Information Technology Reference
In-Depth Information
F
IG
. 10. Message-based programming model.
We consider the disadvantages of the message-based programming (compared
to
EJBSync
) to be considerable. Developers must “hand-craft” a two-part solution
(client and server) on a per-application basis. The application itself is responsible
for transactionally constructing and transmitting the message from the device to
the server, processing the message on the server, invoking the program that exe-
cutes the order on the server, and returning the results to the reconnected device.
EJBSync
is a step forward in the way it pushes more function into generic mid-
dleware.
EJBSync
also provides a productivity improvement, in that developers can
focus their efforts on the application-specific logic, rather than the infrastructure.
From the standpoint of productivity, as well, businesses would prefer to develop
only one version of an application, and deploy that application to both connected
and disconnected environments. The message-based approach usually requires that
two versions of an application must be developed: the
partitioned
version of the ap-
plication, described above, and a
connected
version, for machines which are always
connected to the server. Thus the partitioned version requires additional develop-
ment, test, and maintenance effort beyond that required for the standard connected
version. The message-based approach also requires extra programming to enable the
disconnected device to see locally-applied state changes—that is, state changes made
by the application to the cached database. This is because the straightforward imple-
mentation of the messaging approach does not actually make changes to the local
database; instead, the actions are saved for eventual transmission to the server. Ap-
plying the changes locally complicates the implementation because the changes must
be transactionally merged with the updated server state after the server has executed
the application messages.
