IMS DB Interview Questions (31 - 40)

31. What does SENSEG stand for?

SENSEG stands for Segment Sensitivity. It is a parameter used in the Program Specification Block (PSB) to define:

  • Access Permissions: Specifies which segments an application program is authorized to access.
  • Processing Options: Indicates the types of operations (such as read, insert, update, delete) that the program can perform on those segments.

32. What is a database record?

In IMS DB, a database record consists of a root segment and all of its dependent child segments. For example - 

School (root)  
└── Class (child)  
	└── Student (grand child)

Here, SCHOOL → CLASS → STUDENT is a database record.

33. What is a database key?

A database key is a unique identifier for a segment (like a primary key in SQL). It typically consists of key fields defined within the segment that uniquely identify each occurrence. For example - STUDENT-ID could be the key for the STUDENT segment.

34. What is a database buffer?

A database buffer is a portion of main memory where data from the database is temporarily stored before it's used by a program or written back to disk. It helps to:

  • Reduce disk I/O
  • Improve performance
  • Provide fast access to frequently used data

35. What is the role of the database buffer manager in IMS DB?

The Database Buffer Manager controls the use of database buffers. It:

  • Loads data into memory (buffer)
  • Keeps frequently used data in memory
  • Writes changes back to disk
  • Reuses buffer space efficiently

36. What is the syntax of a PCB mask in IMS DB?

In IMS DB, a Program Communication Block (PCB) mask is used in application programs to interface with the database. It defines the structure through which the program receives information from IMS, such as status codes and database positions. For example - 

01 PCB-NAME.  
   05 DBD-NAME         PIC X(8).  ← Database name  
   05 SEG-LEVEL        PIC XX.    ← Segment level  
   05 STATUS-CODE      PIC XX.    ← Success/error code  
   05 PROC-OPTIONS     PIC X(4).  ← PROCOPT (G, I, D, R)  
   05 KEY-FEEDBACK     PIC X(n).  ← Stores key info

37. What is the role of the Database Administrator (DBA) in IMS DB?

A Database Administrator (DBA) in IMS is responsible for:

  • Designing the database structure
  • Defining DBDs and PSBs
  • Running DBDGEN and PSBGEN
  • Monitoring performance
  • Performing backups and recovery
  • Managing security and access

38. What is a Transaction in IMS DB?

A transaction is a single unit of work (like withdrawing money from an ATM or booking a flight). In IMS, transactions are processed by IMS DC (Data Communications) and may update the database. For example - A bank "Transfer Money" transaction updates both sender and receiver accounts.

39. What is a database checkpoint?

A database checkpoint is a point in the sequence of transaction processing where all updates made to the database are committed and recorded. Checkpoints are crucial for:​

  • Ensuring Data Integrity: They confirm that all changes up to that point are saved.
  • Handles Recovery: In the event of a system failure, checkpoints allow IMS DB to restart processing from the last committed point, minimizing data loss.

40. What Does MPP Stand For?

MPP stands for Message Processing Program. An MPP is an application program designed to process incoming messages (transactions) in real-time. It handles online transactions (e.g., ATM withdrawals, flight bookings) and communicates with users via message queues.