments on client and server, with nonobject communications
support
– object environment on the client but not the server.
If you find that you must deal with a transition to nonobject technology (which is
often the case), here’s the basic approach to follow:
– allocate objects to the client or server
– decide which services will be allowed to run on which platform
– add both client and server objects, for translating in and out of your object
technology.
If you have object-oriented environments on both client and server and your implementation
environment supports an ORB, or you are using an object-oriented database
that supports a client-server model, great news: you will not have to make any changes
to your model, except minor changes to match any specific requirements of the environment
you are using.
If you have object-oriented environments on both the client and the server, but there
is no object communications support between them, then you need to add a “server” object
for the client side, and a “client” object for the server side. These objects provide
the transitions across the non-object communications boundaries. You need to decide
which objects reside on each side of the boundary. You also need to define the client
and server objects, to provide a communications link, one that routes messages between
objects on different platforms.
If you have an object-oriented environment on the client and a relational database
on the server, then use DM objects to provide the mapping and boundary to the nonobject
oriented server.
Use an object-modeling tool with view management, working out what’s needed on
each processor.
For this point-of-sale application, you get to take it easy (after all, this chapter
needs to end at some point). Here’s what you have to work with:
– an object-oriented environment on both the client and server
– access to an object-oriented communications mechanism.
Piece of cake!
No client object is needed here. No server object is needed here.
Move ahead and establish responsibilities for authorization system.