Chapter 4 - Normalizing a Data Model

Data normalization is probably one of the most talked-about aspects of database modeling. Before building your data model, you must answer a few questions about normalization. These questions include whether or not to use the formal normalization forms, which of these forms to use, and when to denormalize.

First Normal Form (1NF)

In first normal form, every entity in the database has a primary key attribute (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 repeating 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

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 White	Long Road	1/01/2003 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 albums and two release dates. In practice, we cannot guarantee which release 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 that album names and dates are always entered in order and not changed afterward?

There are two ways to eliminate the problem of the repeating group. First, we could add new attributes to handle the additional albums, as in Table 4.2.

Table 4.2 Artists and Albums: Eliminate the Repeating Group, but at What Cost?

Artist Name	Genre	Album Name 1	Release Date 1	Album Name 2	Release Date 2
The Awkward Stage	Rock	Home	10/01/2006	Null	Null
Girth	Metal	On the Sea	5/25/1997	Null	Null
Wasabi Peanuts	Adult Contemporary Rock	Spicy Legumes	11/12/2005	Null	Null
The Bobby Jenkins Band	R&B	Running the Game	7/27/1985	Live!	10/30/1988
Juices of Brazil	Latin Jazz	Long Road	1/01/2003	White	6/10/2005

We've solved the problem of the repeating group, and because no attribute contains more than one value, this table is in 1NF. However, we've introduced a much bigger problem: what if an artist has more than two albums? Do we keep adding two attributes for each album that any artist releases? In addition to the obvious problem of adding attributes to the entity, in the physical implementation we are wasting a great deal of space for each artist who has only one album. Also, querying the resultant table for album names would require searching every album name column, something that is very inefficient.

If this is the wrong way, what's the right way? Take a look at Tables 4.3 and 4.4.

Table 4.3 The Artists

ArtistName	Genre
The Awkward Stage	Rock
Girth	Metal
Wasabi Peanuts	Adult Contemporary Rock
The Bobby Jenkins Band	R&B
Juices of Brazil	Latin Jazz

Table 4.4 The Albums

AlbumName	ReleaseDate	ArtistName
White	6/10/2005	Juices of Brazil
Home	10/01/2006	The Awkward Stage
On the Sea	5/25/1997	Girth
Spicy Legumes	11/12/2005	Wasabi Peanuts
Running the Game	7/27/1985	The Bobby Jenkins Band
Live	10/30/1988	The Bobby Jenkins Band
Long Road	1/01/2003	Juices of Brazil

We've solved the problem by adding another entity that stores album names as well the attribute that represents the relationship to the artist entity. Neither of these entities has a repeating group, each attribute in both entities holds a single value, and all of the previously mentioned query problems have been eliminated. This database is now in 1NF and ready to be deployed, right? Considering there are several other normal forms, we think you know the answer.