NORMALIZING A DATA MODEL - A Developer's Guide to Data Modeling for SQL Server - page 82

(1NF), second normal form (2NF), and third normal form (3NF). After
these initial normal forms were developed, research indicated that they
could result in update anomalies, so three additional forms were developed
to deal with these issues: fourth normal form (4NF), fifth normal form
(5NF), and the Boyce-Codd normal form (BCNF). There has been re-
search into a sixth normal form (6NF); this normal form has to do with
temporal databases and is outside the scope of this topic.
It's important to note that the normal forms are nested. For example, if
a database meets 3NF, by definition it also meets 1NF and 2NF. Let's take
a brief look at each of the normal forms and explain how to identify them.

First Normal Form (1NF)
In first normal form, every entity in the database has a primary key at-
tribute (or set of attributes). Each attribute must have only one value, and
not a set of values. For a database to be in 1NF it must not have any re-
peating groups . A repeating group is data in which a single instance may
have multiple values for a given attribute.
For example, consider a recording studio that stores data about all its
artists and their albums. Table 4.1 outlines an entity that stores some basic
data about the artists signed to the recording studio.

Table 4.1 Artists and Albums: Repeating Groups of Data

Album

Artist Name Genre Album Name Release Date

The Awkward Stage Rock Home 10/01/2006

Girth Metal On the Sea 5/25/1997

Wasabi Peanuts Adult Contemporary Rock Spicy Legumes 11/12/2005

The Bobby R&B Live! 7/27/1985

Jenkins Band Running the Game 10/30/1988

Juices of Brazil Latin Jazz Long Road 1/01/2003

White 6/10/2005

Notice that for the first artist, there is only one album and therefore
one release date. However, for the fourth and fifth artists, there are two al-
bums and two release dates. In practice, we cannot guarantee which re-
lease date belongs to which album. Sure, it'd be easy to assume that the
first release date belongs to the first album name, but how can we be sure