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Customer Information Control System (CICS) is a Database/Data control system which is used in online applications from IBM. It manages its own memory space. CICS manages the sharing of resources, the integrity of data and prioritization of execution, with fast response. CICS authorizes users, allocates resources (real storage and cycles), and passes on database requests by the application to the appropriate database manager (such as DB2).

Mainframe is a big computing machine which handles thousands of users across the globe. Mainframe applications written in COBOL, CICS, FORTRAN, C, Java, PL/1 and more runs on this machine.

A CICS task basically a one-time execution of a certain CICS transaction. This process starts when the key is entered into the transaction, and the enter key is pressed. The execution process continues till the program returns the control back to CICS.

 IBM CICS Transaction Gateway is a connector for enterprise modernization of CICS assets.  It provides secure access to CICS from Java, Servlet,.Microsoft,NET Framework,C,C++ and COBOL applications etc. CICS Transaction Gateway for z/OS is part of the CICS family of products that includes; CICS Transaction Server, CICS Tools, CICS explore.

EIB (Execute Interface Block): One EIB is attached to each and every task and this stays with the task till its execution. CICS automatically provides some system-related information to each task in a form of EXEC Interface Block (EIB), which is unique to the CICS command level. We can use all the fields of EIB in our application programs right away.

By using, File Control Commands. Random, Sequential, forward and backward.

CICS basically deals with the execution as well as development of online applications. It establishes a communication channel through the terminal and facilitates the receiving as well as sending of data that is formatted. One of the primary aspects of CICS is the accessibility of database as well as the files that they contain.

• PPT –Program processing table
• PCT-Program Control table
• FCT-File Control table
• TST-Temporary Storage Table
• DCT-Destination Control Table
• RCT-Resource Control Table
• PLT-Program List Table
• SNT-Sign on Table

Program Processing Table – This basically consists of a list that has all the names of the programs in it along with maps. Furthermore, it tells us whether the version that is absolutely recent as available as a program in CICS or a fresh copy of the program is supposed to be loaded.

PCT (Program Control Table) is a complete list of transaction identifiers that are paired to respective corresponding programs.

FCT (File Control Table) is a complete list of all the files that have been used by CICS along with their status and record length.

DCT Stands for Destination Control Table. It is used to define TDQs.

The Program List Table records the set of applications programs that will be executed automatically at CICS start-up time.

Register security information of all programs.

The LOAD command retrieves an object program from disk and loads it into main storage – it’s primarily used for a constant table that will be available system-wide.

CEMT basically refers to Master Terminal Transaction. It happens to be an ID for system transaction and inquires about the status. Furthermore, it changes the status of the resources.

BMS stands for Basic Map Support. It allows you to code assembler level programs to define screens.

MDT stands for Modified Data Tag. If the modification of the field has to be done on the screen, then MDT acts as a bit of an attribute byte. MDT basically comes into play during an input operation.

COMMAREA is commonly termed as a communication area as it happens to be for temporary storage area. This is basically used as a passing medium for data amongst multiple programs that are loaded by a set of transactions or a particular transaction.

Transid basically stands for transaction identifier. In order to invoke a task of CICS, this character code consisting of four letters will be used.

Mapset is a collection of maps which are linked edited together to form a load module.It should have a PPT entry. It can have names from 1 to 7 chars.

AICA ABEND is just a Runaway Task that is executed at a later stage.

An attribute byte is basically used in CICS to define a particular transmission field or display. It basically contributes to the output field of the program.

For Skipper field, use ASKIP and for stopper field use PROT.

ENDBR Commend is used

By using GETMAIN

The CICS translator converts the EXEC CICS commands into call statements for a specific programming language.

To specify the paragraph or program label to which the control is to be passed if the “handle condition” occurs.

The DFHMDF macro defines fields, literal, and characteristics of a field.

Yes, It is used.

DSECT parameter is basically used in BMS in order to give shape to a symbolic map.

ENQ and DEQ are parts of task control commands that are used in making a resource serially recyclable.

There are Temporary data stores.

SEND MAP DATAONLY :Through this, the data is sent without the layout. It is used in order to refresh the data that comes to the screen.

SEND MAP MAPONLY :Through this, only the map is sent and not the data. Whenever we are in the process of sending menu screens, the data is never sent.

Pseudo-conversational will start a new task for each input. By coding a CICS RETURN command specifying ‘TRANSID (itself).

Conversational will have an active task during the duration of the data entry.

Multitasking is the feature supported by the operating system to execute more than one task simultaneously.

Multithreading is the system environment where the tasks are sharing the same programs load module under the multitasking environment. It is a subset of multitasking since it concerns tasks which use the same program.

DB2, DL/I, ORACLE

DFHEIBLK is Execute Interface Block. It is placed in the linkage section automatically by CICS translator program. It must be the first entry in linkage section. CICS places values prior to giving control to the program and we can find almost any information about our transaction.

Temporary storage is either main or auxiliary storage that allows the program to save data between task invocations.

An area used to transfer data between different programs or between subsequent executions of the same program. Needs to be defined in the Linkage Section.

The common systems area is the major CICS control block that contains system information, including pointers to most other CICS control blocks.  The CSA points to all members of STATIC storage.

A logical message is a single unit of output created by SEND TEXT or SEND MAP Commands.

An abnormal situation during execution of a CICS command is called an exceptional condition”. There are various ways  to  handle  these  exception  conditions:

Handle Condition Command: It is used to transfer control to the procedure label specified if   the exceptional   condition specified occurs.

Ignore Condition Command: It causes no action to be taken if the condition specified occurs in the program. That is control will be returned to the next instruction following the command which encountered the exceptional condition.

No Handle Option: This option can be specified in any CICS command and it will cause no action to be taken for any exceptional condition occurring during xecution of this command.

RESP Option: This option can   be specified in any CICS command. If the RESP option is specified in a command, CICS places a response code at a completion of the command.  The application program can check this code, then proceed to the next processing.

The following commands are available for the Program Control services:

LINK: To pass control to another program at the lower level, expecting to be returned.

XCTL: To pass control to another program at the same level, not expecting to be returned.

RETURN: To return to the next higher-level program or CICS.

LOAD: To load a program.

RELEASE: To release a program.

MASSINSERT is a WRITE option that modifies normal VSAM split processing, leaving free space after the inserted record, so subsequent records can be inserted without splits. It is ended by an UNLOCK command.

Temporary Storage Queqe (TSQ):

• Records in Temporary Storage can be read more than once.
• Records in TSQ can be read randomly.
• You may update an existing item in a TSQ.
• These names are dynamically defined in the application program.
• It cannot be accessed in batch.
• It cannot started automatically a CICS transaction.

Transient Data Queqe (TDQ):

• Temporary Data Queues can be read only once.
• Records in TDQ can be read only sequentially.
• A record in a TDQ cannot be updated.
• TDQs name must first be defined in the DCT (Destination Control Table).
• It may be used by batch application.
• It can start automatically a CICS transaction.

A program is considered reentrant if more than one task can execute the code without interfering with the other tasks execution.

 In CICS, you can handle errors using the HANDLE CONDITION command. When an error occurs, you can define a condition handler routine to execute specific error handling logic. The condition handler routine can perform actions such as displaying error messages, writing error logs, or initiating a recovery process.

 Data can be passed between CICS programs using COMMAREA (communication area). The COMMAREA is a common storage area defined in the Linkage Section of both the calling and called programs. The calling program stores data in the COMMAREA, and the called program accesses it using the same COMMAREA structure.

 CICS provides a feature called Resource Recovery (RRS) for atomic transaction processing. By defining a logical unit of work (LUW) using the START command, you can perform updates to multiple files within a single unit of work. If any update fails, all the updates are rolled back, ensuring data integrity.

 CICS provides record-level locking mechanisms to handle data conflicts. By using commands like ENQ and DEQ (Enqueue and Dequeue), you can acquire and release locks on data resources. This ensures that only one user can update a specific record at a time, preventing conflicts.

In CICS, you can use the ASKTIME command to retrieve the current time and calculate the elapsed time at specific points in the program. By displaying the elapsed time periodically, you can create a progress indicator to keep the user informed about the program’s progress.

 To access VSAM files in CICS, you need to define the VSAM files in the CICS system definition (CSD) file. The VSAM file definitions include information about the file organization, access methods, and file attributes. Once defined, the VSAM files can be accessed using appropriate CICS commands like READ, WRITE, and BROWSE.

 You can invoke a CICS program from a batch COBOL program using the EXEC CICS LINK command. The LINK command transfers control from the batch program to the CICS program. To pass data between the programs, you can use the COMMAREA or the CHANNEL communication methods.

In CICS, you can use the STARTBR command to initiate a browse operation on a VSAM file. By specifying a search argument, you can position the file cursor at the desired starting point. Then, you can use the READNEXT command to sequentially retrieve records that match the condition until the desired set of records is obtained.