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From the
point of view of a business event, the following types of business
rules can be discerned:
These state how to handle
business events. For example, what to do when an order is canceled.
These instruction rules are made known to the organization using a
user manual, for example.
These define business
specific constraints on the information to be stored. They state
what is not allowed.
These express how the system
should behave in given situations. They state what the system
should do automatically.
These state how information
should be derived or calculated.
These state how the system
should present itself to the user, and how the work and tasks are
to be organized.
Restriction rules
Restriction rules define the
constraints within which information in the system is held. They
ensure that invalid information does not enter the system.
Typical examples are minimum
values, illegal combinations of values or compulsory combinations
of values. An example of a compulsory combination could be: "An
address having a post-office box number must also have a ZIP code
for this post-office box".
Together with the data model,
the restriction rules define all allowed states and all allowed
transitions in the information system. Data modeling techniques
usually include some types of restriction rules.
A special category of
restriction rule are those rules that define the authorization of
user-roles, restricting user access to certain parts of the
system.
Behavior rules
Behavior rules are all those rules performed within the system
that result in changes to data. This guarantees that all rules that
change information automatically are clustered in one group.
Together the behavior rules constitute the process performed by the
system: more precisely, the process is the chaining of behavior
rules in a given situation. Restriction rules can only limit this
process, not add to it. Examples are:
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When the supply of an article runs out, all orders that include
this article should be blocked for delivery. |
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When the stock level of an article is lower then 10, create a
supply call to the manufacturer. |
Deduction rules
Deduction rules are rules that define how to deduce or calculate
new information on the basis of existing information. Basically
there are two types of deduction rule: those based on a
calculation, and those based on formal reasoning. When a deduction
rule stores the result, we do not call it a deduction rule, but a
behavior rule. Examples are:
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A rule that calculates the total price of an order. |
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A rule that finds the delivery zone on the basis of a ZIP
code. |
Instructions
Instructions are rules that instruct users how to operate the
system in given situations. They are not implemented in the system,
but in user manuals. Instruction rules describe the proper use of
the system, and how to react to a business event. They are also
used:
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To guide the user through difficult parts of the system. |
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To enforce restrictions or deductions that are not embedded in
the system (for whatever reason). |
Instructions are written
during the iterative process of system development, to guarantee
that no knowledge related to the concept of the system is lost.
An example is an instruction
to application management: Use "UK" as the abbreviation of United
Kingdom as there are hard-coded references to this
abbreviation.
Presentation rules
All rules that describe how the system should look are called
presentation rules. Presentation rules therefore describe the
layout of windows and reports. Presentation rules do not concern
business knowledge, but they are strongly related to the internal
workflow of the organization. Examples could be:
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All primary keys should be presented with a blue border on the
screens. |
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Order-handling information and order-price information should
be clearly situated together on the screen. |
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