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Subject: RE: Prescription levels

its a slippery slope to expect the TA to tell "what you can conclude about the product".
So far the TC has been careful staying away from associating TAs with any conformance conclusions. These are left to test cases / test suites (resulting in "pass" or "fail").
All we have with a TA, is an indicator of fulfillment / violation of some spec requirement.
Back to our concern, I take it from your email that.. you agree with previous thread consensus:
The result of the predicate, qualified with the PL, reflects the spec requirement.
if spec tells "x MUST NOT do y"
TA: predicate=not(x does y) + PL="mandatory" is a good TA
TA: predicate=(x does y) + PL="not permitted" is a good TA
TA: predicate=not(x does y) + PL="not permitted" is NOT a good TA

From: david_marston@us.ibm.com [mailto:david_marston@us.ibm.com]
Sent: Wednesday, December 03, 2008 12:28 PM
To: tag-comment@lists.oasis-open.org
Cc: Durand, Jacques R.; stephen.green@documentengineeringservices.com
Subject: Prescription levels

I may have said this before, but I'll say it again because it helps clarify what Prescription Levels can do in the larger context: the set of Prescription Levels must be considered extensible, so that a user of TAs can integrate TAs for conformance with TAs for other purposes, such as product requirements.

The relationship between the Predicate and the Prescription Level then becomes the following:
When the Predicate is true, the Prescription Level tells you what you can conclude about the product.

Examples: Predicate true on a TA that is Mandatory: product fulfills a spec requirement.
Predicate true on a TA that is Recommended: product exhibits a trait that is considered desirable. (If the predicate were false, you could not conclude that the product is "bad" on the basis of that TA alone.)
Product X has predicate true on a product-specific TA that is a version 1.5 required feature: Product X implements one of the features that version 1.5 needed to have. (Vendor-extension TA.)
Predicate true on a TA that is Must Not: product violates a spec requirement.

I see negative Prescription Levels as being useful for testable requirements that are widespread. For example, the requirements for a well-formed XML document, such as the requirement that no element name can contain a space, can pervade the testing of a product that produces XML documents. A TA to express "no element name can contain a space" may work better as a negative, so that the predicate can be "element name contains a space". Also consider the implications of a TA for some spec (not the XML spec itself) that requires the document to be well-formed XML. Somewhere, there needs to be a "grand union" TA that says a document is considered well-formed if it passes dozens of TAs that constitute the individual requirements for well-formed-ness. It might not be a simple AND relation of the dozens of TAs, but an AND of the ones with Mandatory prescription level plus a NOT of the OR of all the ones with a Must Not prescription level.
.................David Marston
IBM Research

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