In a CICS application, which commands are used to read a VSAM KSDS file sequentially in ascending key order during a browse operation?

Introduction / Context:
CICS provides specific file control commands to work with VSAM datasets, including Key Sequenced Data Sets (KSDS). When reading a KSDS sequentially in ascending key order, you typically perform a browse operation. Interview questions about this topic check whether you know the correct sequence of CICS commands for starting, continuing, and ending such a browse.

Given Data / Assumptions:

• We have a VSAM KSDS defined to CICS as a file resource.
• We want to read records sequentially in ascending order by key.
• We are writing a CICS application program using EXEC CICS file control commands.

Concept / Approach:
To read a VSAM KSDS sequentially, CICS uses the concept of browsing. You begin a browse with STARTBR (Start Browse) to establish the starting position based on a key or key range. After that, you use READNEXT repeatedly to move forward through the file in ascending key order, retrieving one record at a time. When the browse is complete, you issue ENDBR to end the browse and release any associated resources. READNEXT is specifically designed for sequential forward browsing in conjunction with STARTBR.

Step-by-Step Solution:
Step 1: Define the VSAM KSDS file in the CICS region and ensure it is properly open and available to the application. Step 2: In the program, issue EXEC CICS STARTBR FILE(file-name) KEY(key-value) or an equivalent, which positions the browse at the specified key or the next higher key if an exact match is not found. Step 3: After STARTBR succeeds, issue EXEC CICS READNEXT FILE(file-name) into a record area to retrieve the first record at or after the starting key. Step 4: Repeatedly execute READNEXT in a loop to step through subsequent records in ascending key order until an end of file condition is reached. Step 5: When the browse is complete or no more records are needed, issue EXEC CICS ENDBR FILE(file-name) to terminate the browse operation cleanly.

Verification / Alternative check:
You can verify correct behaviour by running the program against a KSDS with known keys and checking that the records are returned in strictly increasing key order. Program traces and CICS monitoring tools will show a STARTBR followed by a series of READNEXT calls. Attempting to use READNEXT without a prior STARTBR will typically result in an error, confirming that a browse must be initiated before sequential reading. Documentation for CICS file control also emphasises the STARTBR, READNEXT, and ENDBR sequence for forward browsing.

Why Other Options Are Wrong:
Option B is incorrect because READ UPDATE is used for random access and updating records, not for establishing a sequential browse. Option C is wrong because WRITEQ TS writes data to temporary storage queues and has nothing to do with reading VSAM KSDS files. Option D is incorrect because ENDBR ends an existing browse; it cannot start one, and READPREV is used for backward browsing rather than forward sequential reading.

Common Pitfalls:
Common pitfalls include forgetting to issue ENDBR and leaving browses open, which can tie up resources, or using incorrect keys with STARTBR that cause browses to start at the wrong position. Another issue is confusing READNEXT with READ, which can lead to unintended random access patterns. Properly using STARTBR, READNEXT, and ENDBR ensures predictable and efficient sequential processing of KSDS records in CICS applications.

Final Answer:
To read a VSAM KSDS sequentially in ascending order, you issue STARTBR to begin the browse at a starting key and then use READNEXT repeatedly to retrieve records forward in key sequence, ending with ENDBR when finished.