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Overview of the SAS/C and CICS Environments

CICS Background

The use of online systems is common today. However, in the past, developing an online system required customized programming involving calls to the operating system, telecommunication access methods, and data access methods, in addition to application program development.

To free the programmer from concerns about hardware and other components outside the realm of the application itself, Database/Data Communication (DB/DC) control systems were developed. In the late 1960s, CICS was introduced by IBM as one such DB/DC control system. CICS is considered a control system for DB/DC because it provides the control environment for a DB/DC application. That is, an application program that uses databases and data communications in a real-time manner can work with CICS to form a complete DB/DC system.

CICS has evolved from a macro-based DB/DC system to a high-level, command-based language. Early versions of CICS required the programmer to use macros whenever system services were required. Presently, CICS is command-based: one CICS command now accomplishes what used to require a series of macro-based calls. Coding CICS commands in application programs makes requesting CICS services much easier than using earlier macro-based versions. These commands are coded in your SAS/C program using the following general format:

EXEC CICS <command>

The details of coding commands are discussed in The SAS/C CICS Command Translator.

As noted earlier, coding CICS commands means that you are requesting CICS services to handle various details of operating system tasks, such as communicating with terminals and storage management. The following components of CICS provide such services to your application program:

These functions are described in more detail in the following sections. The relationship between the operating system, CICS, and your application programs is illustrated in SAS/C CICS Environment.

SAS/C CICS Environment

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Data-Communication Functions

The CICS services for data communication provide communication interfaces. Communication interfaces can be between other systems and CICS or between terminals and CICS. Data-communication functions include the provision of Basic Mapping Support (BMS), which frees the application program from concerns with specifics of devices and formats when you are working with displays. Considerations for Basic Mapping Support are discussed in Terminal Control and Basic Mapping Support.

Data-Handling Functions

This component of CICS provides an interface between CICS and the data needed by your application program, including interfaces with data access methods, such as VSAM, and interfaces with database access methods, such as DL/I. Also, provisions are made for assuring data protection and integrity. Aspects of file handling that are pertinent to your application programs are covered in Handling Files.

Application Program Services

CICS provides an interface with your program through screen definitions, command interpretation (CECI), debugging facilities, and so forth. These services are described in Using C for CICS Application Programs.

System Services and Monitoring Functions

The system-service component of CICS provides an interface with the operating system. Functions are provided for program, storage, and task control. Topics related to system services are included in Using C for CICS Application Programs.

Monitoring functions are provided in the CICS environment for system tuning and performance considerations. Running and Debugging SAS/C Programs in the CICS Environment suggests ways of improving performance using C. Refer to the CICS documentation appropriate for your site for additional details.


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