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@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742

From: Steve Hanson/UK/IBM@IBMGB
To: Mike Beckerle <mbeckerle.dfdl@gmail.com>,
Cc: dfdl-wg@ogf.org, dfdl-wg-bounces@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@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@uk.ibm.com
tel:+44-1962-815848

From: Mike Beckerle <mbeckerle.dfdl@gmail.com>
To: dfdl-wg@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@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-- dfdl-wg mailing list dfdl-wg@ogf.orghttps://www.ogf.org/mailman/listinfo/dfdl-wg

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Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU