- From: Andreas Tai <tai@irt.de>
- Date: Mon, 02 Sep 2013 11:49:32 +0200
- To: Glenn Adams <glenn@skynav.com>
- CC: Michael Dolan <mdolan@newtbt.com>, TTWG <public-tt@w3.org>
- Message-ID: <52245F2C.1010100@irt.de>
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
> <mailto:glenn@skynav.com>> wrote:
>
>
> On Sat, Aug 31, 2013 at 11:21 AM, Michael Dolan <mdolan@newtbt.com
> <mailto: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 <tel:%2B1-858-882-7497>
>
> mdolan@newtbt.com <mailto:mdolan@newtbt.com>
>
>
>
--
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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
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Received on Monday, 2 September 2013 10:55:34 UTC