Database Reference
In-Depth Information
pact analysis would be to use data modeling to determine what impact modifying
its structures would have on purchased software.
•
Reverse engineer
. We can derive a data model from an existing application by ex-
amining the application's database and building a data model of its structures. The
technical term for the process of building data models from existing applications is
“reverse engineering.” The trend in many industries is to purchase software and to
build less internally; therefore, our roles as modelers are expanding and changing.
Instead of modeling a new application, the data modeler may capture the informa-
tion in existing applications.
•
Understand the business
. As a prerequisite to a large development effort, it usu-
ally is necessary to understand how the business works before you can understand
how the applications that support the business will work. Before building an order
entry system, for example, you need to understand the order entry business pro-
cess. The data and relationships represented in a data model provide a foundation
on which to build an understanding of business processes.
•
Knowledge transfer
. When new team members need to come up to speed or de-
velopers need to understand requirements, a data model is an effective explanatory
medium. Whenever a new person joined our department, I spent some time walk-
ing through a series of data models to educate the person on concepts and rules as
quickly as possible.
D
ATA
M
ODELING
I
S
N
OT
O
PTIONAL!
The power of the data model as a tool to confirm and document our understanding of differ-
ent perspectives has, as the root of its power, one word:
Precision
. Precision
,
with respect
to data modeling, means that there is a clear, unambiguous way of reading every symbol
and term on the model. You might argue with others about whether the rule is accurate, but
that is a different argument. In other words, it is not possible for you to view a symbol on a
model and say, “I see A here” and for someone else to view the same symbol and respond,
“I see B here.” In a data model, precision is primarily the result of applying a standard set
of symbols. The traffic circles the gas station attendant drew for me were standard symbols
that we both understood. There are also standard symbols used in data models, as we will
discover shortly.
The process of understanding and precisely documenting data is not an optional process.
As long as there is at least some data in the application and at least two people involved in
