e-business Application Solutions on OS/390 Using ... - IBM Redbooks

1.1.3 Transaction Services
Transactional processing has become the most important concept in enterprise
applications, and transaction services have become more important than ever in the
world of e-<strong>business</strong> applications.
In this world, a client request must be seen as a unit of work. Client requests must
either be 100 percent executed, or else rolled back. A two-phase commit protocol
is critical.
1.1.4 Messaging Services
The two most important benefits of messaging services are:
Asynchronous processing
Decoupling of systems
We discuss these benefits in detail in the following sections.
1.1.4.1 Asynchronous Processing
Asynchronous processing can be best compared to a situation where you would
have a telephone conversation. Imagine the world without answering devices, as
was the case some twenty years ago. You could only deliver your message by
phone to another person by having that person actually on the phone. Otherwise,
you would have to call that person again and again until he or she picks up the
phone.
By using an answering device on the other side, you could deliver the message
anyhow, even when the other person did not pick up the phone. You would not
have to call again and again.
This situation also applies to systems that communicate with each other. When the
sending system cannot reach the receiving system, you do not want to have the
sending system blocked because the receiving system is not available.
Using message services, the sending system will keep the message in a queue
until the receiving system is available again. It will then release the message.
Another feature of messaging services is that each message gets a unique
identifier, so that the receiving system can confirm back that the message has been
received.
1.1.4.2 Decoupling of Systems
Messaging services also decouple systems. Figure 2 on page 6 gives an example
of a messaging service where a client would communicate with a host system. The
client can also be on the same computer as the host system.
Chapter 1. The e-<strong>business</strong> <strong>Application</strong> Framework 5