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Re: [xml-dev] Proposal: create a repository of reusable regular expressionsusing XML ENTITY declarations

On 22/10/2012 15:39, Costello, Roger L. wrote:
> Hi Folks,
> Suppose that you wish to record the date and time of the launch of a new product. You could format the data using the xs:dateTime data type, but you desire slightly different format:
> <launch>
>     <date-time>22 Oct 2012 07:52:00 -0004</date-time>
> </launch>
> The value of <date-time> can constrained to the desired format by using an XML Schema pattern facet. Recall that the value of a pattern facet is a regular expression (regex).
> Recently I learned from Michael Sperberg-McQueen a fantastic way of creating reusable regular expressions: create XML ENTITY declarations that express the regexes.
> Recall that an XML ENTITY declaration has a name followed by its replacement text:
> <!ENTITY name "replacement text">
> So, we could create a date-time ENTITY with a regex as its replacement text:
> <!ENTITY date-time "... regex ...">
> Okay, I did just that.
> I created a file containing the ENTITY declarations for the date-time format. I created the date-time format systematically through a series of ENTITY declarations:
> ---------------------------------------------------
>             	regex-repository.ent
> ---------------------------------------------------
> <!--
>       *********************************
>           Regex for date-time
>       Here is an example string that
>       conforms to the date-time regex:
>       22 Oct 2012 07:52:00 -0004
>       *********************************
>   -->
> <!ENTITY date-time      	"(&day-of-week;)?&date;&time;">
> <!ENTITY day-of-week 	"(&WSP;)?&day-name;">
> <!ENTITY day-name      	"(Mon|Tue|Wed|Thu|Fri|Sat|Sun)">
> <!ENTITY date                	"&day;&month;&year;">
> <!ENTITY day                 	"(&WSP;)?[&DIGIT;]{1,2}&WSP;">
> <!ENTITY month            	"(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)">
> <!ENTITY year                	"&WSP;[&DIGIT;]{4,}&WSP;">
> <!ENTITY time                	"&time-of-day;&zone;">
> <!ENTITY time-of-day  	"&hour;&COLON;&minute;(&COLON;&second;)?">
> <!ENTITY hour               	"[&DIGIT;]{2,2}">
> <!ENTITY minute           	"[&DIGIT;]{2,2}">
> <!ENTITY second           	"[&DIGIT;]{2,2}">
> <!ENTITY zone               	"&WSP;[+-][&DIGIT;]{4,4}">
> <!ENTITY SP             	"&#32;">            	<!-- Space -->
> <!ENTITY HTAB           	"&#9;">             		<!-- Horizontal tab -->
> <!ENTITY WSP            	"(&HTAB;|&SP;)">    	<!-- Whitespace -->
> <!ENTITY COLON 	"&#58;">
> <!ENTITY DIGIT 	"0-9">
> The regex for date-time can be reused by any XML Schema. More precisely, the regex can be reused by referencing, in a pattern facet, the date-time ENTITY declaration.
> Here I create an XML Schema for the <launch> element and use DOCTYPE to provide access to the regexes in regex-repository.ent. I use a pattern facet to constrain the value of the <date-time> element. The value of the pattern facet is the regex found by referencing the date-time ENTITY.
> ---------------------------------------------------
>             	       launch.xsd
> ---------------------------------------------------
> <?xml version="1.0" encoding="UTF-8"?>
> <!DOCTYPE xs:schema SYSTEM "regex-repository.ent">  <<---- Get access to the regexes here
> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema";>
>      <xs:element name="launch">
>          <xs:complexType>
>              <xs:sequence>
>                  <xs:element name="date-time" maxOccurs="unbounded">
>                      <xs:simpleType>
>                          <xs:restriction base="xs:string">
>                              <xs:pattern value="&date-time;"/>   <<---- I use the regex here
>                          </xs:restriction>
>                      </xs:simpleType>
>                  </xs:element>
>              </xs:sequence>
>          </xs:complexType>
>      </xs:element>
> </xs:schema>
> Reusing a regex is simply a matter of referencing the ENTITY that holds it.
> I think it would be useful to create a repository of regular expressions using this XML ENTITY technique.
> Thoughts?
> /Roger

Of course if you just use a regex then you don't get any data 
information passed to the application, it's just a string. This is the 
classic SGML/XML view of attributes but not what a user of XSD might 
possibly expect.

There is the proposed ISO/IEC  extensible datatypes spec (mainly for use 
with RelaxNG but could be used with other schema languages)


That allows you not only to constrain the input syntax using regex but 
also to express the underlying datatype fields


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