# Concepts of dimensional data modeling

To build a dimensional database, you start with a dimensional data model. The dimensional data model provides a method for making databases simple and understandable. You can conceive of a dimensional database as a database cube of three or four dimensions where users can access a slice of the database along any of its dimensions. To create a dimensional database, you need a model that lets you visualize the data.

Suppose your business sells products in different markets and you
want to evaluate the performance over time. It is easy to conceive
of this business process as a cube of data, which contains dimensions
for time, products, and markets. The following figure shows this dimensional
model. The various intersections along the lines of the cube would
contain the measures of the business. The measures correspond
to a particular combination: product, market, and time data.

Figure 1. A dimensional model of a business that has
time, product, and market dimensions

Another name for the dimensional model is the star schema.
The database designers use this name because the diagram for this
model looks like a star with one central table around which a set
of other tables are displayed. The central table is the only table
in the schema with multiple joins connecting it to all the other tables.
This central table is called the fact table and the other
tables are called dimension tables. The dimension tables
all have only a single join that attaches them to the fact table,
regardless of the query. The following figure shows a simple dimensional
model of a business that sells products in different markets and evaluates
business performance over time.

Figure 2. A typical
dimensional model