[DFDL-WG] Future feature? allow pattern facet on numbers when textNumberRep="standard" and representation="text"
Brutzman, Donald (Don) (CIV)
brutzman at nps.edu
Wed Dec 20 09:52:06 PST 2023
Agreed that DFDL being able to have multiple forms of value validation seems like a good idea, as indicated previously.
Agreed Priscilla’s work is always great.
Looking at the authoritative reference for XML Schema:
* W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes
* W3C Recommendation 5 April 2012
* https://www.w3.org/TR/xmlschema11-2
* Appendix G. Regular expressions
* https://www.w3.org/TR/xmlschema11-2/#regexs
* “A ·regular expression· R is a sequence of characters that denote a set of strings L(R). When used to constrain a ·lexical space·, a regular expression R asserts that only strings in L(R) are valid ·literals· for values of that type.”
For a few XML schema-capable tools, have found that either the xsd datatype expressions or the regex pattern (but not both) are supported at validation time. YMMV.
* X3D 4.0 XML Schema
* http://www.web3d.org/specifications/x3d-4.0.xsd
* excerpt:
<xs:simpleType name="SFFloat">
<xs:annotation>
<xs:appinfo>
<xs:attribute name="defaultValue" type="SFFloat" default="0.0"/>
<!-- https://stackoverflow.com/questions/10516967/regexp-for-a-double -->
<xs:pattern value="\s*([+-]?((0|[1-9][0-9]*)(\.[0-9]*)?|\.[0-9]+)([Ee][+-]?[0-9]+)?)\s*"/>
SFFloat is a single-precision floating-point type.
</xs:appinfo>
<xs:documentation source="https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-IS.proof/Part01/fieldsDef.html#SFFloatAndMFFloat"/>
</xs:annotation>
<xs:restriction base="xs:float"/>
</xs:simpleType>
Meanwhile, just tested with XMLSpy: defining both at once is allowed as a valid XML schema construct.
<xs:restriction base="xs:float">
<xs:pattern value="\s*([+-]?((0|[1-9][0-9]*)(\.[0-9]*)?|\.[0-9]+)([Ee][+-]?[0-9]+)?)\s*"/>
</xs:restriction>
The detailed requirements for how XML Schema validation can support multiple requirements is provided in the following paragraphs.
* 4.1.4 Simple Type Definition Validation Rules
* https://www.w3.org/TR/xmlschema11-2/#defn-validation-rules
* 4.1.5 Constraints on Simple Type Definition Schema Components
* https://www.w3.org/TR/xmlschema11-2/#defn-coss
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: Steve Hanson <smhdfdl at gmail.com>
Sent: Wednesday, December 20, 2023 8:49 AM
To: mbeckerle at apache.org
Cc: Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>; DFDL-WG <dfdl-wg at ogf.org>
Subject: Re: [DFDL-WG] Future feature? allow pattern facet on numbers when textNumberRep="standard" and representation="text"
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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto: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
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