Introduction To Database Questions and Answers

Answer: B

Correct answer: Data elements in the database can be modified by changing the data dictionary.

The dictionary describes the data; it does not contain it. Editing the description does not change the stored values - changing an element means altering the data itself, through the DBMS. The other three statements are true: the DBA maintains it, it holds the name and description of every element, and it is primarily the DBA’s tool.

Answer: D

Correct answer: Not a value

NULL means that a value is missing, unknown or not applicable. It is emphatically not zero or a blank string, both of which are perfectly definite values. The consequence is that comparisons with NULL yield unknown rather than true or false, which is why x = NULL never matches and IS NULL must be used instead.

Answer: C

Correct answer: File Management System

Before database systems, applications kept their data in ordinary files, each written for one program. The resulting problems - the same data duplicated in several files, inconsistency between them, and applications that broke when a layout changed - are what the database approach was created to solve.

Answer: A

Correct answer: True

This is the correct chain: users → applications → DBMS → database. Every layer goes through the next, and only the DBMS touches the stored data - which is what allows security, integrity and concurrency to be enforced in one place.

Answer: A

Correct answer: Network Model

The record-based logical models are the relational, network and hierarchical ones - so called because the database is described as a collection of fixed-format records. The E-R model is an object-based (conceptual) model used for design, and the object-oriented model is object-based too.

Answer: C

Correct answer: e-commerce database application

A public shopping site is the standard example of an e-commerce database application: thousands of anonymous users browsing a catalogue and placing orders over the web. It is multi-user too, but e-commerce is the more specific description the question asks for.

Answer: A

Correct answer: True

A database holds both the data and the relationships among it - which orders belong to which customer, which items to which order. Storing the relationships is precisely what distinguishes a database from a collection of separate files or spreadsheets.

Answer: C

Correct answer: All the tuples of R1 and R2

Union returns every tuple that appears in either relation, with duplicates removed. It requires the two to be union-compatible: the same number of attributes, with matching domains. The last option describes an intersection or a join, not a union.

Answer: C

Correct answer: Doubly outlined rectangle

A double rectangle marks a weak entity set - one with no key of its own, whose identity depends on an owner entity. The relationship that connects it to its owner is drawn as a double diamond, and its partial key is underlined with a dashed line.

Answer: A

Correct answer: Database application and the database

The DBMS sits in the middle of the stack: user → database application → DBMS → database. The application never touches the stored data directly; it asks the DBMS, which handles the files, the indexes, concurrency and security. That indirection is what lets the physical storage change without rewriting every application.