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1 | Main | Ask yourself the question what the main decision is. If you think of more than one answer, split these decisions if possible. |
2 | Sub decisions | For each identified decision, determine if the decision is preferably built up out of meaningful sub decisions. These sub decisions could be reusable decisions - in fact reusable decisions will most likely be sub decisions - but not every sub decision has to be a reusable decision. Think of a complex calculation where intermediate results are never reused but are created nevertheless, for the sake of understandability. |
3 | Circularity | Avoid circularity. When decision A depends on the outcome of decision B and decision B needs the result of decision A as input, you're in trouble! When designing decisions top-down circular references can easily be avoided. |
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Note that a decision is not bound to be a Boolean. In general, there are three types of decisions:
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A typical example of a business rule is a rule that has a boolean as result. Let's say that any applicant can request a certain insurance, and all women receive a discount. In this particular case, a default constant value for Discount is set to False and a business rule can be created that overwrites this attribute to true whenever the applicant is female:
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Decision table
A decision table is used best when the possible outcome of the logic is one of many values. Let's say that when applying for a certain loan, a risk category is determined. Based upon applicant characteristics such as recurrence and a calculated risk score, the risk category is either very low, low, medium, high or decline.
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For more information on Decision tables and Business rules, see
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A default value, combined with an expression, is used most often when the outcome of the logic is determined/calculated by some sort of formula. See an example below, where the required monthly installment is determined by a formula containing - amongst others - monthly interest and monthly fee.
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There are two typical scenarios in which default value expressions are used:
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