Different kind of rules are used within an application. Business rules do have high business value. Different kinds of business rules exists in every layer within the clean architecture.
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Input validation (Interface Layer) |
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Authorization/authenticatie rules (Application Layer) |
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Process rules (Application Layer and Domain Layer) |
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Policy, Deduction, Integrity, Calculation rules (Domain Layer) |
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Business rules that might result in a negative decision (e.g. rejection of a credit application or subsidy) can be further characterized in different categories. For example, some applications distinguish between 'red' and 'orange', analogous to traffic lights. In accordance with e.g. GDPR art 22, such rules are open to review (and may be overruled) by case handlers. This review takes place without respect to the severity of the rule, as any rule might be broken in previously unforeseen circumstances. In that sense, every policy rule is ultimately a 'soft rule'. However, a useful distinction might be between rules that are open to human interpretation in every instance (e.g. open standards) versus rules for which there is no standing policy, necessitating a case-by-case approval/appeal process involving senior management.
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2 Comments
Bastiaan du Pau
There is a small discrepancy:
Unknown User (w.van.den.berg)
Well spotted. A validation rule guards against invalid data being submitted. If it is the case that any age under 18 simply cannot be processed, a validation rule should be used. In that case, an error message could be displayed.
However, it is more likely that this should actually be a domain rule. After all, 18 sounds suspiciously like the threshold for adulthood. The age at which people can enter into contracts, vote, or order alcohol are all related, and subject to change or nuance. In other words; policies!
A better example would be age >= 0 ; after all, none of us are getting younger.
For some other non-negative value, it might also be the case that underlying mechanisms rely on in some way (e.g. storing age in a database as an 'unsigned' integer that cannot be negative). The latter is meant by 'can we process this value?'. This might just be a matter of the underlying system's capabilities, rather than a law of nature.