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In-Depth Information
Business rules
are policies enforced by a company for its various busi-
ness processes. For example, the company might require that each pur-
chase be approved by three people holding specific titles (purchasing
agent, manager of accounts payable, project manager). Business rules may
or may not be implemented in your model, but they need to be docu-
mented because eventually you need to implement them somewhere.
Whether you implement them as a relationship in the model, use a trigger
in SQL Server, or even implement them through an application, it is im-
portant to understand them early, because the model design will be driven
by the business rules that it needs to support. In Chapter 6 we also look at
the iterative process of working with stakeholders in the company. They
not only have to sign off on the initial model, but both you (as the designer)
and they (as the customer) will have changes that need to be made as the
process moves forward.
Next, we discuss the business review of the model. It's crucial to get
your customers' buy in and sign-off of the logical model. Once the cus-
tomer has approved the model, you can document releases and work to-
ward the agreed-upon system.
We cannot reiterate this point enough: You cannot skip this step. It will
save you days of pain down the line if the company needs to make changes
to the requirements. If you have agreed-upon release cycles, then you can
simply add new changes at the expense of the project's time line or of other
requirements. Without this agreement, you will be engaged in discussions,
even arguments, about the changes, and either your customer or your
modeling team will end up dissatisfied with the outcome.
Building the Logical Model
In Part III, we get to the actual building of the model. By this time, you
will have a grasp of the requirements and it will be time to translate them
into the model. We will walk you through the thought process you go
through when building a model and translate the requirements from
Mountain View Music.
Creating the Logical Model
The first step in building the logical model is to sit down and create the
model from the requirements. This is the bulk of the work of building the
logical model. In Chapter 7, Creating the Logical Model, we look at how
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