The principal difference between information collected in a database
versus information collected in a file is the way the data is organized.
A flat file is organized physically; certain items precede or follow
other items. But the contents of a database are organized according
to a data model. A data model is a plan, or map, that
defines the units of data and specifies how each unit relates to the
others.
For example, a number can appear in either a file or a database.
In a file, it is simply a number that occurs at a certain point in
the file. A number in a database, however, has a role that the data
model assigns to it. The role might be a price that is associated
with a product that was sold as one item of an order that
a customer placed. Each of these components, price, product,
item, order, and customer, also has a role that the data model specifies.
For an illustration of a data model, see the following figure. Figure 1: The advantage of using a
data model
You design the data model when you create the database. You then
insert units of data according to the plan that the model lays out.
Some books use the term schema instead of data
model.
