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

The ECI application programs make synchronous or asynchronous calls.
Synchronous calls return control when the called program completes; the
information returned is immediately available. Asynchronous calls return control
without reference to the completion of the called program, and the application is
notified when the information becomes available. Calls may be extended, that is
a single LUW may cover more than one successive call, although only one call
can be active for each LUW at a time. The application can manage multiple
LUWs concurrently if it uses asynchronous calls.
The called program can:
• Update resources on its own system
• Use DPL to call CICS programs on other systems.
• Access resources on other CICS systems with function shipping or DTP.
The ECI consists of three types of calls:
• Program link calls that cause a CICS program to be executed on a CICS
server.
• Status information calls that retrieve status information about the application
and its connection to the CICS server.
• Reply solicitation calls that retrieve information after asynchronous program
link or asynchronous status information calls.
Also available with the ECI is the ability to retrieve information about available
servers to which the calls are directed.
10.3.2 The External Presentation Interface
With the EPI, you can write applications that:
• Allow a non-CICS application program to be viewed as a 3270 terminal by a
CICS server system to which it is connected
• Connect to several servers at the same time
• Have several outstanding program calls at the same time
• Schedule transactions, where the application acts as the principal facility
• Balance sessions across the available CICS systems. See Chapter 8, “Using
CICS System Manager for AIX” on page 111.
In CICS servers that support access through the EPI, other CICS transactions
running in the server can use the START command to schedule transactions that
will use the non-CICS application as their principal facility. When a transaction
is initiated, 3270 data streams and events are passed between the CICS server
and the application. The application can present the contents of the terminal I/O
to its user in any manner appropriate to the application′s operating environment.
Transactions may be routed to other CICS systems by standard transaction
routing. Resources on other CICS systems can be accessed with function
shipping.
The EPI consists of functions, data structures, and events. The EPI functions
define application programming calls, such as installing new terminals to be
controlled by the process, sending data from a terminal, and terminating the
process. The EPI data structures define EPI data, such as reason codes, details
of events, terminal details, and sense codes. The EPI events are used to
respond to events that occur against a terminal, such as when a transaction
sends data and is expecting a reply.
Chapter 10. Application Design Considerations 147