A Business Rules Typology
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 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 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:
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:
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:
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.
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: