SBVR — missing definitions

Referencing dtc/06-03-02, section 8.1.2 defines four basic modalities (necessity, possibility, obligation, permissibility). This agrees with table 10.2.

Section 10.1.2 defines a total of eight modes of thinking, of which one (contingency) "is not relevant in a business rules context." This leaves three alethic modes (necessity, possibility, and impossibility), and four deontic modes (permission, obligation, nonpermission/forbidden/prohibition, and non-obligation).

Table I.3 lists six modal operators: necessary, possible, impossible, obligatory, permitted, forbidden. This matches section 10.1.2 if we assume that non-obligation (like contingency) is not relevant.

Section 12.2.1 defines six forms of business rule statements: obligation, prohibitive, restricted permissive, necessity, impossibility, restricted possibility. The two restricted forms are defined as composites of either permission or possibility and a condition. Notice that unrestricted permissive and unrestricted possibility statement forms are not mentioned.

Section F.1.1 describes eight statement forms: obligative statement, prohibitive statement, restricted permission, unrestricted permission, necessity, impossibilty, restricted possibility, unrestricted possibility. It has both of the forms (unrestricted permission, unrestricted possibility) that seem to be missing from section 12.2.1.

Section 10.1.2 defines prohibition but not impossibility.

Suggestions:

1. It seems that section 12.2.1 should include the two unrestricted forms: unrestricted permission, unrestricted possibility. Alternatively, section F.1.1 should be aligned with section 12.2.1 – but that seems undesirable since the unrestricted forms do appear in the real world.
2. Section 10.1.2, in the discussion of deontic modality, should make it clear that "non-obligation" is not relevant, as it already does for "contingency" in the definition of alethic modality.
3. Make the definition of the restricted forms explicit by defining them in terms of the equivalent logical formulations using the underlying basic modalities plus implications.
4. Adopt a consistent approach to the negative forms (prohibition, impossibility):
a) Adopt one designation for nonpermission/forbidden/prohibition.
b) Define impossibility in section 10.1.2.
c) Make the definition of the negative forms (impossibility, prohibition) explicit by defining them in terms of the equivalent logical formulations using "not" and the underlying basic modalities.

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