[DFDL-WG] rationale for only allowing pattern facet on xs:string type

[Tim Kimber]

I have some sympathy with Mike's point, and I suspect that this question 
will arise regularly, for exactly the reasons that Mike has stated.

My recollection of the reasoning is as follows:
- a DFDL processor needs to deal with the representation and the logical 
values
- the representation is described by DFDL properties ( some of which can 
be inherited from XSD properties via the use of 'implicit' )
- the logical values are described/constrained by xsd facets. These will 
only be checked if validation is enabled ( or if the DFDL function 
dfdl:checkConstraints() is used in an assert/discriminator ).
- a pattern facet on an xs:string element applies to the info set value. 
- for a non-string element, it is not possible to apply a pattern facet to 
the info set value

I think this issue could be overcome if we made the rule that the pattern 
facet can only be used when representation='text' and it is applied to the 
text representation, after any padding characters have been removed. 

Some questions would then arise: 
- does this check occur before or after nil processing? 
- does a pattern of  ".+," disallow empty elements, thus preventing 
defaulting even when a default value has been supplied?

regards,

Tim Kimber, DFDL Team,
Hursley, UK
Internet:  kimbert at uk.ibm.com
Tel. 01962-816742 
Internal tel. 37246742




From:   Steve Hanson/UK/IBM at IBMGB
To:     Mike Beckerle <mbeckerle.dfdl at gmail.com>, 
Cc:     dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org
Date:   16/05/2013 09:20
Subject:        Re: [DFDL-WG] rationale for only allowing pattern facet on 
xs:string       type
Sent by:        dfdl-wg-bounces at ogf.org



It was to prevent confusion between XML schema pattern facet and DFDL text 
number and text calendar patterns. 

Regards

Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848 



From:        Mike Beckerle <mbeckerle.dfdl at gmail.com> 
To:        dfdl-wg at ogf.org, 
Date:        15/05/2013 18:51 
Subject:        [DFDL-WG] rationale for only allowing pattern facet on 
xs:string        type 
Sent by:        dfdl-wg-bounces at ogf.org 




The pattern facet is allowed on all types in XML Schema. 

DFDL says the XSDL pattern facet is for xs:string type elements only.

What is the rationale for this restriction?

We are encountering many constraints in format specs that are using XML 
Schema regular expressions, where those regex are applied to numeric types 
(e.g., xs:decimal for lattitude and longitude). 


-- 
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com
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