THE DATA WAREHOUSE - Fundamentals of Database Management Systems - page 344

Charges for patient
F. Jones' blood transfustion
on Oct. 11

Oct. 10

Oct. 11 $800

Oct. 12

Oct. 13

Oct. 14

Oct. 15

Oct. 16

F IGURE 13.4
Hospital patient tracking and billing
system data with three dimensions

Patient

data in relational databases. A way to store multidimensional data in a relational
database structure is with a model known as the star schema . The name comes
from the visual design in which the subject is in the middle and the dimensions
radiate outwards like the rays of a star. As noted earlier, Smith & Nephew employs
the star schema design for its data warehouse, as does Hilton Hotels for at least part
of its data warehouse environment.

General Hardware Co. Data Warehouse
Figure 13.5 repeats the General Hardware relational database and Figure 13.6 shows
a star schema for the General Hardware Co., with SALE as the subject. Star schemas
have a ''fact table,'' which represents the data warehouse ''subject,'' and several
''dimension tables.'' In Figure 13.6, SALE is the fact table and SALESPERSON,
PRODUCT, and TIME PERIOD are the dimension tables. The dimension tables
will let the data in the fact table be studied from many different points of view.
Notice that there is a one-to-many relationship between each dimension table entity
and the fact table entity. Furthermore, the '' one side'' of the relationship is always
the dimension table and the '' many side'' of the relationship is always the fact table.
For a particular salesperson there are many sales records, but each sales record is
associated with only one salesperson. The same is true of products and time periods.
To begin to understand this concept and see it come to life, refer back to the
SALES table in Figure 13.5, in which General Hardware keeps track of how many
units of each product each salesperson has sold in the most recent time period, say