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Exam 4: Relational Model Characteristics

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Question 21

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A ____ key can be described as a superkey without unnecessary attributes, that is, a minimal superkey.

A) secondary
B) candidate
C) primary
D) foreign

E) A) and C)
F) C) and D)

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Question 22

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What are the characteristics of a relational table?

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1 A table is perceived as a two-dimensio...

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Question 23

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Codd's rule of ____________________ states that every value in a table is guaranteed to be accessible through a combination of table name, primary key value, and column name.

Referential ____ means that if the foreign key contains a value, that value refers to an existing valid tuple (row) in another relation.

The relational operators have the property of ____________________; that is, the use of relational algebra operators on existing relations (tables) produces new relations.

The equijoin takes its name from the comparison operator ____ used in the condition.

Each table in a relational database must have a primary key.

Depending on the sophistication of the application development software, nulls can create problems when functions such as COUNT, AVERAGE, and SUM are used.

In the relational model, ____________________ are important because they are used to ensure that each row in a table is uniquely identifiable.

Describe the use of nulls in a database.

In the relational model, ____ are important because they are used to ensure that each row in a table is uniquely identifiable.

If the attribute (B) is functionally dependent on a composite key (A) but not on any subset of that composite key, the attribute (B) is fully functionally dependent on (A).

Codd's Rule of ____ states: Application programs and ad hoc facilities are logically unaffected when changes are made to the table structures that preserve the original table values (changing order of columns or inserting columns) .

A ____ contains at least all of the attribute names and characteristics for each table in the system.

To avoid nulls, some designers use special codes, known as ____________________, to indicate the absence of some value.

____ combines all rows from two tables, excluding duplicate rows.

The DIVIDE operation uses one single-column table (e.g., column "a") as the divisor and one two-column table (e.g., columns "a" and "b") as the dividend.

A foreign key must exist in both tables that have a relationship.

The ____ relationship should be rare in any relational database design.

Proper data ____________________ design requires carefully defined and controlled data redundancies to function properly.