[tag-comment] Re: [tag] coments on Section 3.7.2 "COmpositionof Assertions" (V0.995)

["Stephen Green" <stephen.green@bristol.gov.uk>]

Wouldn't just dropping the prerequisite (in this case) solve it?
Surely it goes without saying that " [the widget] is conformant to 
Mini-Widget Small Box Specification 1.2)" since this is a 'Mini-Widget 
Small Box Specification 1.2' test assertion.

>>> <david_marston@us.ibm.com> 22/10/08 20:05 >>>
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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