Re: A better way to construct regular expressions in XML Schem

From: Rick Jelliffe <rjelliffe@allette.com.au>
To: "Costello, Roger L." <costello@mitre.org>
Date: Tue, 21 Nov 2017 10:24:01 +1100

Play the video

No.

But what makes entities offensive? Seems like the appropriate technology to use.

In Schematron, you can put the text portions into variables and combine them. But it is ultimately still just text substitution (macros). XSD doesn't provide simple macros, but it doesn't need to, because XML does with entities.

The class-based programming movement in the 80s said that it would be better to figure out all the cool things that macros (ccp, m4, etc) were used for should be elaborated into first-class language constructs for better clarity, power etc. Hence C++ and OOP. XSD is the last gasp of this movement. The trouble is that there are uncountable things people can do with even simple macros: it severely restricts the expressivity (though not the power) of the language to not have any macro mechanism. (Schematron has 3 kinds of macros, if anyone is interested: simple macros with XPath variables and abstract rules, and parameterized macros with abstract patterns. You might say Schematron itself is a macro, actually...)

Regards

Rick

On Mon, Nov 20, 2017 at 11:35 PM, Costello, Roger L. <costello@mitre.org> wrote:

Hi Folks,

I have an XML Schema that needs some complex regular expressions. I have been using <!ENTITY> to construct the regexes. See below. I find it pretty hard to debug these regular expressions. Is there a better way to construct regexes? /Roger

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xsl:schema [
<!ENTITY Language-Tag "(&lang-tag;)|(&private-use;)|(&grandfathered;)">
<!ENTITY lang-tag "(&language;)(-&script;)?(-&region;)?(-&variant;)*(-&extension;)*(-&private-use;)?">
<!ENTITY language "([&ALPHA;]{2,3}(-&extlang;)?)|([&ALPHA;]{4})|([&ALPHA;]{5,8})">
<!ENTITY extlang "[&ALPHA;]{3}(-[&ALPHA;]{3}){0,2}">
<!ENTITY script "[&ALPHA;]{4}">
<!ENTITY region "([&ALPHA;]{2})|([&DIGIT;]{3})">
<!ENTITY variant "([&alphanum;]{5,8})|([&DIGIT;][&alphanum;]{3})">
<!ENTITY extension "((&singleton;)(-[&alphanum;]{2,8})+)">
<!ENTITY singleton "([&DIGIT;])|([A-W])|([Y-Z])|([a-w])|(y-z)">
<!ENTITY private-use "x(-[&alphanum;]{1,8})+">
<!ENTITY grandfathered "(&irregular;)|(&regular;)">
<!ENTITY irregular "(en-GB-oed)|(i-ami)|(i-bnn)|(i-default)|(i-enochian)|(i-hak)|(i-klingon)|(i-lux)|(i-mingo)|(i-navajo)|(i-pwn)|(i-tao)|(i-tay)|(i-tsu)|(sgn-BE-FR)|(sgn-BE-NL)|(sgn-CH-DE)">
<!ENTITY regular "(art-lojban)|(cel-gaulish)|(no-bok)|(no-nyn)|(zh-guoyu)|(zh-hakka)|(zh-min)|(zh-min-nan)|(zh-xiang)">
<!ENTITY ALPHA "a-zA-Z">
<!ENTITY DIGIT "0-9">
<!ENTITY alphanum "(&ALPHA;)|(&DIGIT;)">
]>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

    <xs:element name="language">
        <xs:simpleType>
            <xs:restriction base="xs:string">
                <xs:pattern value="&Language-Tag;" />
            </xs:restriction>
        </xs:simpleType>
    </xs:element>

</xs:schema>

Follow-Ups:
- Re: A better way to construct regular expressions in XML Schemas?
  - From: Michael Kay <mike@saxonica.com>

References:
- A better way to construct regular expressions in XML Schemas?
  - From: "Costello, Roger L." <costello@mitre.org>

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