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Exam 3: The Relational Database Model

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Question 41

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The row's range of permissible values is known as its domain.

A) True
B) False

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Question 42

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A key can be described as a minimal superkey,a superkey without any unnecessary attributes.

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

E) A) and B)
F) None of the above

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Question 43

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

According to Codd's rule of relational database,"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) ."

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

The practical significance of taking the logical view of a database is that it serves as a reminder of the simple file concept of data storage.

The idea of determination is unique to the database environment.

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

_ are especially useful when you are trying to determine what values in related tables cause referential integrity problems. a.Inner joins b.Outer joins b.Theta joins d.Equijoins

A null is created when you press the Enter key or the Tab key to move to the next entry without making a prior entry of any kind.

The SELECT operator yields a vertical subset of a table.

If one department chair-a professor-can chair only one department,and one department can have only one department chair.The entities PROFESSOR and DEPARTMENT exhibit a(n)relationship.

A primary key is a(n)key chosen to be the primary means by which rows of a table are uniquely identified.

Describe the use of null values in a database.