Introduction To Database Questions and Answers

Answer: B

Correct answer: False

Plenty of database applications are meant for a single user - a personal contact list, a small stock record, most Access databases. The multi-user case is the harder and more interesting one, but it is not the only one.

Answer: A

Correct answer: mn

A join is a selection applied to the Cartesian product, so it can never return more tuples than the product itself, which has \(m \times n\). That maximum is reached only when the join condition matches every pair - in effect a cross join. A typical equijoin on a foreign key returns far fewer.

Answer: A

Correct answer: Child

A weak entity has no key of its own and depends on an owner for its identity, so it is also called the child or subordinate entity; the entity it depends on is the owner, parent or dominant one. A loan payment identified only by its number within a given loan is the classic example.

Answer: B

Correct answer: Separate files

The database environment consists of users, applications, the DBMS, the database and the database administrator. Separate files are precisely what it replaces - the pre-database arrangement, in which each application kept its own file and the same data was duplicated and grew inconsistent.

Answer: D

Correct answer: All of the above.

A query language covers all three: ad hoc questions in near-English for end users; the data manipulation that application code is built on; and, through its data definition part, the structure of the database itself. SQL is the obvious example - SELECT, INSERT and CREATE TABLE all belong to it.

Answer: A

Correct answer: Structured Query Language

SQL is Structured Query Language. It came out of IBM’s System R project as SEQUEL and was standardised by ANSI in 1986; it covers not only queries but also data definition, updates and access control.

Answer: C

Correct answer: self-describing

A database stores metadata - the definitions of its own tables, columns, keys and indexes - alongside the user data, in system tables that can be queried like any other. That is what makes it self-describing, and it is why a tool can connect to an unfamiliar database and discover its structure without being told.

Answer: D

Correct answer: All of above

All three are among the reasons for using a DBMS: data independence, so storage can change without rewriting applications; centralised control, so standards, security and backup are managed in one place; and controlled redundancy, so the same fact is not stored in several places and allowed to drift out of step.

Answer: C

Correct answer: Data Structure

At bottom a database is a data structure - an organised arrangement of data with defined relationships - but a complex one, built from tables, indexes, keys and metadata, and large enough to need software of its own to manage it.

Answer: B

Correct answer: metadata

USER_TABLES describes the structure of the database - table names, column counts, keys - not the data the organisation stores. That is metadata, kept in the system catalogue and queryable with ordinary SQL, which is exactly what makes a database self-describing.