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Exam 3: The Relational Database Model

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Question 1

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The following example exhibits ____________________ integrity: The CUSTOMER table's primary key is CUS_CODE.The CUSTOMER primary key column has no null entries,and all entries are unique.Similarly,the AGENT table's primary key is AGENT_CODE,and this primary key column also is free of null entries.

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Describe the use of nulls in a database.

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Null values are problematic in the relat...

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Character data can contain any character or symbol intended for mathematical manipulation.

A(n) ____ join only returns matched records from the tables that are being joined.

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

The DIFFERENCE operator subtracts one table from the other.

To be considered minimally relational,the DBMS must support the key relational operators ____,PROJECT,and JOIN.

A ____ is any key that uniquely identifies each row.

In a natural join,the column on which the join was made occurs twice in the new table.

____ yields a vertical subset of a table.

Fortunately,the problems inherent in the ____________________ relationship can easily be avoided by creating a composite entity.

A left outer join on tables CUSTOMER and AGENT yields all of the rows in the CUSTOMER table,including those that do not have a matching value in the AGENT table.

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.

A(n)____________________ key can be described as a superkey without unnecessary attributes.

You can think of a table as a persistent representation of a logical relation.

The ____ relational type is the "relational model ideal."

____ logic,used extensively in mathematics,provides a framework in which an assertion (statement of fact) can be verified as either true or false.

The proper use of ____________________ keys is crucial to controlling data redundancy.

There is never a good reason to use null values in a database.