Introduction To Database Questions and Answers

Q: Conceptual design

Correct answer: Involves modelling independent of the DBMSConceptual design captures what the organisation needs to record - entities, attributes and relationships - without reference to any particular product. Choosing tables and types is logical design, and sizing and tuning belong to physical design; keeping them separate is what lets the same conceptual model be implemented on any DBMS.

Q: The relational database model was created by E.F. Codd.

Correct answer: TrueE. F. Codd, at IBM, set out the relational model in his 1970 paper “A Relational Model of Data for Large Shared Data Banks”. It replaced navigation through pointers with operations on sets of tuples, and every relational product since rests on it.

Q: One of the reasons why OODBMSs have not been widely used for business information systems is that OOP is obsolete.

Correct answer: FalseObject-oriented programming is anything but obsolete - it is the mainstream. OODBMSs failed to displace relational systems for business use for quite different reasons: the enormous investment already in relational databases, the maturity of SQL and its tools, and the fact that most business data fits the relational model perfectly well.

Q: An instance of relational schema R (A, B, C) has distinct values of A including NULL values. Which one of the following is true?

Correct answer: A is not a candidate keyA candidate key must satisfy two conditions: uniqueness and no NULLs. Distinct values alone are not enough - a NULL means the value is unknown, so it cannot be relied on to identify a row, and two NULLs cannot even be compared for equality. Since A contains NULLs it is neither a candidate key nor a primary key.

Q: A logical schema

Correct answer: Is the entire database.The logical (conceptual) schema is the complete description of the whole database - every table, column, key and constraint - as one community view. It is distinct from the internal schema, which says how the data sits on disk, and from the external schemas or subschemas, each of which shows one application its own slice.

Q: The purpose of a database is to help people stop using spreadsheets.

Correct answer: FalseThe purpose of a database is to keep track of things - particularly things with relationships among them, which a spreadsheet handles badly. Spreadsheets remain the right tool for calculation and analysis; the question is what kind of problem you have, not which tool to abolish.

Q: An application where only one user accesses the database at a given time is an example of a(n) ________ .

Correct answer: single-user database applicationBy definition: one user at a time means a single-user application - a personal address book or a small Access database. The distinction matters because concurrency control, locking and much of the administrative machinery exist only for the multi-user case.

Q: On which structure is the hierarchical model based?

Correct answer: TreeThe hierarchical model is based on the tree: one root, and every other record type with exactly one parent. Its successor, the network model, allows a record to have several parents and so is based on a graph.

Q: A database design may be based on existing data.

Correct answer: TrueA design may well start from data that already exists - spreadsheets, legacy files, another system’s tables. The process is different from designing from requirements: the existing structures have to be analysed and normalised rather than derived, and this is where much real database work begins.

Q: In E-R diagram generalization is represented by

Correct answer: TriangleGeneralisation and its inverse, specialisation, are drawn as a triangle labelled ISA, connecting the general entity set above to the specialised ones below. An ellipse is an attribute, a dashed ellipse a derived one, and a rectangle an entity set.

11.

Conceptual design

A.Is a documentation technique.
B.Needs data volume and processing frequencies to determine the size of the database.
C.Involves modelling independent of the DBMS
D.Is designing the relational model.

Answer: C

Correct answer: Involves modelling independent of the DBMS

Conceptual design captures what the organisation needs to record - entities, attributes and relationships - without reference to any particular product. Choosing tables and types is logical design, and sizing and tuning belong to physical design; keeping them separate is what lets the same conceptual model be implemented on any DBMS.

Discuss in Forum

12.

The relational database model was created by E.F. Codd.

A.True
B.False
C. None of the Above.
D.All of the Above.

Answer: A

Correct answer: True

E. F. Codd, at IBM, set out the relational model in his 1970 paper “A Relational Model of Data for Large Shared Data Banks”. It replaced navigation through pointers with operations on sets of tuples, and every relational product since rests on it.

Discuss in Forum

13.

One of the reasons why OODBMSs have not been widely used for business information systems is that OOP is obsolete.

A.True
B.False
C.None of the Above.
D.All of the Above.

Answer: B

Correct answer: False

Object-oriented programming is anything but obsolete - it is the mainstream. OODBMSs failed to displace relational systems for business use for quite different reasons: the enormous investment already in relational databases, the maturity of SQL and its tools, and the fact that most business data fits the relational model perfectly well.

Discuss in Forum

14.

An instance of relational schema R (A, B, C) has distinct values of A including NULL values. Which one of the following is true?

A.A is a candidate key
B.A is not a candidate key
C.A is a primary Key
D.Both (A) and (C)

Answer: B

Correct answer: A is not a candidate key

A candidate key must satisfy two conditions: uniqueness and no NULLs. Distinct values alone are not enough - a NULL means the value is unknown, so it cannot be relied on to identify a row, and two NULLs cannot even be compared for equality. Since A contains NULLs it is neither a candidate key nor a primary key.

Discuss in Forum

15.

A logical schema

A.Is the entire database.
B.describe data in terms of relational tables and columns, object-oriented classes, and XML tags.
C.Describes how data is actually stored on disk.
D.Both (A) and (C)

Answer: A

Correct answer: Is the entire database.

The logical (conceptual) schema is the complete description of the whole database - every table, column, key and constraint - as one community view. It is distinct from the internal schema, which says how the data sits on disk, and from the external schemas or subschemas, each of which shows one application its own slice.

Discuss in Forum

16.

The purpose of a database is to help people stop using spreadsheets.

A.True
B.False
C.None of the Above.
D.All of the Above.

Answer: B

Correct answer: False

The purpose of a database is to keep track of things - particularly things with relationships among them, which a spreadsheet handles badly. Spreadsheets remain the right tool for calculation and analysis; the question is what kind of problem you have, not which tool to abolish.

Discuss in Forum

17.

An application where only one user accesses the database at a given time is an example of a(n) ________ .

A.single-user database application
B.multiuser database application
C.e-commerce database application
D.data mining database application

Answer: A

Correct answer: single-user database application

By definition: one user at a time means a single-user application - a personal address book or a small Access database. The distinction matters because concurrency control, locking and much of the administrative machinery exist only for the multi-user case.

Discuss in Forum

18.

On which structure is the hierarchical model based?

A.Tree
B.Graph
C.Linked List
D.None of the above

Answer: A

Correct answer: Tree

The hierarchical model is based on the tree: one root, and every other record type with exactly one parent. Its successor, the network model, allows a record to have several parents and so is based on a graph.

Discuss in Forum

19.

A database design may be based on existing data.

A.True
B.False
C.None of the Above.
D.All of the Above.

Answer: A

Correct answer: True

A design may well start from data that already exists - spreadsheets, legacy files, another system’s tables. The process is different from designing from requirements: the existing structures have to be analysed and normalised rather than derived, and this is where much real database work begins.

Discuss in Forum

20.

In E-R diagram generalization is represented by

A.Ellipse
B.Dashed ellipse
C.Rectangle
D.Triangle

Answer: D

Correct answer: Triangle

Generalisation and its inverse, specialisation, are drawn as a triangle labelled ISA, connecting the general entity set above to the specialised ones below. An ellipse is an attribute, a dashed ellipse a derived one, and a rectangle an entity set.

Discuss in Forum

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