Enterprise Applications and their Integration:

Based on operating systems and communication systems as a basic abstraction
layer, relational database management systems for storing and retrieving
large amounts of data, and graphical user interface systems, more and more
elaborate information systems could be engineered.
Most of these information systems host enterprise applications. These applications
support enterprises in managing their core assets, including customers,
personnel, products, and resources. Therefore, it is instructive to look
in more detail at enterprise information systems, starting from individual
enterprise applications and addressing the integration of multiple enterprise
applications. The integration of multiple enterprise applications has spawned
a new breed of middleware, enterprise application integration systems. Enterprise
application integration proves to be an important application area of
business process management.
These developments can be illustrated with an enterprise scenario. In the
early stages of enterprise computing, mainframe solutions were developed that
hosted monolithic applications, typically developed in assembler programming
language. These monolithic applications managed all tasks with a single huge
program, including the textual user interface, the application logic, and the
data. Data was mostly stored in files, and the applications accessed data files
through the operating system.
With the advent of database systems, an internal structuring of the system
was achieved: data was managed by a database management system. However,
the application code and the user interface code were not separated from each
other. The user interface provides the desired functionality through textual,
forms-based interfaces.
With lowering cost of computer hardware and growing requirements for
application functionality, more application systems were developed. It was
typical that an enterprise had one software system for human resources management,
one for purchase order management and one for production planning.
Each of these application systems hosted its local data, typically in a
database system, but sometimes even on the file system. In large enterprises,
in different departments, different application systems were sometimes used
to cope with the same issue.
What made things complicated was the fact that these application systems
hosted related data. This means that one logical data object, such as a
customer address, was stored in different data stores managed by different application
systems. Dependencies between data stored in multiple systems were
also represented by dedicated links, for instance through a contract identifier
or an employee identifier.
It is obvious that in these settings changes were hard to implement, because
there are multiple data dependencies between these disparate systems,
and changes in one system had to be mirrored by changes in other systems.
Detecting the systems affected and the particular change required in these
systems was complex and error-prone. As a result, any change of the data
objects, for instance, of a customer address, needed to be reflected in multiple
applications. This lack of integration led to inconsistent data and�in many
cases�to dissatisfied customers.