First Normiai Form INF

To be in first normal form, a relation must have no repeating groups or multi-valued attributes. The class and grade fields in Figure 2.10 area good example of a non-relational design.

Figure 2. IO Decomposition to first normal form (I NF)

Figure 2. IO Decomposition to first normal form (I NF)

Each student record maintains the names of up to four classes and grades. To be a relational table, each attribute, or field, must represent a unique, discrete fact about the entity. The fields in the example relations represent duplication of the data.

It is a simple matter to reduce this relation to first normal form by merely introducing a child relation to the database called GRADES. The new structure of STUDENTS will now contain only unique records and the entries in the GRADES relation will be made unique by the combination of the Student-ID and Class fields into a composite key. The connection between these two tables will be a one-to-many relationsh

Chapter 2—Logical and Physical Database Design

based upon the Student J D being the primary key in the STUDENT& table and a foreign key in the GRADES table.

The benefits of a table being in first normal form are easy to enumerate. First, you are now working with simpler data structures. Second, . the tables are now in a state from which further normalization can occur, and finally, these structures are much easier to move from the logical data model to a physical one.

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