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Translating Business
Rules into Data Model
Components
Business rules set the stage for the
proper identifcation of entities,
attributes, relationships, and constraints.
In the real world, names are used to
identify objects. If the business
environment wants to keep track of the
objects, there will be specifc business
rules for the objects. As a general rule, a
noun in a business rule will translate into
an entity in the model, and a verb (active
or passive) that associates the nouns will
translate into a relationship among the
entities. For example, the business rule “a
customer may generate many invoices”
contains two nouns (customer and
invoices) and a verb (generate) that
associates the nouns. From this business
rule, you could deduce the following:
• Customer and invoice are objects of
interest for the environment and should be
repre-�
sented by their respective entities.• Tere
is a generate relationship between
customer and invoice.
To properly identify the type of
relationship, you should consider that
relationships are bidirectional; that is,
they go both ways. For example, the
business rule “a customer may generate
many invoices” is complemented by the
business rule “an invoice is generated by
only one customer.” In that case, the
relationship is one-to-many (1:M).
Customer is the “1” side, and invoice is
the “many” side.
As a general rule, to properly identify �
the relationship type, you should ask
two questions:
• How many instances of B are related to
one instance of A?• How many instances
of A are related to one instance of B?
For example, you can assess the
relationship between student and class by
asking two questions:
• In how many classes can one student
enroll? Answer: many classes.• How many
students can enroll in one class? Answer: �

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