Modeling for System Integration
5.1 Terminology of System Integration
Communication between IT systems occurs through interfaces. Therefore, an interface is
the basic element of system integration. Through an interface, an IT system (the sender)
sends information to another IT system (the receiver). A particular IT system can be both
a sender and a receiver.
messagesIT systems that are connected via interfaces exchange . A message is sent by
the sender IT system, with the expectation that receiving the message—immediately or
later—initiates an activity in the receiver IT system. For the receiver IT system, each
message received constitutes an event to which it responds.
For instance, if an invoice is sent in an electronic format, this event is an
invoice receipt
for the receiver of the invoice. After the receipt of the invoice, the receiver has a certain
time frame to pay the bill. The receiver IT system has to confirm the receipt of the
invoice and possibly activate another IT system, for example, an accounting system that
records the balance.
Messages can be loaded with additional information that is necessary to process the
activities of the receiver system. Generally, this information is structured data with
defined semantics, such as invoice data or a passenger list. In UN/EDIFACT, for
instance, this information is called
reference data.
Furthermore, messages have assigned control and routing information, for example,
sender address, receiver address, meta-information about the content of the message, or
checksums. We can also describe this information as the 'packaging' of a message.
There are various alternatives to transform these three components: event, information,
and control and reference data, into a message that can be exchanged between IT
systems. Control information can, for instance, be 'hidden' in interface programs, or can
be sent as additional data. An event can be a program call, or it can be transferred in a file
that contains further message data.
In UN/EDIFACT messages, which are also referred to as business documents, all three
components are contained in one single transfer unit (mainly data): event (message type),
information (reference data), and control information (service segments).
Messages that are sent in XML format are also called documents in XML. They contain
at least reference data and meta-information. A great advantage of XML compared to
UN/EDIFACT is that each XML message carries with it a reference to its structural
description. This has the advantage that everyone can read the XML message.

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