Physical Database Design Questions and Answers

Q: Which of the following are integrity controls that a DBMS may support?

Correct answer: All of the above.All three are integrity controls the DBMS itself can enforce: a default supplied when no value is given, a domain constraint limiting the permissible values, and a not-null constraint requiring one. Placing them in the database rather than in each application means every route to the data is checked identically.

Q: The three newest database architectures in use today are relational, multidimensional and hierarchical.

Correct answer: FalseThe hierarchical model is the oldest of the architectures, dating from the 1960s. The three newest in general use are relational, object-oriented and multidimensional. Including hierarchical among the newest inverts the chronology of the whole subject.

Q: A multidimensional database model is used most often in which of the following models?

Correct answer: Data warehouseThe multidimensional model organises data as measures indexed by dimensions - sales by product by region by month - which is exactly how analytical questions are asked. It suits the warehouse for that reason, and suits transaction processing badly, since it is designed to be read rather than updated.

Q: It is usually not very important to design the physical database to minimize the time required by users to interact with the information systems.

Correct answer: FalseResponse time as the user experiences it is very nearly the point of physical design. The logical design is already correct; what physical design adds is the indexing, organisation and placement that decide whether the system is usable, and user interaction time is the measure that matters most.

Q: Which of the following improves a query's processing time?

Correct answer: Use compatible data types.Comparing columns of different types forces the database to convert one of them, and a converted column generally cannot use its index - so a query that should have been an index lookup becomes a full scan. The other three options all add work: complexity, self-joins and subqueries each give the optimiser more to do rather than less.

Q: A bitmap index is an index on columns from two or more tables that come from the same domain of values

Correct answer: FalseAn index on columns from two or more tables drawn from the same domain is a join index, which exists to avoid computing the join at query time. A bitmap index is something else: one bit vector per distinct value, which is compact and fast where a column has few distinct values.

Q: Which of the following is an advantage of partitioning?

Correct answer: SecurityPartitioning lets the sensitive rows or columns be placed in their own partition with its own access controls, so a user reaching one part of a table need not be given the whole of it. The other three options are the recognised disadvantages - more complexity, uneven access speed, and extra space for the partitioning structures.

Q: In general, larger block sizes are used for online transaction processing applications and smaller block sizes are used for databases with a decision support or data warehousing system.

Correct answer: FalseThe sizes are the other way round. Transaction processing touches few rows at a time and benefits from small blocks, which reduce contention and wasted transfer. Warehousing scans large ranges, so large blocks bring more useful data per read. The statement has the two applications exchanged.

Q: Selecting a data type involves which of the following?

Correct answer: Improve data integrityChoosing a type that admits only the values the attribute can legitimately take is itself a constraint: a date column will not accept a non-date, and a numeric one will not accept text. The other options are the reverse of what is wanted - storage should be minimised, and a type admitting the widest range of values weakens the check.

Q: The primary goal of physical database design is data processing efficiency.

Correct answer: TruePhysical design begins from a logical design that is already correct, so what remains to be decided is how to make it perform: indexes, file organisation, clustering, partitioning and controlled denormalisation. Correctness is settled by then; efficiency is what physical design trades against.

31.

Which of the following are integrity controls that a DBMS may support?

A.Assume a default value in a field unless a user enters a value for that field.
B.Limit the set of permissible values that a field may assume.
C.Limit the use of null values in some fields.
D.All of the above.

Answer: D

Correct answer: All of the above.

All three are integrity controls the DBMS itself can enforce: a default supplied when no value is given, a domain constraint limiting the permissible values, and a not-null constraint requiring one. Placing them in the database rather than in each application means every route to the data is checked identically.

Discuss in Forum

32.

The three newest database architectures in use today are relational, multidimensional and hierarchical.

A.True
B.False

Answer: B

Correct answer: False

The hierarchical model is the oldest of the architectures, dating from the 1960s. The three newest in general use are relational, object-oriented and multidimensional. Including hierarchical among the newest inverts the chronology of the whole subject.

Discuss in Forum

33.

A multidimensional database model is used most often in which of the following models?

A.Data warehouse
B.Relational
C.Hierarchical
D.Network

Answer: A

Correct answer: Data warehouse

The multidimensional model organises data as measures indexed by dimensions - sales by product by region by month - which is exactly how analytical questions are asked. It suits the warehouse for that reason, and suits transaction processing badly, since it is designed to be read rather than updated.

Discuss in Forum

34.

It is usually not very important to design the physical database to minimize the time required by users to interact with the information systems.

A.True
B.False

Answer: B

Correct answer: False

Response time as the user experiences it is very nearly the point of physical design. The logical design is already correct; what physical design adds is the indexing, organisation and placement that decide whether the system is usable, and user interaction time is the measure that matters most.

Discuss in Forum

35.

Which of the following improves a query's processing time?

A.Write complex queries.
B.Combine a table with itself.
C.Query one query within another.
D.Use compatible data types.

Answer: D

Correct answer: Use compatible data types.

Comparing columns of different types forces the database to convert one of them, and a converted column generally cannot use its index - so a query that should have been an index lookup becomes a full scan. The other three options all add work: complexity, self-joins and subqueries each give the optimiser more to do rather than less.

Discuss in Forum

36.

A bitmap index is an index on columns from two or more tables that come from the same domain of values

A.True
B.False

Answer: B

Correct answer: False

An index on columns from two or more tables drawn from the same domain is a join index, which exists to avoid computing the join at query time. A bitmap index is something else: one bit vector per distinct value, which is compact and fast where a column has few distinct values.

Discuss in Forum

37.

Which of the following is an advantage of partitioning?

A.Complexity
B.Inconsistent access speed
C.Extra space
D.Security

Answer: D

Correct answer: Security

Partitioning lets the sensitive rows or columns be placed in their own partition with its own access controls, so a user reaching one part of a table need not be given the whole of it. The other three options are the recognised disadvantages - more complexity, uneven access speed, and extra space for the partitioning structures.

Discuss in Forum

38.

In general, larger block sizes are used for online transaction processing applications and smaller block sizes are used for databases with a decision support or data warehousing system.

A.True
B.False

Answer: B

Correct answer: False

The sizes are the other way round. Transaction processing touches few rows at a time and benefits from small blocks, which reduce contention and wasted transfer. Warehousing scans large ranges, so large blocks bring more useful data per read. The statement has the two applications exchanged.

Discuss in Forum

39.

Selecting a data type involves which of the following?

A.Maximize storage space
B.Represent most values
C.Improve data integrity
D.All of the above.

Answer: C

Correct answer: Improve data integrity

Choosing a type that admits only the values the attribute can legitimately take is itself a constraint: a date column will not accept a non-date, and a numeric one will not accept text. The other options are the reverse of what is wanted - storage should be minimised, and a type admitting the widest range of values weakens the check.

Discuss in Forum

40.

The primary goal of physical database design is data processing efficiency.

A.True
B.False

Answer: A

Correct answer: True

Physical design begins from a logical design that is already correct, so what remains to be decided is how to make it perform: indexes, file organisation, clustering, partitioning and controlled denormalisation. Correctness is settled by then; efficiency is what physical design trades against.

Discuss in Forum

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