Suppose that we created a relation with the attributes shown in Figure 8.3.
The key of the Student relation is the composite of Sname and Dorm (assuming that no students with the
same name will live in the same dorm).
This horizontal box representation is a common way to represent a relation??”vertical lines separate the
attribute names, and the attributes that comprise the key are underlined. The key attributes do not need to be adjacent
to one another, and they do not need to be on the left side, but often people choose to show them this way.
The key of any relation is always a determinant; by definition, the key identifies the entire tuple. Given
values for Sname and Dorm in the Student relation, the values for all the other attributes are determined.
Not all determinants are keys, however. In the Student relation, there is a functional dependency between
MajorAdvisorName and AdvisorDept. Given a value for the advisor name, the department value is determined.
First normal form is simply the definition of a relation. Each attribute must be an atomic, single-valued
attribute. For example, if an attribute in the Student relation is TelephoneNumber, any one tuple in the relation
can have only one value for TelephoneNumber.
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