CICS environment is a real time processing environment. CICS environment processes the data immediately using application programs logic.

CICS Transaction processing systems (TPS) provide users with timely, accurate and reliable access to data. TPS protect applications from data loss or corruption of data by performing below -

• Preserving data integrity by keeping track of updates and ensuring that they are committed in a reliable way across the whole network.
• Providing reliability by keeping shared disks up-to-date, backed up in case of damage, and fully accessible at all times.
• Allowing for flexibility in the distribution of data. Applications do not need to know where data is located; they make simple calls for data and servers determine where to find the data.

User data can be in the form of files, queues and database entries. A transaction processing system uses system data to control its operation. The most important difference for accessing data is that the data is stored in different formats called as structure.

The structure determines the application programming interface how easy or difficult it is to store and retrieve the data for a particular processing requirement. Structure makes accessing easy even the data is complex.

The structure is basically divided into two parts - physical structure and logical structure. physical structure describes about how the data stored and logical structure describes the layout of the data.

In some forms, the physical structure embedded with the logical structure used in application programs where in some forms it’s not. For example, DBMS physical structure not ties with logical structure used in application programs that are using it.

Files, queues the physical structure is embedded in application programs that are using it and the logical and physical structures coincide.

Files -

Files can be of fixed or variable length. Files can be entry sequenced (sequential), relative (relative) or clustered (indexed). Clustered (indexed) and sequenced (sequential) files offer a limited form of database function.

These file types are processed by servers and the server processing includes read from and write to user-defined files, gather statistics, acquire dynamic storage for I/O operations and manage the buffers and blocks used.

The main access method is the standard Virtual Storage Access Method (VSAM) which is used widely by transaction processing systems.

Queues -

Queues support the dynamic nature of transaction processing and offer flexibility in application construction. Queues provide scratchpad support, asynchronous communications between applications, transaction batching, general data storage and many other capabilities.

Databases -

Databases provides the greatest degree of data independence. They can be shared between CICS applications and other programs with equal freedom for both access and update and with full database integrity.

Applications can access databases either directly by embedding SQL calls within the application code or indirectly through interfaces to database managers.

Journals -

CICS supports journals which are special files used to record data needed to reconstruct events or changes to data. Automatic journaling can be used for files to write records to a specified journal if a record is read for update, a new record is added, or an existing record is deleted.