1. Explain the main control blocks available in IMS DB?

There are three control blocks (also known as DL/I control blocks)

► Database Description (DBD)
► Program Specification Block (PSB)
► Application Control Block (ACB)

2. Explain the advantages and disadvantages of a Hierarchical Database?

► Speed of access is faster because of the predefined data paths.

► Complex implementation
► Predefined tree structure reduces flexibility.
► Difficult to manage

3. Explain atomicity and aggregation?

Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.
A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.

4. Explain Phantom Deadlock?

In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.

5. What is IMS Software Environment?

IMS Software Environment consists of the below five main components:

► DL/I
► DL/I Control Blocks
► Application Programs

6. Explain the Hierarchical Database?

► Follows inverted tree structure
► Data relationship is predefined by it's structure
► Program accesses the data through predefined paths.

7. Explain a checkpoint and When does it occur?

A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.

8. What is a hierarchical database?

A hierarchical data base is a data model in which the data is organized into a tree-like structure. The structure allows repeating information using parent/child relationships: each parent can have many children but each child only has one parent

A hierarchical database is a database which formed with a root nodes and leaf nodes.An leaf node is the last node and each root node having at-least one node. this may not be the last node connected in a tree-like structure.

9. What is PCBs (Program communication blocks)?

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 (Program communication blocks).

10. What is DL/I?

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.

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