ambiguity in current TAG draft

["Durand, Jacques R." <JDurand@us.fujitsu.com>]

 

I think we have an ambiguity in current TAG draft, revealed by the SCA use case:

 

- When a normative statement is of the kind "x MUST NOT do y" , the natural way (in fact, the recommended way) to write the predicate is:

"[target x] does not do y"

 

Then, what should be the prescription level?

(a) MANDATORY?

(b) NOT PERMITTED?

 

(a) is aligned with both our definiions of predicate and of prescription level in 2.1:

   Predicate

A predicate asserts, in the form of an expression, the feature (a behavior or a property) described in the referred specification statement(s). If the predicate is an expression which evaluates to “true” over the test assertion target, this means that the target exhibits this feature. “False” means the target does not exhibit this feature.

   Prescription Level

A keyword that qualifies how imperative it is that the requirement referred in Normative Source, be met. See possible keyword values in the Glossary.

 

(b) is aligned with the Glossary definition of prescription level :

 

    The test assertion defines a normative statement which may be mandatory (MUST/REQUIRED), not permitted (MUST NOT), permitted (MAY/OPTIONAL) preferred (SHOULD/RECOMMENDED) or not recommended (SHOULD NOT). This property can be termed its prescription level.

 

The problem I see with allowing/recommending "negative" prescription levels, is that this entices the TA writer to write "negative" predicates (=true means violation), e.g.:

 

normative source: x MUST NOT do y

target: x

predicate: [target x] does y

prescription level: not permitted

 

Which so far we do not endorse.

 

while:

normative source: x MUST NOT do y

target: x

predicate: [target x] does not do y

prescription level: not permitted

 

Would be confusing and sound like a double negation ("not permitted" for target to NOT do y)

 

Do we really need negative prescription levels, and if yes how do they work?

 

Jacques