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Exam 3: The Relational Database Model

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Question 41

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The SELECT operator yields a vertical subset of a table.

A) True
B) False

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Question 42

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

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Question 43

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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 idea of determination is unique to the database environment.

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.

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.

Describe the use of null values in a database.

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.

_ 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

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

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

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

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

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.