DBMS Basics — Set 4

Correct Answer: D. E.F. Codd

Edgar F. Codd proposed the relational model in 1970 while working at IBM. His work revolutionized how data is stored and retrieved by introducing the concept of tables and keys. He also developed 12 rules for defining a true relational database.

Correct Answer: A. Recovery Manager

The recovery manager restores the database to a consistent state after a hardware or software failure. It uses logs to redo or undo transactions that were in progress. This ensures that the 'Durability' aspect of ACID properties is maintained.

Correct Answer: D. The overall design and structure of the database

The database schema is a blueprint that defines how the data is organized. It specifies tables, fields, relationships, and constraints. Unlike the data itself, the schema rarely changes once the database is established.

Correct Answer: C. ALTER

The ALTER TABLE command allows you to change the structure of a table without deleting it. It can be used to add, delete, or modify columns. This provides flexibility as business requirements evolve over time.

Correct Answer: A. Data redundancy and inconsistency

File systems often store the same data in multiple files, causing redundancy. This makes it difficult to ensure that all copies are updated simultaneously, leading to inconsistency. DBMS solves this by centralizing data management.

Correct Answer: D. To speed up data retrieval operations

An index is a data structure that allows the DBMS to find specific rows much faster. It works like the index at the back of a book to avoid scanning the entire database. However, creating too many indexes can slow down data insertion and updates.

Correct Answer: C. COUNT()

The COUNT() function returns the number of rows that match a specific criteria. It is very useful for generating statistics and reports from large datasets. You can count all rows using COUNT(*) or specific non-null values.

Correct Answer: D. A virtual table based on the result of a SQL query

A view acts as a virtual table that doesn't store data itself but shows data from one or more tables. It can be used to simplify complex queries or provide security by restricting access to certain columns. Views are updated automatically when the underlying table data changes.

Correct Answer: B. Network Model

The network model is a more flexible version of the hierarchical model where a child can have more than one parent. This creates a graph structure rather than a simple tree. It was standardized by the CODASYL group in the 1960s.

Correct Answer: C. Domain

A domain defines the data type and format that an attribute can hold. For example, a 'Gender' attribute might have a domain consisting of 'Male', 'Female', or 'Other'. It ensures that only valid data is entered into the database.