[DFDL-WG] Future feature? allow pattern facet on numbers when textNumberRep="standard" and representation="text"

Wed Dec 20 08:49:17 PST 2023

No, I think what you say is correct.  My point is that DFDL 1.0 does not
just disallow pattern facets on numbers because some elements might have
binary rep, but also because even if the rep is text, the original text is
not in the infoset, and therefore not available at validation time, which
is when the facet is applied.

On Wed, Dec 20, 2023 at 2:24 PM Mike Beckerle <mbeckerle at apache.org> wrote:

> Don said "...regex within XSD Schema only applies to xs:string types."
>
> I checked P. Walmsley's book "Definitive XML Schema" (which is my Bible)
> and it says pattern facets are allowed on all the string, numeric, and
> date/time types.
>
> To be clear, this is not allowed in DFDL v1.0 (because binary numbers are
> not text, so pattern facets wouldn't make sense in those cases), but
> pattern facets are allowed in in XSD 1.0, because well, everything is text
> in XML.
>
> Am I misunderstanding something?
>
>
> On Tue, Dec 19, 2023 at 11:18 PM Brutzman, Donald (Don) (CIV) <
> brutzman at nps.edu> wrote:
>
>> We’ve handled a really wide range of floats and integers in X3D graphics
>> models, and have found that xsd:schema types are very useful.  Unusual edge
>> cases (for advanced error detection) can be handled with patterns (in the
>> case of X3D, we have regex).
>>
>>
>>
>> Only limitation with this approach is that you typically have to pick one
>> or the other, since regex within XSD Schema only applies to xs:string
>> types.  Sometimes using xs:schema as primary with separate regex evaluation
>> is useful in a tool.  You may have more flexibility about hybrid approaches
>> in DFDL.
>>
>>
>>
>>    - X3D Regular Expressions (regexes)
>>    - X3D Regular Expressions (regexes) are used to validate the
>>    correctness of string and numeric array values in an X3D scene.
>>    - https://www.web3d.org/specifications/X3dRegularExpressions.html
>>
>>
>>
>> Opinion: the worst errors are the ones that remain undetected.
>>
>>
>>
>> Season’s Greetings!  8)
>>
>>
>>
>> all the best, Don
>>
>> --
>>
>> Don Brutzman  Naval Postgraduate School, Code USW/Br
>> brutzman at nps.edu
>>
>> Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA
>> +1.831.656.2149
>>
>> X3D graphics, virtual worlds, navy robotics
>> https://faculty.nps.edu/brutzman
>>
>>
>>
>> *From:* dfdl-wg <dfdl-wg-bounces at lists.ogf.org> *On Behalf Of *Mike
>> Beckerle
>> *Sent:* Tuesday, December 19, 2023 1:56 PM
>> *To:* DFDL-WG <dfdl-wg at ogf.org>
>> *Subject:* [DFDL-WG] Future feature? allow pattern facet on numbers when
>> textNumberRep="standard" and representation="text"
>>
>>
>>
>> It has come up often now that DFDL cannot be strict enough about text
>> number formats because our ICU-based textNumberPattern isn't strict enough
>> or expressive enough of subtle syntax variations.
>>
>>
>>
>> I suggest this could be fixed by just allowing the XSD pattern facet to
>> be used on numeric types when they are known textual and standard (not
>> zoned).
>>
>>
>>
>> For example dfdl:textNumberPattern="00.####" will allow the number "99."
>> to be accepted. There's currently no way to say "when it's an integer,
>> there cannot be a decimal point".
>>
>>
>>
>> People are resistant to the notion that this requires a complex type with
>> a bunch of different elements with different textNumberFormats so that you
>> have an '<int>99</int>' or <dec>99.9</dec> element. They really don't want
>> there to be different paths to this value in the infoset just because of
>> this format issue about the decimal point. It's a painful loss of
>> polymorphism in these path expressions. Instead of a simple path expression
>> to obtain such a value you end up with
>>
>>
>>
>> if (fn:exists(path/int)) then path/int else path/dec
>>
>>
>>
>> Note that DFDL's expression language has no let statement, so in the
>> above if "path" is actually "a/b/c/d/e/f/g" i.e., a typical deep path
>> (which commonly have much longer path steps than my single-letters), then
>> that path is going to be repeated 3 times in the expression. This is pretty
>> unpleasant.
>>
>>
>>
>> Rather than come up with a bunch of ICU mods to tighten up all the places
>> it is lax, and to add features for suppressed decimal points, etc. we could
>> just allow the pattern facet on textual numbers.
>>
>>
>>
>> Then the pattern facet could be "\d\d|\d\d\.\d{1,4}" which would achieve
>> the goal of enforcing the precise pattern desired if you validate after
>> parsing and before unparsing. It would not prevent conversion of the text
>> to the corresponding numeric type, but it would allow an additional tighter
>> check on what the text was.
>>
>>
>>
>> Regular XML Schema allows the pattern facet on all the numeric types, so
>> we would be eliminating what is currently a DFDL restriction, on condition
>> of only when the numeric types have standard text representation.
>>
>>
>>
>> Thoughts?
>>
>>
>> Mike Beckerle
>>
>> Apache Daffodil PMC | daffodil.apache.org
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>>
>>
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-- 
Regards
Steve
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