[DFDL-WG] Fw: clarification needed: 16.3.1 and totalDigits, fractionDigits and textNumberPattern compatibility checks

[Steve Hanson]

Agreed that the statement should be dropped from the spec. DFDL 
implementations are free to issue a warning if they detect such a mismatch 
(so the IBM DFDL check will change from an error to a warning). 

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
----- Forwarded by Steve Hanson/UK/IBM on 28/08/2013 16:31 -----

From:   Steve Hanson/UK/IBM
To:     dfdl-wg at ogf.org, 
Date:   22/08/2013 16:02
Subject:        Re: [DFDL-WG] clarification needed: 16.3.1 and 
totalDigits, fractionDigits and textNumberPattern compatibility checks


To comply with the spec as stated, the actual check implemented by IBM 
DFDL is that the number of fraction/total digits in the DFDL 
textNumberPattern must not exceed the number of fraction/total digits 
specified by the facet.  That's a more liberal interpretation of 'match' 
but makes sense.

However the spec does not say that the textNumberPattern should not be 
allowed to describe a number greater than any maxInclusive/maxExclusive 
facet. And I don't think that there are any other checks to see that DFDL 
properties clash with schema facets.

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" <dfdl-wg at ogf.org>, 
Cc:     Jessie Chab <jchab at tresys.com>
Date:   22/08/2013 15:35
Subject:        [DFDL-WG] clarification needed: 16.3.1 and totalDigits, 
fractionDigits and textNumberPattern compatibility checks
Sent by:        dfdl-wg-bounces at ogf.org




The spec says that these need to be compatible.

"If the pattern uses digits/fractions then these must match any XML schema 
facets."

We've fallen into this trap before. Facet constraints are about the 
logical value, not the physical rep, and so must make equal sense for 
binary representations as text representations.

I was considering what kinds of static cross checks would make sense here.

Example: suppose fractionDigits='2'.

Suppose textNumberPattern="##"

the type must be xs:decimal since that's the only type that can have 
fractionDigits constrained in DFDL.

Is there a conflict of the facet with the textNumberPattern? I think not. 
Even though the pattern doesn't allow for any fractional part to be 
expressed, that means that all values will have less than or equal to 2 
fractional digits (because no fractional digits always satisfies that.)

Now suppose textNumberPattern="#.########"

Now the textNumberPattern will parse and accept things like 1.234 which 
have more than 2 fraction digits, but suppose the data simply doesn't 
contain any such. So all number in the data will obey the less than or 
equal to 2 fractional digits.

Lastly, suppose textNumberPattern="9.9999"

So, interpreted naively, this requires the data to contain 5 digits, so 
this seems inconsistent with fractionDigits of 2. 

However, we know this depends on the strict/lax behavior of ICU libraries, 
and I believe this will happily parse the data "0.0" without error. Hence 
the data could still all have 2 or fewer fractional digits.

So, I think this idea that the totalDigits and fractionDigits facets can 
be cross-checked with the textNumberPattern is spurious and we should drop 
it.

I think it dates from a time when we were still confused about the 
separation of the DFDL Infoset, and facet constraints on its value spaces, 
which are abstract, versus the XML Infoset, where everything truly is a 
string as well as whatever its XML Schema type says.

Comments?

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