Re: schemas too "lax"

On Tue, Sep 3, 2013 at 11:48 AM, Michael Dolan <mdolan@newtbt.com> wrote:

> This issue is about commercial validator behavior and what are the least
> worst side affects when validating TTML documents with foreign namespace
> attributes.  This is not about TTML document conformance - the schema is
> not authoritative. It’s just a tool.  Sorry for any misunderstanding.****
>
> ** **
>
> The issue is only about which side affects you prefer in your schema
> validation:
>

you present these as an either or choice when in fact they are semantically
unrelated; that use of a strict processing mode happens to also detect
undefined attributes in one of the TT namespaces is a coincidental side
effect


> 1.       **Fail to properly validate the use of foreign namespace
> attributes unless a schema is available; or
>

Since one cannot validate foreign namespace attributes unless a schema is
available, this doesn't make much sense.


>
> **2.       **Fail to properly reject forbidden TTML attributes (e.g.
> <tt>), or misspelled permitted TTML attributes.
>
Actually they aren't forbidden, they are simply not defined.

> ****
>
> ** **
>
> I prefer #1 over #2, but perhaps it is a matter of personal or application
> preference.
>

I don't see this as a choice between #1 and #2 but two unrelated issues.


> As long as there is no implication that the W3C schema is authoritative,
> then it doesn’t really matter, I guess.
>

The W3C schema is authoritative for the purpose it was designed to meet,
and this purpose is documented in 4.1 as:

"may be used to validate a superset/subset of conformant TTML Content *Document
Instances*"

In my view, you are asking more from this schema than is intended.

My primary position is that a content conformance verification tool should
be employed, which may use either defined XSD or RNC schemas (or not), and
which verifies other conformance requirements than can be expressed in XSD.

My secondary position is that the TTML schemas we publish should remain as
close as possible to our definition of a TTML Abstract Document Type while
at the same time doing what makes sense for use of these schemas in
practical tools.

Notwithstanding the above, we might be able to improve our schemas (at
least XSD) to do a better job of
detecting non-defined attributes in TT namespaces without sacrificing lax
processing on non-TT namespaces, e.g., we might be able to use something
like:

<xs:choice>
  <xs:anyAttribute namespace="http://www.w3.org/XML/1998/namespace"
processContents="strict"/>
  <xs:anyAttribute namespace="http://www.w3.org/ns/ttml#metadata"
processContents="strict"/>
  <xs:anyAttribute namespace="http://www.w3.org/ns/ttml#parameter"
processContents="strict"/>
  <xs:anyAttribute namespace="http://www.w3.org/ns/ttml#styling"
processContents="strict"/>
  <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:choice>

I haven't checked this yet, but it seems like it might serve your goals of
#2.


> ****
>
> ** **
>
> Regards,****
>
> ** **
>
>                 Mike****
>
> ** **
>
> *From:* Andreas Tai [mailto:tai@irt.de]
> *Sent:* Monday, September 02, 2013 2:50 AM
> *To:* Glenn Adams
> *Cc:* Michael Dolan; TTWG
> *Subject:* Re: schemas too "lax"****
>
> ** **
>
> Hi Glenn, Mike,
>
> I agree with Glenn that the value "lax" best matches the original
> intention. TTML does not make any provisions about the validation of
> foreign namespace elements. An XML schema is no requirement for foreign
> namespace elements. Therefore it is possible that document authors include
> foreign namespace elements (e.g. some metadata) that are not specified in
> any schema or written specification.
>
> It is as well probable that implementations take a TTML subset/derivation
> (e.g. Subset A) as reference. If this implementation gets a TTML document
> that take Subset B as a reference where for example some extra metadata
> elements are defined it will just ignore them and process the document
> without any errors.
>
> It could be helpful to dig a bit deeper why some commercial parsers do not
> conform to the XSD standard. If this can not be fixed an additional note
> may be helpful (e.g. that in some application contexts the processContents
> attribute of xs:any and xs:anyAttribute may be set to "strict").
>
> Best regards,
>
> Andreas
>
>
> Am 01.09.2013 05:20, schrieb Glenn Adams:****
>
> Sorry, hit the Send button prematurely. See more inline: ****
>
> ** **
>
> On Sat, Aug 31, 2013 at 9:17 PM, Glenn Adams <glenn@skynav.com> wrote:****
>
> ** **
>
> On Sat, Aug 31, 2013 at 11:21 AM, Michael Dolan <mdolan@newtbt.com> wrote:
> ****
>
> The current schemas don’t reject attributes on elements that:****
>
>  ****
>
> 1.       are undefined (e.g. junk:junk=”junk”),****
>
> Since this is permissible, I'm not sure whether we want to reject. Keep in
> mind that TT validity is assessed only after removing foreign namespace
> elements and attributes. If we reject these by making the schema more
> restrictive, then it may produce a false negative assessment.****
>
> ** **
>
> The current use of processContents="lax" is defined by XSD 1.0 as follows:
> ****
>
> ** **
>
> "If the item has a uniquely determined declaration available, it must be *
> ·*valid*·* <http://www.w3.org/TR/xmlschema-1/#key-vn> with respect to
> that definition, that is, *·*validate*·*<http://www.w3.org/TR/xmlschema-1/#key-vn> if
> you can, don't worry if you can't."****
>
> ** **
>
> IMO, this seems the logically correct choice.****
>
> 2.       typos of valid attributes (e.g. ttm:descr=”t”), and****
>
> Unfortunately, this is a limitation of relying upon an XSD schema to
> solely determine validity. This is only one of a number of validity
> constraints not expressible using XSD 1.0 schemas. However, this particular
> invalidity is testable outside of XSD, and the TTV tool does test and
> report this as an error [1].****
>
> ** **
>
> [1]
> https://github.com/skynav/ttv/blob/master/tst/resources/com/skynav/ttv/app/ttml10-invalid-metadata-unknown-attributes.xml
> ****
>
> 3.       valid attributes from TTML namespaces that are forbidden (e.g.
> <tt ttm:desc=”t” …>).****
>
> Again, this is an XSD 1.0 limitation, and requires testing beyond XSD
> usage. The TTV tool does test and report this as an error [2].****
>
> ** **
>
> [2]
> https://github.com/skynav/ttv/blob/master/tst/resources/com/skynav/ttv/app/ttml10-invalid-metadata-disallowed-attributes.xml
>  ****
>
>  ****
>
> I understand that this was intentional to enable foreign namespace
> attributes without requiring their schemas.****
>
>  ****
>
> This negative side effect stems from the use ##other and
> processContents=”lax” in combination with commercial validators not even
> trying to validate when the schemaLocation is actually provided (lax is
> supposed to be “best effort”, not “just forget all about it”).****
>
> I just tested use of lax validation of a "junk:junk" attribute using ant's
> <schemavalidate/> task, which uses the platform's JAXP implementation.
> Doing a bit of snooping, I'm using:****
>
> ** **
>
> $ java -version****
>
> java version "1.6.0_51"****
>
> Java(TM) SE Runtime Environment (build 1.6.0_51-b11-457-11M4509)****
>
> Java HotSpot(TM) 64-Bit Server VM (build 20.51-b01-457, mixed mode) ****
>
> ** **
>
> $ java com.sun.org.apache.xerces.internal.impl.Version****
>
> Xerces-J 2.6.2****
>
> ** **
>
> So, back to "junk:junk", I find that it is indeed being processed with use
> of lax processing. I've tested it using two techniques, and both work:****
>
> ** **
>
> *Option #1* using xsi:schemaLocation in the instance document, e.g.****
>
> ** **
>
> <tt tts:extent="640px 480px" xml:lang="en"****
>
>   xmlns="http://www.w3.org/ns/ttml"****
>
>   xmlns:tts="http://www.w3.org/ns/ttml#styling"****
>
> *  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"*****
>
> *  xsi:schemaLocation="http://junk.com/junk junk.xsd"*****
>
>   xmlns:junk="http://junk.com/junk" junk:junk="-3"/>****
>
> ** **
>
> and****
>
> ** **
>
> *Option #2* using ant's <schemavalidate/> task's <schema/> child element
> (having removed the above xsi:schemaLocation embedded in instance document):
> ****
>
> ** **
>
> <schemavalidate fullchecking="true" warn="true">****
>
>   <schema namespace="http://www.w3.org/ns/ttml" file="${xsd.schema}"/>****
>
> *  <schema namespace="http://junk.com/junk"
> file="${examples.dir}/junk.xsd"/>*****
>
>   <fileset dir="${examples.dir}">****
>
>     <include name="ex1.xml"/>****
>
>   </fileset>****
>
> </schemavalidate>****
>
> ** **
>
> If don't create a junk.xsd file, then I get the following using Option #1:
> ****
>
> ** **
>
> $ ant validate-example-1****
>
> Buildfile: /Users/glenn/work/w3c/ttml/ttml1/spec/build.xml****
>
> ** **
>
> validate-example-1:****
>
> [schemavalidate]
> /Users/glenn/work/w3c/ttml/ttml1/spec/examples/ex1.xml:6:52:
> schema_reference.4: Failed to read schema document 'junk.xsd', because 1)
> could not find the document; 2) the document could not be read; 3) the root
> element of the document is not <xsd:schema>.****
>
> ** **
>
> BUILD SUCCESSFUL****
>
> Total time: 0 seconds****
>
> ** **
>
> For Option #2, I get:****
>
> ** **
>
> $ ant validate-example-1****
>
> Buildfile: /Users/glenn/work/w3c/ttml/ttml1/spec/build.xml****
>
> ** **
>
> validate-example-1:****
>
> ** **
>
> BUILD FAILED****
>
> /Users/glenn/work/w3c/ttml/ttml1/spec/build.xml:128: File not found:
> /Users/glenn/work/w3c/ttml/ttml1/spec/examples/junk.xsd****
>
> ** **
>
> Total time: 0 seconds****
>
> ** **
>
> If I do create junk.xsd with the following contents:****
>
> ** **
>
> <xs:schema targetNamespace="http://junk.com/junk"****
>
>   xml:lang="en" xmlns:xs="http://www.w3.org/2001/XMLSchema">****
>
>   <xs:attribute name="junk" type="xs:positiveInteger"/>****
>
> </xs:schema>****
>
> ** **
>
> then retry validation, I get:****
>
> ** **
>
> For Option #1:****
>
> ** **
>
> $ ant validate-example-1****
>
> Buildfile: /Users/glenn/work/w3c/ttml/ttml1/spec/build.xml****
>
> ** **
>
> validate-example-1:****
>
> [schemavalidate]
> /Users/glenn/work/w3c/ttml/ttml1/spec/examples/ex1.xml:6:52:
> cvc-minInclusive-valid: Value '-3' is not facet-valid with respect to
> minInclusive '1' for type 'positiveInteger'.****
>
> [schemavalidate]
> /Users/glenn/work/w3c/ttml/ttml1/spec/examples/ex1.xml:6:52:
> cvc-attribute.3: The value '-3' of attribute 'junk:junk' on element 'tt' is
> not valid with respect to its type, 'positiveInteger'.****
>
> ** **
>
> BUILD FAILED****
>
> /Users/glenn/work/w3c/ttml/ttml1/spec/build.xml:128:
> /Users/glenn/work/w3c/ttml/ttml1/spec/examples/ex1.xml is not a valid XML
> document.****
>
> ** **
>
> Total time: 0 seconds****
>
> ** **
>
> ** **
>
> For Option #2:****
>
> ** **
>
> $ ant validate-example-1****
>
> Buildfile: /Users/glenn/work/w3c/ttml/ttml1/spec/build.xml****
>
> ** **
>
> validate-example-1:****
>
> [schemavalidate]
> /Users/glenn/work/w3c/ttml/ttml1/spec/examples/ex1.xml:4:52:
> cvc-minInclusive-valid: Value '-3' is not facet-valid with respect to
> minInclusive '1' for typ\****
>
> e 'positiveInteger'.****
>
> [schemavalidate]
> /Users/glenn/work/w3c/ttml/ttml1/spec/examples/ex1.xml:4:52:
> cvc-attribute.3: The value '-3' of attribute 'junk:junk' on element 'tt' is
> not valid with res\****
>
> pect to its type, 'positiveInteger'.****
>
> ** **
>
> BUILD FAILED****
>
> /Users/glenn/work/w3c/ttml/ttml1/spec/build.xml:128:
> /Users/glenn/work/w3c/ttml/ttml1/spec/examples/ex1.xml is not a valid XML
> document.****
>
> ** **
>
> Total time: 0 seconds****
>
> ** **
>
> In conclusion, there clearly are commercial validators that do respect lax
> semantics. Perhaps the one you are using should be replaced with a newer
> model.****
>
>  ****
>
> ** **
>
> ** **
>
> ** **
>
> ** **
>
>  ****
>
> I believe that the negative side effects of this “feature” in practice far
> outweigh its benefits and would like to change this to “strict”.****
>
>  ****
>
> If a user is going to the trouble to use XML validation with the TTML
> schema, why wouldn’t they also ensure that they have schemas handy for the
> foreign namespaces in use?****
>
>  ****
>
> Regards,****
>
>  ****
>
>                 Mike****
>
>  ****
>
> Michael A DOLAN****
>
> TBT, Inc.    PO Box 190****
>
> Del Mar, CA 92014****
>
> (m) +1-858-882-7497****
>
> mdolan@newtbt.com****
>
>  ****
>
>  ****
>
> ** **
>
> ** **
>
>
>
>
> ****
>
> -- ****
>
> ------------------------------------------------****
>
> Andreas Tai****
>
> Production Systems Television IRT - Institut fuer Rundfunktechnik GmbH****
>
> R&D Institute of ARD, ZDF, DRadio, ORF and SRG/SSR****
>
> Floriansmuehlstrasse 60, D-80939 Munich, Germany****
>
> ** **
>
> Phone: +49 89 32399-389 | Fax: +49 89 32399-200****
>
> http: www.irt.de | Email: tai@irt.de****
>
> ------------------------------------------------****
>
> ** **
>
> registration court&  managing director:****
>
> Munich Commercial, RegNo. B 5191****
>
> Dr. Klaus Illgner-Fehns****
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