[imsc] Unable to normatively determine non-conformance when testing content constraints.

skynavga has just created a new issue for https://github.com/w3c/imsc:

== Unable to normatively determine non-conformance when testing 
content constraints. ==
At present, IMSC1 says the following (in Section 3) regarding 
non-conforming content:

"NOTE This specification does not specify presentation processor or 
transformation processor behavior when processing or transforming a 
non-conformant Document Instance."

At the same time, IMSC1 specifies many normative constraints on 
content. As a result of there being no defined behavior in the case of
 content non-conformance, it is effectively impossible to test these 
normative constraints in an interoperable manner. For example, one 
processor may simply ignore non-conforming content, in part or in 
whole, while another processor may attempt to detect non-conformance 
and issue a warning to the end user or abort processing.

Due to this situation, one must question to what extent the IMSC1 
specification is complete and testable.

This uncertainty may be eliminated by adding the following normative 
language:

"If a presentation or transformation processor is also a validating 
content processor, then when processing a non-conforming Document 
Instance, the following semantics shall apply:

* if validation is disabled or is otherwise not performed, then 
subsequent processing behavior is not defined;
* otherwise, processing shall depend upon the value of the application
 parameter *validationActionMode* as follows:
  * if 'abort', then processing shall be aborted;
  * if 'warn', then the end-user should be warned, with an option to 
abort or ignore;
  * if 'ignore', then should not abort or warn end-user;

The value of the *validationActionMode* application parameter may be 
determined by the document processing context, and, if not set, shall 
assume the value 'abort'.

If processing is not aborted in the case of a non-conforming Document 
Instance, then further processing behavior is not defined by this 
specification.

Note: A processor may choose to attempt to recover from a 
non-conforming Document Instance by discarding or ignoring content 
until normal processing can continue."

and, further, revising the above cited NOTE in Section 3 to read as 
follows:

"NOTE This specification does not specify presentation processor or 
transformation processor behavior when processing or transforming a 
non-conformant Document Instance when the processor is not a 
validating content processor."

The above proposal is conceptually based on new features in TTML2 
intended to deal with content conformance semantics, e.g., see [1][2],
 but does so without resorting to use of any of the new TTML2 
vocabulary.

[1] 
https://dvcs.w3.org/hg/ttml/raw-file/default/ttml2/spec/ttml2.html#profile-attribute-validation
[2] 
https://dvcs.w3.org/hg/ttml/raw-file/default/ttml2/spec/ttml2.html#profile-attribute-validationAction

As such, adding this in IMSC1 will improve our ability to verify the 
many normative statements in IMSC1 regarding content constraints, and 
do so in an interoperably testable manner. We can make available an 
additional set of test content that contains one or more tests for 
every content constraint specified in IMSC1.


Please view or discuss this issue at 
https://github.com/w3c/imsc/issues/125 using your GitHub account

Received on Saturday, 19 December 2015 03:55:16 UTC