IMS Interview Questions and Answers

1/03/2010 No Comment

Mainframe IMS DB Interview Questions and Answers asked in IBM.

A very basic question, what is a Database and a DBMS?
Answer : A database is nothing but a collection of related data items organized in such a way that it can be processed by application programs. And a Database Management System is used to define and maintain the structure of the database.

Explain in brief what are the main objectives of a DBMS?

Answer : The main objectives of a database are listed below.
  • Increasing the data independence
  • Reducing the data redundancy
  • Providing indexing capabilities
  • Reducing the data maintenance
  • Providing data communication facilities
  • Providing data integrity and security

Explain about IMS (DB/DC).
Answer : IMS (Information Management System) is IBM’s hierarchical database management system. It has got two main components: IMS DB and IMS DC (also know as IMS TM) IMS DB - IMS/Database Manager as the name implies manages the IMS databases. It is used for physical storage creation and management and data retrieval. IMS DC / IMS TM - IMS/Data Communications or IMS/Transaction Manager handles online transaction processing system.

Explain in brief about DL/I?

Answer : DL/I is a command-level language to manipulate IMS databases. DL/I forms a bridge between application program and IMS database. It is used in batch and online programs to access data stored in IMS databases. Every access to an IMS database is through DL/I. The DL/I interface must be called to update or read a IMS database. DL/I allows both sequential and random processing of a database.

Name the five main components of a IMS Software Environment.

Answer : IMS Software Environment consists of the below five main components:
• IMS DB • DL/I • DL/I Control Blocks • IMS DC • Application Programs

Can you tell me what are the main control blocks available in IMS DB?

Answer : There are three control blocks (also known as DL/I control blocks) 
  • Database Description (DBD) 
  • Program Specification Block (PSB) 
  • Application Control Block (ACB)
What do you mean by DBD?
Answer : DBD (Database Definition) is used to define the physical structure of the database. One DBD for each database Created by a series of control statements – by a process called DBDGEN used by DL/I whenever database is used.

What do you mean by PSB?
What is Application Control Block?
Answer : PSB or Program Specification Block defines the programs view of the database and application programs access authority to database. It defines the logical data structure. A PSB is made up of one or more PCBs. Application Control Block is an internal control block consisting of combined information from the DBD and PSB.

Explain what you mean by a Hierarchical Database?
  • It follows inverted tree structure
  • Data relationship is predefined by it's structure
  • Program accesses the data through predefined paths.
List the advantages and disadvantages of a Hierarchical Database?
Answer : The main advantages of a hierarchical database is the Speed of accessing the data, the access is faster because of the predefined data paths.The disadvantages: are its Complex implementation, the Predefined tree structure that reduces a great extent and finally it is very difficult to manage the database.
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