IBM CICS (Customer Information Control System): A Guide to Mainframe Transaction Processing

This guide explores IBM's CICS (Customer Information Control System), a mainframe-based online transaction processing (OLTP) system. Learn about its primary functions, key components like the PPT (Processing Program Table), and understand its role in building high-throughput, reliable business applications for banking, order processing, and other enterprise tasks.

CICS Interview Questions and Answers

What is CICS?

Question 1: What is CICS?

CICS (Customer Information Control System) is an online transaction processing (OLTP) system from IBM. It's used for developing and running business applications on mainframes, facilitating the processing of transactions such as banking, order processing, and other business tasks that are performed online. It's designed for high-throughput, reliable transaction processing.

PPT (Processing Program Table)

Question 2: PPT (Processing Program Table)

The PPT (Processing Program Table) in CICS contains information about programs, including program name, mapset name, language, size, and storage location.

Primary CICS Function

Question 3: Primary Aspect of CICS

CICS is primarily used for building and managing online transaction processing (OLTP) applications. It offers efficient database access, terminal communication, and formatted data handling.

Integrated CICS Translator

Question 4: Integrated CICS Translator

The Integrated CICS translator is used for compiling programs containing embedded CICS commands. It interfaces with a COBOL or other language compiler to handle the CICS statements and generate the appropriate code.

CICS Job Priority

Question 5: CICS Job Priority

CICS itself is treated as a high-priority batch job by the underlying operating system.

Accessing Date and Time

Question 6: Getting Date and Time in CICS

The `ASKTIME` command retrieves the current date and time.

`CALL` vs. `LINK` in CICS

Question 7: `CALL` vs. `LINK` in CICS

Differences:

TCT and RCT

Question 8: TCT and RCT

In CICS:

• TCT (Terminal Control Table): Contains information about terminals connected to CICS.
• RCT (Resource Control Table): Contains information about DB2 resources.

Skipper and Stopper Fields

Question 9: Skipper and Stopper Fields

In CICS, `ASKIP` is often used as the attribute value for the Skipper field, and `PROT` for the Stopper field.

PCT and FCT

Question 10: PCT and FCT

In CICS:

• PCT (Program Control Table): Maps transactions to programs.
• FCT (File Control Table): Defines files accessible to CICS applications.

Releasing Records

Question 11: Releasing Records

The command `EXEC CICS UNLOCK RECORD ... END-EXEC` releases an exclusive lock on a record.

`START` vs. `XCTL`

Question 12: `START` vs. `XCTL`

Differences:

BMS (Basic Mapping Support) Options

Question 13: BMS Options

BMS options in CICS: Minimum, Standard, Full.

MDT Option

Question 14: Setting MDT Option

You can set the MDT (Map Data Table) option to 'ON' even without data entry using the FSET option in DFHMDF or dynamically in the program using the FIELD+A attribute.

CICS Tasks

Question 15: CICS Tasks

A CICS task is a unit of work initiated by a transaction. It runs until it completes and returns control to CICS.

`EXEC CICS HANDLE CONDITION`

Question 16: `EXEC CICS HANDLE CONDITION` Command

This command specifies how to handle conditions (errors) that may occur during program execution. It directs control to a specific paragraph or section of code to handle the error.

Important CICS Programs

Question 17: Important CICS Programs

Important CICS control programs:

• TCP (Terminal Control Program)
• KCP (Task Control Program)
• PCP (Program Control Program)
• FCP (File Control Program)
• SCP (Storage Control Program)

CEMT (CICS Execute Master Terminal)

Question 18: CEMT

CEMT is used for monitoring and managing CICS resources (transactions, tasks, files, programs).

BMS (Basic Mapping Support)

Question 19: BMS (Basic Mapping Support)

BMS is used to define and manage screen layouts (maps) in CICS applications.

CICS Control Programs

Question 20: CICS Control Programs

CICS control programs manage various aspects of CICS operations. These programs handle terminal communication, task management, program execution, file access, and storage allocation.

CICS Control Tables

Question 21: Important CICS Control Tables

Important tables:

• TCT (Terminal Control Table): Defines terminals connected to CICS.
• PCT (Program Control Table): Maps transactions to programs.
• PPT (Processing Program Table): Contains program information.
• FCT (File Control Table): Defines files.

Cursor Attributes

Question 30-32: Cursor Attributes

Cursor attributes provide information about the state and results of cursor operations:

• SQL%ROWCOUNT: Number of rows affected.
• SQL%FOUND: True if at least one row was fetched.
• SQL%NOTFOUND: True if no rows were fetched.
• %ISOPEN: Checks if the cursor is currently open.

PL/SQL Packages

Question 33: PL/SQL Packages

PL/SQL packages group related program units (procedures, functions, variables, cursors) into a logical unit, improving code organization and reusability.

Package Structure

Question 34: Parts of a PL/SQL Package

Two parts:

• Specification: Public interface (what's visible to other programs).
• Body: Implementation details.

Deleting a Package

Question 35: Deleting a PL/SQL Package

Use the `DROP PACKAGE` command to delete a package.

Executing Stored Procedures

Question 36: Executing Stored Procedures

Use the `EXECUTE` or `EXEC` command (or just call the procedure name directly).

Advantages of Stored Procedures

Question 37: Advantages of Stored Procedures

Benefits:

• Modularity
• Reusability
• Performance improvement (precompilation)
• Data security

Counting Table Rows

Question 34: Counting Table Rows

SELECT COUNT(*) FROM TAB;

Maximum Length of CHAR and VARCHAR

Question 35 & 36: Maximum Length of CHAR and VARCHAR

Maximum lengths in DB2:

• CHAR: 254 bytes
• VARCHAR: 4046 bytes

CICS Control Tables

Question 21: Important CICS Control Tables

CICS uses control tables to manage resources and configurations. Key tables:

• TCT (Terminal Control Table): Defines terminals connected to CICS.
• PCT (Program Control Table): Maps transactions to programs.
• PPT (Processing Program Table): Contains program information (storage location, size, etc.).
• FCT (File Control Table): Defines files used by CICS applications. Files used by CICS applications are listed here, and they are opened and closed by CICS itself.

COMMAREA (Communication Area)

Question 22: COMMAREA (Communication Area)

COMMAREA is a shared memory area used to pass data between CICS programs. It's a temporary storage location for data exchange within the same transaction. The maximum size of data that can be passed is 32KB.

EXEC Interface Block (EIB)

Question 23: EIB (EXEC Interface Block)

The EIB (EXEC Interface Block) is an area automatically loaded by CICS. It contains system information (like transaction ID, response code, timestamp) that you can access in your CICS programs.

CICS Transactions

Question 24: CICS Transactions

A CICS transaction is a unit of work initiated by a user request. Each transaction can execute a specific task. It's identified by a four-character code (Transaction ID or TRANSID) and typically involves interacting with CICS resources (like programs and files).

Task vs. Transaction

Question 25: Task vs. Transaction

A transaction can be invoked by multiple users; each user interaction creates a separate task.

`EXEC CICS RETURN` and TRANSID

Question 26: `EXEC CICS RETURN` with TRANSID

Including the `TRANSID` in the `EXEC CICS RETURN` command specifies the transaction to be executed when the user presses the attention key next.

CICS Programs

Question 27: Commonly Used CICS Programs

CICS control programs:

• Terminal Control Program (TCP)
• Task Control Program (KCP)
• Program Control Program (PCP)
• File Control Program (FCP)
• Storage Control Program (SCP)

EIBRCODE Field

Question 28: EIBRCODE Field

The `EIBRCODE` field in CICS's EIB (EXEC Interface Block) contains a response code indicating the success or failure of a CICS command.

Creating Maps with BMS (Basic Mapping Support)

Question 29: Creating Maps in CICS

BMS (Basic Mapping Support) in CICS helps to define screen layouts:

• DFHMDF: Defines individual fields on a map.
• DFHMDI: Defines a map.
• DFHMSD: Defines a mapset.

Transaction IDs (TRANSIDs)

Question 30: TRANSIDs

A TRANSID (Transaction ID) is a four-character code used to start a CICS transaction.

`EXEC CICS RECEIVE MAP`

Question 31: `INTO` vs. `SET` in `EXEC CICS RECEIVE MAP`

Differences:

• INTO: Copies map data into a specified storage area.
• SET: Returns the address of the map data area.

DFHMDF Attributes

Question 32: DFHMDF Attributes

Attributes defined using DFHMDF (for defining individual fields on a CICS map):

• POS (position)
• ATTRB (attributes)
• LENGTH
• INITIAL
• PICOUT
• GRPNAME
• OCCURS

EIB Block Fields

Question 33: Important EIB Fields

Important fields within the EIB (EXEC Interface Block):

• EIBCALEN (calendar date)
• EIBRESP (response code)
• EIBTASK (task number)
• EIBRCODE (return code)
• EIBTIME (time)
• EIBDATE (date)

Dynamic Calls in CICS

Question 34: Dynamic Calls

Dynamic calls in CICS allow for calling programs that are not known at compile time. This increases flexibility and allows you to build applications that adapt to changing environments or requests.

PF and PA Keys

Question 35: PF and PA Keys

Differences:

• PF (Program Function) key: Initiates data transmission on `RECEIVE MAP`.
• PA (Program Attention) key: Does not initiate data transmission.

MDT Option (Continued)

Question 36: Setting MDT Option (Continued)

Set the MDT (Map Data Table) option to 'ON' even without data entry by specifying `FSET` in `DFHMDF` or by setting it dynamically in your program.

Terminating Transactions

Question 37: Terminating Transactions

Use `EXEC CICS SYNCPOINT` to commit a transaction and release locks. Use `EXEC CICS RETURN TRANSID(transid)` to return to the user and specify a new transaction to run.

`SEND MAP` Commands

Question 38: `SEND MAP MAPONLY` vs. `SEND MAP DATAONLY`

Differences:

• SEND MAP MAPONLY: Sends only the map (layout); used for initial screen displays.
• SEND MAP DATAONLY: Sends only updated data; the screen layout is not re-sent.

CICS Service Transaction (CEDA)

Question 39: CEDA (CICS Execute Master Terminal)

CEDA is a CICS transaction used to access and manage various CICS control tables.

`XCTL` vs. `START`

Question 40: `XCTL` vs. `START`

Differences:

• XCTL: Transfers control to another program within the *same* task.
• START: Initiates a *new* task.

Mapsets

Question 42: Mapsets

A mapset in CICS is a collection of maps (screen layouts) that are loaded together as a single module.

`ENQ` and `DEQ`

Question 43: `ENQ` and `DEQ`

ENQ (Enqueue) and DEQ (Dequeue) are CICS commands used for resource control and synchronization. They allow multiple applications to coordinate access to shared resources, preventing data corruption and ensuring consistency. ENQ requests control of a resource, while DEQ releases that control.

What is CICS?

Question 1: What is CICS?

CICS (Customer Information Control System) is an IBM mainframe transaction processing monitor. It's used to build and run online business applications that handle large numbers of transactions concurrently.

PPT (Processing Program Table)

Question 2: PPT (Processing Program Table)

The PPT (Processing Program Table) in CICS contains information about programs and their associated resources (maps, files, etc.). This table is essential for program execution.

Primary CICS Function

Question 3: Primary Function of CICS

CICS's primary purpose is to handle online transactions. It provides efficient access to databases and files and manages communication with terminals.

Integrated CICS Translator

Question 4: Integrated CICS Translator

The Integrated CICS translator handles CICS commands embedded within application programs (e.g., COBOL programs). It generates the necessary code to interact with CICS during compilation.

CICS Job Priority

Question 5: CICS Job Priority

CICS transactions run with high priority in the operating system.

ASKTIME Command

Question 6: `ASKTIME` Command

The `ASKTIME` CICS command retrieves the current system date and time.

`CALL` vs. `LINK`

Question 7: `CALL` vs. `LINK` Commands

Differences:

TCT and RCT

Question 8: TCT and RCT

In CICS:

• TCT (Terminal Control Table): Defines characteristics of terminals connected to CICS.
• RCT (Resource Control Table): Defines DB2 resources available to CICS.

Skipper and Stopper Attributes

Question 9: Skipper and Stopper Attributes

The Skipper and Stopper fields are used in CICS map handling (often using `ASKIP` and `PROT` values respectively).

PCT and FCT

Question 10: PCT and FCT

In CICS:

• PCT (Program Control Table): Maps transactions to programs.
• FCT (File Control Table): Defines files used by CICS applications.

UNLOCK RECORD Command

Question 11: `UNLOCK RECORD` Command

The `EXEC CICS UNLOCK RECORD` command releases an exclusive lock on a database record.

`START` vs. `XCTL` Commands

Question 12: `START` vs. `XCTL` Commands

Differences:

BMS (Basic Mapping Support)

Question 13: BMS Options

BMS (Basic Mapping Support) options: Minimum, Standard, Full.

MDT Option

Question 14: Setting MDT Option

The MDT (Modified Data Tag) option in CICS indicates whether data in a map has been changed. You can set it using `FSET` in `DFHMDF` or dynamically in your program.

CICS Tasks

Question 15: CICS Tasks

A CICS task represents the execution of a transaction. Each user interaction creates a separate task.

`EXEC CICS HANDLE CONDITION`

Question 16: `EXEC CICS HANDLE CONDITION` Command

This command specifies the error-handling routine to be called if a specified condition occurs.

CICS Programs

Question 17: Important CICS Programs

Key CICS programs:

• TCP (Terminal Control Program)
• KCP (Task Control Program)
• PCP (Program Control Program)
• FCP (File Control Program)
• SCP (Storage Control Program)

CEMT (CICS Execute Master Terminal)

Question 18: CEMT

CEMT is a CICS transaction used for monitoring and controlling CICS resources.

BMS Maps

Question 19: BMS Maps

BMS (Basic Mapping Support) is used to define screen layouts (maps) for CICS applications. A mapset is a collection of maps.

ENQ and DEQ

Question 43: `ENQ` and `DEQ`

(This would require an explanation of `ENQ` (enqueue) and `DEQ` (dequeue) commands, which are used for resource synchronization in CICS.)

`XCTL` vs. `LINK`

Question 44: `EXEC CICS XCTL` vs. `EXEC CICS LINK`

Differences:

`NEWCOPY` in CICS

Question 45: `NEWCOPY` in CICS

The `NEWCOPY` option is used when a program needs a fresh copy of a map or data area, especially when dealing with multiple executions of the same program. This is often necessary to avoid data corruption or conflicts.

`OCCURS` in BMS Maps

Question 46: `OCCURS` in BMS Maps

The `OCCURS` clause in BMS is used to define repeating fields (arrays) within a map. This can simplify defining maps with multiple similar fields.

Terminal ID Registration

Question 47: Terminal ID Registration

Terminal IDs are registered in the Terminal Control Table (TCT).

CICS Code in Copybooks

Question 48: CICS Code in Copybooks

CICS commands can be included in copybooks, but recompilation is required when changes are made to the copybook.

Symbolic Map Storage

Question 49: Storage Determination in Symbolic Maps

For multiple maps, storage is determined by the size of the largest map. The largest map dictates the size of the storage area allocated.

CICS Translator

Question 50: CICS Translator

The CICS translator converts CICS commands into the equivalent statements in the host programming language.

`TRANSID` in `EXEC CICS RETURN`

Question 51: `TRANSID` in `EXEC CICS RETURN`

Including `TRANSID` in `EXEC CICS RETURN` specifies the next transaction to be invoked when the user presses an attention key.

Accessing VSAM Files

Question 52: Accessing VSAM Files Using Alternate Index

You access a VSAM (Virtual Storage Access Method) file using an alternate index by defining the appropriate access path in the File Control Table and using the File Control commands.

BMS Field Length of 0

Question 53: BMS Field Length of 0

A BMS field length of 0 means that no data was entered into the field.

`EXEC CICS HANDLE CONDITION` (Continued)

Question 54: `EXEC CICS HANDLE CONDITION` Command (Continued)

This command allows you to handle various CICS conditions (errors). It directs program flow to a specific handler routine if a condition occurs during execution.

AICA ABEND

Question 55: AICA ABEND

An AICA ABEND (abnormal end) in CICS usually indicates a runaway task (a task that has consumed excessive CPU time).

Uppercase Conversion

Question 56: Preventing Uppercase Conversion

Use the `ASIS` option with the `RECEIVE` command to prevent uppercase conversion of input data.

`INTO` vs. `SET` (Continued)

Question 57: `INTO` vs. `SET` (Continued)

Differences:

ESDS File Access

Question 58: Accessing ESDS Files

Yes, you can access ESDS (Entry Sequenced Data Set) files from within CICS.

`BUFFER` Option

Question 59: `BUFFER` Option in `RECEIVE`

The `BUFFER` option in the `RECEIVE` command retrieves the entire contents of the terminal's input buffer.

`ASKTIME` vs. `EIBTIME`

Question 60: `ASKTIME` vs. `EIBTIME`

Differences:

• ASKTIME: Gets the current time.
• EIBTIME: Gets the time the task started.

DFHMDF Macro

Question 61: DFHMDF Macro

The DFHMDF macro in BMS (Basic Mapping Support) defines individual fields on a CICS map.

MDT (Modified Data Tag), `FRSET`, and `FSET`

Question 62: MDT, `FRSET`, and `FSET`

The MDT (Modified Data Tag) indicates changes made to map fields. `FRSET` resets the MDT; `FSET` sets the MDT.

CICS Program Types

Question 63: CICS Program Types

CICS program types:

• Conversational
• Non-conversational
• Pseudo-conversational

Conversational Programs

Question 64: Conversational Programs

Conversational programs require user interaction; they alternate between sending data to the terminal and receiving input.

Non-Conversational Programs

Question 65: Non-Conversational Programs

Non-conversational programs run without user interaction; they typically generate reports or perform batch processing.

Pseudo-Conversational Programs

Question 66: Pseudo-Conversational Programs

Pseudo-conversational programs are event-driven; they respond to user actions but do not maintain continuous interaction.

TSQ vs. TDQ

Question 67: TSQ vs. TDQ

Differences:

ASRA ABEND

Question 68: Resolving ASRA ABEND

An ASRA ABEND (abnormal end) often indicates a runaway task. Troubleshooting involves examining task execution details using CICS monitoring tools.

DSECT Parameter in BMS

Question 69: DSECT Parameter in BMS

The DSECT (data section) parameter in BMS maps data areas to screen fields.

COMMAREA Size

Question 70: Default COMMAREA Size

The default size of COMMAREA (communication area) in CICS is 65K bytes.

CICS Error Handling

Question 71: Error Handling in CICS

Error handling in CICS involves checking return codes (`EIBRCODE`) and using `HANDLE CONDITION` to handle specific conditions.

CICS Error Codes

Question 72: AEIY Error Code

The AEIY abend code in CICS indicates a length error. This occurs when you attempt to move data to a field that is smaller than the source data. The receiving field is not large enough to accommodate the data being moved.