Current issue with "TA for properties"

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

A medium technical issue with the current TAG draft:

 

In section 3.3 "TA  for Properties":

 

We recommend to mention the property ("medium-sized" ) in the Prescription element:

 

Prescription Level: medium-sized:mandatory

 

Because we want the prescription level to be associated with the definition of this property.

 

[requirement 104] “A widget that weighs between 100g and 300g and is from 5 to 15 centimeters long in its longer dimension, is a medium-size widget.”

 

Suggestion: instead of this, use a tag for expressing the association of the TA to the property:

 

Prescription Level: mandatory

Tag: normative_property = medium-sized

 

Rationale:

 

- very close association between the Property and the Prescription level (as currently suggested) is a bad idea: it seems to suggest that the TA  "widget-TA104-1" MUST evaluate to true (mandatory) for the property to be verified.

But that does not work if  [requirement 104] has "or" instead of "and" :

[requirement 104] “A widget that weighs between 100g and 300g OR is from 5 to 15 centimeters long in its longer dimension, is a medium-size widget.”

In that case we only want to indicate that the two TAs involved are related to the definition of this property, nothing more, as you could still satisfy the property even if you fail either TA. The Prescription level should only reflect the wording in the requirement, not be interpreted as a conformance statement.

 

- a "normative property" should ultimately not be treated differently from a conformance profile. In both cases we don't want the Prescription level to be too closely associated with the profile or property (which may require a more complex combination of TAs, to be verified). Using a Tag is more appropriate for such a loose association, whcih has simply the value of an annotation (grouping) with no other formal semantics. 

 

- The TA could be associated with several properties.

 

Jacques