Introduction To Database Questions and Answers

Answer: B

Correct answer: Is much more data independence than some other database models

The relational model’s advantage is data independence: relationships are expressed by matching values in key columns, not by stored pointers, so tables can be reorganised or indexed differently without touching the applications. The older hierarchical and network models embedded the access path in the structure itself, which is what made them rigid.

Answer: D

Correct answer: Independent of both hardware and software

The conceptual model describes what data the organisation needs and how it is related, in terms of the business rather than of any machine or product. That independence is what lets the same model survive a change of hardware or a move to a different DBMS.

Answer: C

Correct answer: Database Management System

A DBMS is defined as a collection of interrelated data together with a set of programs to access it. The data alone is the database; adding the software that creates, queries and administers it gives the database management system.

Answer: C

Correct answer: View

A view is a stored query: it has no data of its own, and its rows are computed whenever it is referenced. Base tables and indexes both occupy real storage. (A materialised view is the exception that proves the rule - it is stored precisely because an ordinary view is not.)

Answer: C

Correct answer: The external view.

A subschema is the external view: what one particular application or user group sees. The logical view is the whole database as a single community picture, and the physical view is how it is actually stored.

Answer: D

Correct answer: R:base

R:base was the first PC product to implement true relational algebra. dBase-II, though far more widely used, was a file-oriented product without genuine relational operations - a distinction that mattered a great deal in the arguments of the mid-1980s.

Answer: A

Correct answer: SELECT

Select extracts rows that satisfy a condition - the horizontal slice. Project takes columns, join combines two relations on matching values, and product pairs every row with every row. (Confusingly, SQL’s SELECT statement performs projection as well; the relational operator named select is what the WHERE clause does.)

Answer: B

Correct answer: Self Join

A self join joins a table to itself, using two different aliases so that the two copies can be distinguished. It is how a table that refers to its own rows is unravelled - listing each employee beside their manager, where both are rows of the same employee table.

Answer: B

Correct answer: DB2

DB2 was IBM’s commercial relational product, descended from the System R research prototype built to test E. F. Codd’s 1970 relational model. IDMS implemented the older CODASYL network model, and dBase-II and R:base were PC products of the 1980s.

Answer: D

Correct answer: All of the above

A data dictionary holds the complete description of the data: the name, type and width of every field in every file, together with keys, indexes, constraints and often who may access what. It is metadata, and in a relational database it is itself queryable.