Information Technology Reference
In-Depth Information
that the deployed application will meet the business application requirements. Well-
known examples of such programming models include CORBA
[4]
,DCOM
[6]
, and
Enterprise JavaBeans (EJBs)
[10]
.
1 . 2
B u s i n e s s A p p l i c a t i o n s o n D i s c o n n e c t e d D e v i c e s
Business applications have traditionally been deployed in
connected
environments
in which the shared database can always be accessed by the application. In contrast,
when applications are deployed to mobile devices such as personal digital assistants
(PDAs), hand-held computers, and laptop computers, these devices are only inter-
mittently able to interact with the shared database. (In a client/server environment,
the shared database resides on the server.) Historically, resource constraints (e.g.,
memory and CPU) have precluded disconnected devices from running business ap-
plications. Ongoing technology trends, however, imply that such resource constraints
are disappearing. For example, DB2 Everyplace
[7]
(a relational database) and Web-
Sphere MQ Everyplace
[29]
(a secure and dependable messaging system) run on
a wide variety of platforms such as PocketPC™, PalmOS™, QNX™, and Linux;
they are also compatible with J2ME
[22]
configurations/profiles such as CDC and
Foundation. It seems likely that mobile devices will even be able to host middleware
such as an Enterprise JavaBeans container. As a result, business applications that
previously required the resources of an “always connected” desktop computer can
potentially run on a disconnected device.
Of course, there are non-business applications which do not have these require-
ments, but we argue that this set is declining in size and importance. For example,
even simple mobile applications typically support synchronization of updates back
to the user's personal PC. Since the PC copy of the database may be updated by
both the synchronization agent and other PC-based applications (e.g., calendaring),
the database is, in fact, shared. Also, users will probably be very disappointed to
discover that synchronization of updates did not occur transactionally (e.g., if con-
current updates to the same record were not detected and resolved in some way).
Finally, security of PDA databases is certainly a concern nowadays.
However, other issues, besides resource constraints, have precluded deployment
of business applications on disconnected devices. Fundamental algorithmic and in-
frastructure problems must also be solved. The algorithmic problems stem from the
fact that the application executes while disconnected from the server, but the work
performed must later be propagated to the server. To see why this is a problem,
consider the fact that business applications, by our definition, are structured as ap-
plication logic that reads from, and writes to, a transactional database that can be
concurrently accessed by other applications. Connected business applications have
