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Subject: Re: [tag] coments on Section 3.7.2 "COmposition of Assertions" (V0.995)

I see a problem when a prerequisite requires testing in order to determine eligibility. One can then build a dependency chain of the tests: e.g., you can't apply tests derived from TA 76345 until you have an outcome on any of a family of tests (list them here) that will show that the prerequisite of 76345 has been satisfied. Some of those tests may have their own prerequisites and hence dependencies, etc.

Prerequisite: [the widget] is conformant to Mini-Widget Small Box Specification 1.2
Predicate: [the widget] is conformant to WidgetSpec 1.0

<SG> the main assertion is that such a small widget is also a widget in that it conforms to the WidgetSpec 1.0
 the way this TA reads, the normative Source must be aligned with the Predicate: it should be "Conformance clause to WidgetSpec 1.0" (exactly like in widget-TA109-1)
I think it reads that you must already determine that the target is a Small Box 1.2 Mini-Widget before you can even ask about whether it is a 1.0 Widget. Circular dependency?

<SG> Surely this is just another way of saying the same thing:
"conformant to WidgetSpec 1.0" == "conforms to the conformance clause of WidgetSpec 1.0"
That equivalence is true if WidgetSpec 1.0 only has one class of product. Otherwise, it must say something like "is a conformant [class] as defined by WidgetSpec 1.0".

The presence of the prerequisite means that the TA only applies to widgets already known as confirming to Mini-Widget Small Box spec:

<SG> I agree
The problem is the "already known" part. I think this drives the debate about whether prerequisites can be based on either (1) declarations from the product provider and (2) measurable/testable properties of the implementation. A "type 2" prerequisite, if as broad as "is a conformant widget" could still exist in a formal structure of measured facts (predicates, as it were) as long as the TAs for widgets include a final "summary" TA for overall conformance.

I think you can see why I wish this example used an orthogonal spec. The example I suggested is power sources for portable devices. Specify that some but not all widgets are portable, and certain portable ones must conform to the specs about power sources.
.................David Marston
IBM Research

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