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The rule that no two rows in a table can have identical values throughout means that an
individual row can always be identified by quoting the values of all its attributes. In
many cases, however, some of the attribute values may never be needed to identify a
row. For example, it may be known that an occurrence of the table type:
Employee (employeeNo, employeeName, salary)
will never contain two rows with the same value of employeeNo, so the value of
employeeNo alone is sufficient to identify a row. In this example, employeeNo is a row
identifier for the table. Although the value of the composite attribute {employeeNo,
employeeName} would ...