Addressing OLTP Solutions with CICS: The Transaction Server ... - Ibm

Chapter 4. Using CICS Clients
4.1 Application Server Model
Users require an interface to interact with a CICS for AIX region. The
longer-established members of the CICS family, those running on mainframe
computers, were designed with a terminal network that largely consists of
3270-type displays and printers. Tens of thousands of CICS applications have
been written using the 3270 data stream for terminal input and output. The
existing investment in these CICS applications must be preserved and protected.
CICS for AIX and CICS Clients address this requirement and enable such CICS
applications to run successfully without any changes. The CICS Clients are
designed with modern requirements in mind, such as the ability to add a GUI to
a CICS Client or the ability to access a CICS for AIX region from a non-CICS
application.
CICS Clients support multiple functions, and multiple versions of CICS Clients
are available. By multiple functions we mean that the CICS client produced for
one operating system can provide a number of different interfaces, giving you
greater flexibility in the type of user interface that you decide to implement. By
multiple versions we mean that CICS Clients are available to run on multiple,
different hardware types and operating systems. This increased choice protects
the investment in the hardware and software that your users use.
The design of CICS Clients is such that the client accesses the business
application that runs in the server machine. Typically the client will run on a
different computer from the server so that processor usage is offloaded from the
server machine.
CICS Clients enable users to access CICS for AIX systems to run their business
applications. Through CICS Clients you can interact with the CICS for AIX
system as a terminal (3270-emulated terminal) user. CICS Clients also provide
additional functions that enable you to write your own user interface while still
providing client access to a CICS for AIX region. These functions are the ECI
and the EPI. The availability of the ECI and EPI greatly extends the choice when
deciding on a user interface. If none of the standard CICS-provided interfaces is
suitable, you can create your own and combine it with the ECI or EPI to provide
the CICS client component.
The design of CICS Clients is based on the application server model, a
processing model used in an open distributed multivendor OLTP environment.
The purpose of the model is to separate the presentation logic from the business
logic to enable the client to run on a separate processor from the business
application and so offload processor usage from the server machine.
Figure 13 on page 50 illustrates the components in the application server
model. In this model the screen handling is run on the end-user workstation, or
client computer. The business application is run in an application enabling
environment on a server computer located on the LAN. The application is
accessed through a thin layer of client code in the client computer.
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