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Chapter 23. REXX/CICS High-level Client/Server Support
Client/Server computing has become very popular in the Information Processing industry. Some of the
advantages of client/server computing are:
v The ability to effectively integrate the strengths of mainframes, mini-computers, and new cost-effective
workstations, in a transparent fashion.
v The ability to incrementally scale the size of computer's systems, up or down (right-sizing).
v The simplification of complex application systems by breaking them down into manageable sets of
clients and servers.
v Applications and data can be distributed throughout a network for better performance, integrity or
security.
v The ability for enterprise-wide access to data and applications, wherever they reside in the network,
from a variety of unlike computer systems or workstations.
Overview
REXX/CICS introduces REXX language Client/Server support. REXX/CICS provides a high-level
client/server capability. This capability includes:
v High-level, natural, transparent REXX client interface
v Support for REXX-based application clients and servers.
High-level, Natural, Transparent REXX Client Interface
REXX/CICS supports a high-level easy to use interface from client REXX execs to application servers
through the ADDRESS keyword instruction in REXX. The ADDRESS instruction includes an external
environment name that is used to determine the name of the external procedure that is called to process
subsequent REXX command strings.
REXX/CICS provides the optional ability for the environment name (specified in the ADDRESS instruction)
to be the name of an application server. This capability is provided by the REXX/CICS DEFCMD and
DEFSCMD commands.
The DEFCMD command provides the ability to define (or redefine) REXX commands and environments,
and it provides the ability to specify whether an environment-command combination is to be handled by a
traditional CALLed routine or by an REXX application server.
Support for REXX-based Application Clients and Servers
In addition to the above REXX client interface, several facilities provide support for the use of application
servers written in REXX. One of these facilities is the WAITREQ command, which is used by servers to
wait for requests from clients. Another facility, the C2S and S2C commands, provide the ability for servers
to fetch or set the contents of client variables. Another capability, Automatic Server Initiation (ASI) provides
for servers to be started automatically when a request arrives from a client.
Value of REXX in Client/Server Computing
Some advantages of using REXX for implementing client/server solutions are:
v The availability of REXX interpreter support under REXX/CICS with its quick development cycle and
excellent source-based interactive debugging allows the rapid prototyping and development of complex
systems.
v The high-level client/server interfaces in REXX/CICS can improve development productivity and lower
maintenance costs
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