SYSTEM CONCEPT - IBM Mainframe

The primary objective of CICS is to provide the control and service functions of the DB/DC system as a package. CICS is not a DB/DC system unless the applications accompany it, because CICS provides only the control environment for the DB/DC system. So CICS can be aptly called as a DB/DC control system. The CICS system concept is shown in the following figure. CICS forms a layer in between the application programs and the operating system and acts as an interface between the two. To achieve this, CICS has five major system components, each of which performs specialized services.

CICS System Concept

CICS System Concept

Data-Communication Functions

  • This component provides an interface between CICS and terminals or other systems.
  • It acts as an interface to telecommunication access methods like VTAM, TCAM, BTAM, etc.
  • It frees the application programs from terminal hardware through Basic Mapping Support (BMS), thus providing device and format independence.
  • It provides Multi Region Operation (MRO), through which more than one CICS region in a system can communicate.
  • Provides Inter System Communication (ISC), through which a CICS region in a system can communicate, with other CICS regions in other systems or other non-CICS systems.

Data-Handling Functions

  • Provides an interface between CICS and data.
  • Interfaces with data access methods such as VSAM and BDAM
  • Interfaces with database access methods like DB/2, SQL/DS and DL/I
  • Maintains data integrity by controlling simultaneous updates, providing data recovery facilities, etc.
  • Application Program Services
  • Provides the interface between CICS and application programs.
  • Interfaces with COBOL, PL/I and Assembler Programs.
  • Provides command level translation
  • Provides Execution Diagnostic Facility (EDF), Command Interpreter, (CECI), Screen Definition Facility (SDF), Trace and Dump facilities, etc.

System Services

  • Provides an interface between CICS and the operating system and carries out the functions like loading and releasing of application programs, acquiring and freeing of storage, task scheduling, etc. Monitoring Functions
  • Provides the functions for monitoring the various events within CICS and the necessary statistics for system fine-tuning.

Monitoring Functions

  • Provides the functions for monitoring the various events within CICS and the necessary statistics for system fine-tuning.

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