Re: [w3c sml] [4775] Change "skip" to "lax" processing

I agree with Kirk that this is (partially) a performance issue, because 
"lax" allows/requires (1.0/1.1) the processor to try to assess the entire 
subtree, whereas "skip" says "do nothing".

But there is a deeper issue here: what do we want the SML-IF schema to 
enforce? I think the answer should be to make sure the document satisfy 
the SML-IF *structure* (and any additional contracts/extensions between 
processors). That is, if a document being transmitted is invalid, it 
should *not* be a violation of the SML-IF schema. The IF is OK in this 
case. (Just like "The Moon is bigger then the Sun" is OK English-wise.)

What this means is that whether it should be lax or skip depends on what 
the wildcard is supposed to match:

- If it's for *extension" points (so that additional information can be 
attached to the SML-IF instance, to be interpreted by processors who 
understand it), then "lax" should be used, in case the processor has a 
schema that can provide components to validate the matching 
elements/attributes.

- If it's a place-holder for the document being transmitted, then "skip" 
should be used, so that we don't let validity of individual document to 
affect the overall IF validity.

Based on this, it seems that only "DataType" needs a "skip" wildcard for 
its content (not attribute), and all the others should be "lax".

BTW, why did "DataType" have, as its content:

      <xs:any namespace="##other" processContents="skip" minOccurs="0" 
maxOccurs="unbounded"/>

I would think it should be

      <xs:any processContents="skip"/>
      <xs:any namespace="##other" processContents="lax" minOccurs="0" 
maxOccurs="unbounded"/>

That is, we expect the first element to be the document being transmitted, 
which can have any namespace (including that for SML-IF). This one is 
"skip" because we don't care about its validity. This element must appear 
once and only once. Then there are any numbers of additional elements that 
can be used for extension purposes, hence "##other" and "lax".

Thanks,
Sandy Gao
XML Technologies, IBM Canada
Editor, W3C XML Schema WG
Member, W3C SML WG
(1-905) 413-3255 T/L 969-3255
 



John Arwe <johnarwe@us.ibm.com> 
Sent by: public-sml-request@w3.org
2007-08-24 12:01 PM

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Re: [w3c sml] [4775] Change "skip" to "lax" processing







yeah, what he said (+1 from me) 
I never understood why we would prevent a validator from using schema 
components it could locate (skip), as long as they are not required (lax). 


Best Regards, John

Street address: 2455 South Road, Poughkeepsie, NY USA 12601
Voice: 1+845-435-9470      Fax: 1+845-432-9787 


"Wilson, Kirk D" <Kirk.Wilson@ca.com> 
Sent by: public-sml-request@w3.org 
08/24/2007 10:49 AM 


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[w3c sml] [4775] Change "skip" to "lax" processing








All, 
  
The email will serve to initiate the discussion of whether we should 
specify processControl=?lax? rather than the current ?skip? for wildcards 
in the SML XML Schemas. 
  
There is only one occurrence of processControl=?skip? in the SML 
specification: for the content of the smlerr:errorDataType. 
  
The original issue was raised with respect SML-IF in which 
processControl=?skip? is used for all extension elements (both xs:any and 
xs:anyAttribute) in the type definitions of this specification. 
  
Since I wasn?t involved in the original authorship of the spec, I?m not 
sure what the rationale was for the original use of ?skip?.  I assume it 
was for efficiency of the SML-IF consumer, the assumption being that the 
SML-IF would need to concern itself only with sml elements according to 
the semantics specified in SML-IF.  In my notes I have found the following 
definition of an SML-IF consumer: ?processes SML-IF documents in whole or 
in part by the semantics of this specification? (emphasis added).  Since, 
by definition, extension elements lie beyond the semantics of the spec, 
there appears to be no reason for the processor?s attempting to validate 
the extension elements.  But I would consider this a poor argument. 
  
?Skip? seems too finalistic and may not meet the requirements of SML-IF 
consumer creators and SML-IF document authors who need to build in special 
information, eg., into the ModelType, and can provide the schema for 
validation (assessment).  I suspect that something like this rationale 
underlies what appears to be the industry ?best practice? of using ?lax? 
processing.   The cost of using lax processing is undoubtedly absolutely 
minimal. 
  
I will recommend changing the spec to ?lax?, according to what is industry 
best practice.   
  
Kirk Wilson, Ph.D.
CA Inc.
Research Staff Member, CA Labs
Intellectual Property and Standards
Council of Technical Excellence
W3C Advisory Committee Representative 
Tele: + 1 603 823-7146
Fax:   + 1 603 823-7148
<mailto:kirk.wilson@ca.com>