RELAX: Schemas Don't Have to be Hard

Elliotte Rusty Harold

Wednesday, March 21, 2007

elharo@metalab.unc.edu

http://www.cafeconleche.org/

What are Schemas?

Generically, a document that describes what a correct document may contain
Specifically, a very complex and baroque W3C Recommendation for an XML-document syntax that describes the permissible contents of XML documents
But there other options!

About RELAX NG

Created by James Clark and Murata Makoto
Based on TREX and RELAX
Formal theory is hedge automata
ISO standard: ISO/IEC 19757-2:2002(E), Document Schema Definition Languages (DSDL) — Part 2:Regular-grammar-based validation — RELAX NG, I

What's Wrong with DTDs?

Unusual, non-XML like syntax
No data typing, especially for element content
Limited extensibility
Only marginally compatible with namespaces
Cannot use mixed content and enforce order and number of child elements
Cannot enforce number of child elements without also enforcing order. (i.e. no & operator from SGML)
Confuses infoset augmentation with validation

What's Wrong with W3C XML Schema Language?

Complex, hard to understand
Not sufficiently extensible:
- Checksums
- SKUs match database
- sum of item prices equals total price
Poorly implemented
Confuses infoset annotation with validation

greeting.xml

<?xml version="1.0"?>
<GREETING>
Hello XML!
</GREETING>

greeting.rng

<?xml version="1.0"?>
<element name="GREETING" xmlns="http://relaxng.org/ns/structure/1.0">
  <text/>
</element>

Validating the document with Jing

$ jing greeting.rng greeting.xml

An Invalid Document

<?xml version="1.0"?>
<GREETING>
  <P>Hello XML!</P>
</GREETING>

Checking the Invalid Document

$ jing  greeting.rng greeting3.xml
/Users/elharo/Documents/speaking/sd2005west/relaxng/examples/greeting3.xml:
3:6: error: unknown element "P"

Notice how completely decoupled the validation is from the instance document. We can validate any document against any schema. We do not need to specify the schema in the instance document as you must do with DTDs and often need to do with W3C schemas.

RELAX NG Validators

Jing (Java): http://www.thaiopensource.com/relaxng/jing.html
libxml2 (C): http://xmlsoft.org/
Sun's Multischema Validator (Java): http://wwws.sun.com/software/xml/developers/multischema/
Tenuto (.NET): http://sourceforge.net/projects/relaxng

The compact syntax: greeting.rnc

element GREETING { text }

A More Complex Document

<?xml version="1.0"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

A More Complex Schema

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0">
  <element name="TITLE">
    <text/>
  </element>
  <element name="COMPOSER">
    <text/>
  </element>
  <element name="COMPOSER">
    <text/>
  </element>
  <element name="COMPOSER">
    <text/>
  </element>
  <element name="PRODUCER">
    <text/>
  </element>
  <element name="PUBLISHER">
     <text/>
  </element>
  <element name="LENGTH">
    <text/>
  </element>
  <element name="YEAR">
    <text/>
  </element>
  <element name="ARTIST">
    <text/>
  </element>
</element>

element SONG {
  element TITLE     { text },
  element COMPOSER  { text },
  element COMPOSER  { text },
  element COMPOSER  { text },
  element PRODUCER  { text },
  element PUBLISHER { text },
  element LENGTH    { text },
  element YEAR      { text },
  element ARTIST    { text }
}

Groups

zeroOrMore
oneOrMore
optional

A More Flexible Schema

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0">
  <element name="TITLE">
    <text/>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <text/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <text/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <text/>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <text/>
    </element>
  </oneOrMore>
</element>

element SONG {
  element TITLE     { text },
  element COMPOSER  { text }+,
  element PRODUCER  { text }*,
  element PUBLISHER { text }?,
  element LENGTH    { text }?,
  element YEAR      { text }?,
  element ARTIST    { text }+
}

A Couple of Notes

Boundary white space does not need to be declared

Element Content

<?xml version="1.0"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>
    <NAME>
      <GIVEN>Jacques</GIVEN>
      <FAMILY>Morali</FAMILY>
    </NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME>
      <GIVEN>Henri</GIVEN>
      <FAMILY>Belolo</FAMILY>
    </NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME>
      <GIVEN>Victor</GIVEN>
      <FAMILY>Willis</FAMILY>
    </NAME>
  </COMPOSER>
  <PRODUCER>
    <NAME>
      <GIVEN>Jacques</GIVEN>
      <FAMILY>Morali</FAMILY>
    </NAME>
  </PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

Nested structures

All of these structures can nest straight-forwardly

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0">
  <element name="TITLE">
    <text/>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <element name="NAME">
        <element name="GIVEN">
          <text/>
        </element>
        <element name="FAMILY">
          <text/>
        </element>
      </element>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <element name="NAME">
        <element name="GIVEN">
          <text/>
        </element>
        <element name="FAMILY">
          <text/>
        </element>
      </element>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <text/>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <text/>
    </element>
  </oneOrMore>
</element>

element SONG {
  element TITLE { text },
  element COMPOSER {
    element NAME {
      element GIVEN { text },
      element FAMILY { text }
    }
  }+,
  element PRODUCER {
    element NAME {
      element GIVEN { text },
      element FAMILY { text }
    }
  }*,
  element PUBLISHER { text }?,
  element LENGTH { text }?,
  element YEAR { text }?,
  element ARTIST { text }+
}

Sharing Content Models

PRODUCER and COMPOSER are really the same type.

<?xml version="1.0"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0">

  <start>
  
    <element name="SONG">
      <element name="TITLE">
        <text/>
      </element>
      
      <oneOrMore>
        <element name="COMPOSER">
          <ref name="personContent"/>
        </element>
      </oneOrMore>
      
      <zeroOrMore>
        <element name="PRODUCER">
          <ref name="personContent"/>
        </element>
      </zeroOrMore>
      
      <optional>
        <element name="PUBLISHER">
          <text/>
        </element>
      </optional>
      <optional>
        <element name="LENGTH">
          <text/>
        </element>
      </optional>
      <optional>
        <element name="YEAR">
          <text/>
        </element>
      </optional>
      <oneOrMore>
        <element name="ARTIST">
          <text/>
        </element>
      </oneOrMore>
    </element>
    
  </start>

  <define name="personContent">
    <element name="NAME">
      <element name="GIVEN">
        <text/>
      </element>
      <element name="FAMILY">
        <text/>
      </element>
    </element>
  </define>

</grammar>

start =
  element SONG {
    element TITLE     { text },
    element COMPOSER  { personContent }+,
    element PRODUCER  { personContent }*,
    element PUBLISHER { text }?,
    element LENGTH    { text }?,
    element YEAR      { text }?,
    element ARTIST    { text }+
  }
personContent =
  element NAME {
    element GIVEN  { text },
    element FAMILY { text }
  }

When Order Doesn't Matter

<?xml version="1.0"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <ARTIST>Village People</ARTIST>  
  <YEAR>1978</YEAR>
  <COMPOSER>
    <NAME><FAMILY>Morali</FAMILY> <GIVEN>Jacques</GIVEN></NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME><GIVEN>Henri</GIVEN> <FAMILY>Belolo</FAMILY></NAME>
  </COMPOSER>
  <PRODUCER>
    <NAME><GIVEN>Jacques</GIVEN> <FAMILY>Morali</FAMILY></NAME>
  </PRODUCER>
  <COMPOSER>
    <NAME><FAMILY>Willis</FAMILY> <GIVEN>Victor</GIVEN></NAME>
  </COMPOSER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
</SONG>

interleave

Much more powerful than either DTDs or schemas

<?xml version="1.0"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0">

  <start>
  
    <element name="SONG">
      <element name="TITLE">
        <text/>
      </element>
      <interleave>
          
          <oneOrMore>
            <element name="COMPOSER">
              <ref name="personContent"/>
            </element>
          </oneOrMore>
          
          <zeroOrMore>
            <element name="PRODUCER">
              <ref name="personContent"/>
            </element>
          </zeroOrMore>
          
          <optional>
            <element name="PUBLISHER">
              <text/>
            </element>
          </optional>
          <optional>
            <element name="LENGTH">
              <text/>
            </element>
          </optional>
          <optional>
            <element name="YEAR">
              <text/>
            </element>
          </optional>
          <oneOrMore>
            <element name="ARTIST">
              <text/>
            </element>
          </oneOrMore>
      </interleave>
    </element>
    
  </start>

  <define name="personContent">
    <element name="NAME">
      <interleave>
      <element name="GIVEN">
        <text/>
      </element>
      <element name="FAMILY">
        <text/>
      </element>
      </interleave>
    </element>
  </define>

</grammar>

start =
  element SONG {
    element TITLE        { text },
    (element COMPOSER    { personContent }+
     & element PRODUCER  { personContent }*
     & element PUBLISHER { text }?
     & element LENGTH    { text }?
     & element YEAR      { text }?
     & element ARTIST    { text }+)
  }
personContent =
  element NAME {
    element GIVEN    { text }
    & element FAMILY { text }
  }

Mixed Content

RELAX NG can enforce order and appearance of elements in mixed content.
Interleave with text element to validate mixed content

<?xml version="1.0"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>
    <NAME>Mr. <GIVEN>Jacques</GIVEN> <FAMILY>Morali</FAMILY> Esq.</NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME>Mr. <GIVEN>Henri</GIVEN> L. <FAMILY>Belolo</FAMILY>, M.D.</NAME>
  </COMPOSER>
  <COMPOSER>
    <NAME>Mr. <GIVEN>Victor</GIVEN> C. <FAMILY>Willis</FAMILY></NAME>
  </COMPOSER>
  <PRODUCER>
    <NAME>Mr. <GIVEN>Jacques</GIVEN> S. <FAMILY>Morali</FAMILY></NAME>
  </PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

Declaring Mixed Content

...
  <define name="personContent">
    <element name="NAME">
      <interleave>
        <text />
        <element name="GIVEN">
          <text/>
        </element>
        <element name="FAMILY">
          <text/>
        </element>
      </interleave>
    </element>
  </define>
...

personContent =
  element NAME {
    text
    & element GIVEN  { text }
    & element FAMILY { text }
  }

Choices

choice requires exactly one of a group of specified items to appear
Can be enclosed in optional, oneOrMore, or zeroOrMore

A song must have at least one of ARTIST, COMPOSER, or PRODUCER:

<?xml version="1.0"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0">

  <start>
  
    <element name="SONG">
      <element name="TITLE">
        <text/>
      </element>
          
      <oneOrMore>
        <choice>
          <element name="COMPOSER">
            <ref name="personContent"/>
          </element>
          <element name="PRODUCER">
            <ref name="personContent"/>
          </element>
          <element name="ARTIST">
            <text/>
          </element>
        </choice>
      </oneOrMore>
          
      <optional>
        <element name="PUBLISHER">
          <text/>
        </element>
      </optional>
      <optional>
        <element name="LENGTH">
          <text/>
        </element>
      </optional>
      <optional>
        <element name="YEAR">
          <text/>
        </element>
      </optional>
    </element>
    
  </start>

  <define name="personContent">
    <element name="NAME">
      <interleave>
      <element name="GIVEN">
        <text/>
      </element>
      <element name="FAMILY">
        <text/>
      </element>
      </interleave>
    </element>
  </define>

</grammar>

start =
  element SONG {
    element TITLE       { text },
    (element COMPOSER   { personContent }
     | element PRODUCER { personContent }
     | element ARTIST   { text })+,
    element PUBLISHER   { text }?,
    element LENGTH      { text }?,
    element YEAR        { text }?
  }
personContent =
  element NAME {
    element GIVEN    { text }
    & element FAMILY { text }
  }

Groups

group defines a model that can be used as a particle in other models
Like a sequence in W3C schemas or parentheses in DTDs

Allow a NAME element to contain either plain text or a GIVEN and a FAMILY but not both:

<element name="NAME>
  <choice>
    <text/>
    <group>
       <interleave>
         <element name="GIVEN">
           <text/>
         </element>
         <element name="FAMILY">
           <text/>
         </element>
       </interleave>
    </group>
  </choice>
</element>

A Document with Attributes

<?xml version="1.0"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <PHOTO ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

Declaring Attributes

attribute element
name attribute specifies the name of the attribute
optional element can make an attribute optional

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0">
  <element name="TITLE">
    <text/>
  </element>
  <element name="PHOTO">
    <attribute name="ALT">
      <text/>
    </attribute>
    <attribute name="WIDTH">
      <text/>
    </attribute>
    <attribute name="HEIGHT">
      <text/>
    </attribute>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <text/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <text/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <text/>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <text/>
    </element>
  </oneOrMore>
</element>

element SONG {
  element TITLE { text },
  element PHOTO {
    attribute ALT    { text },
    attribute WIDTH  { text },
    attribute HEIGHT { text }
  },
  element COMPOSER  { text }+,
  element PRODUCER  { text }*,
  element PUBLISHER { text }?,
  element LENGTH    { text }?,
  element YEAR      { text }?,
  element ARTIST    { text }+
}

Enumerations

List of all allowed values from which one must be chosen
A choice containing value elements

The publisher must be one of the oligopoly that controls 90% of U.S. music (Warner-Elektra-Atlantic, Universal Music Group, Sony Music Entertainment, Inc., Capitol Records, Inc., BMG Music)

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0">
  <element name="TITLE">
    <text/>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <text/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <text/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
    <choice>
      <value>Warner-Elektra-Atlantic</value>
      <value>Universal Music Group</value>
      <value>Sony Music Entertainment, Inc.</value>
      <value>Capitol Records, Inc.</value>
      <value>BMG Music</value>
    </choice>
  </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <text/>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <text/>
    </element>
  </oneOrMore>
</element>

element SONG {
  element TITLE    { text },
  element COMPOSER { text }+,
  element PRODUCER { text }*,
  element PUBLISHER {
    "Warner-Elektra-Atlantic"
    | "Universal Music Group"
    | "Sony Music Entertainment, Inc."
    | "Capitol Records, Inc."
    | "BMG Music"
  }?,
  element LENGTH { text }?,
  element YEAR   { text }?,
  element ARTIST { text }+
}

Namespaces

ns attribute specifies the namespace of the element it matches
Only applies in schema
Applies to that element element and its descendants
Until overridden
Validates solely based on URI; irrelevant whether instance document uses prefixes or not

Default Namespace

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<SONG xmlns="http://www.cafeconleche.org/namespace/song">
  <TITLE>Hot Cop</TITLE>
  <PHOTO ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

A Schema for a Document that uses Namespaces

<?xml version="1.0"?>
<element xmlns="http://relaxng.org/ns/structure/1.0"
         name="SONG" 
         ns="http://www.cafeconleche.org/namespace/song">
  <element name="TITLE">
    <text/>
  </element>
  <element name="PHOTO">
    <attribute name="ALT">
      <text/>
    </attribute>
    <attribute name="WIDTH">
      <text/>
    </attribute>
    <attribute name="HEIGHT">
      <text/>
    </attribute>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <text/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <text/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <text/>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <text/>
    </element>
  </oneOrMore>
</element>

default namespace = "http://www.cafeconleche.org/namespace/song"

element SONG {
  element TITLE { text },
  element PHOTO {
    attribute ALT    { text },
    attribute WIDTH  { text },
    attribute HEIGHT { text }
  },
  element COMPOSER  { text }+,
  element PRODUCER  { text }*,
  element PUBLISHER { text }?,
  element LENGTH    { text }?,
  element YEAR      { text }?,
  element ARTIST    { text }+
}

A Prefixed Schema for a Document that uses Namespaces

Can use prefixed names instead if you prefer
Usual namespace prefix binding attributes
Convenient in rare cases when namespaces shift from one element to the next (two widely intermixed vocabularies like XSLT)

<?xml version="1.0"?>
<element xmlns="http://relaxng.org/ns/structure/1.0"
         name="sng:SONG" 
         xmlns:sng="http://www.cafeconleche.org/namespace/song">
  <element name="sng:TITLE">
    <text/>
  </element>
  <element name="sng:PHOTO">
    <attribute name="ALT">
      <text/>
    </attribute>
    <attribute name="WIDTH">
      <text/>
    </attribute>
    <attribute name="HEIGHT">
      <text/>
    </attribute>
  </element>
  <oneOrMore>
    <element name="sng:COMPOSER">
      <text/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="sng:PRODUCER">
      <text/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="sng:PUBLISHER">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="sng:LENGTH">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="sng:YEAR">
      <text/>
    </element>
  </optional>
  <oneOrMore>
    <element name="sng:ARTIST">
      <text/>
    </element>
  </oneOrMore>
</element>

namespace sng = "http://www.cafeconleche.org/namespace/song"

element sng:SONG {
  element sng:TITLE { text },
  element sng:PHOTO {
    attribute ALT    { text },
    attribute WIDTH  { text },
    attribute HEIGHT { text }
  },
  element sng:COMPOSER  { text }+,
  element sng:PRODUCER  { text }*,
  element sng:PUBLISHER { text }?,
  element sng:LENGTH    { text }?,
  element sng:YEAR      { text }?,
  element sng:ARTIST    { text }+
}

Namespaces on Attributes

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<SONG xmlns="http://www.cafeconleche.org/namespace/song"
      xmlns:xlink="http://www.w3.org/1999/xlink">
  <TITLE>Hot Cop</TITLE>
  <PHOTO xlink:type="simple" xlink:href="hotcop.jpg"
         xlink:actuate="onLoad" xlink:show="embed"
    ALT="Victor Willis in Cop Outfit" WIDTH="100" HEIGHT="200"/>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
</SONG>

Attaching a namespace to an attribute

attribute element can have an ns attribute to specify the namespace
attribute element does not inherit ns attribute

<?xml version="1.0"?>
<element xmlns="http://relaxng.org/ns/structure/1.0"
         name="SONG" 
         ns="http://www.cafeconleche.org/namespace/song">
  <element name="TITLE">
    <text/>
  </element>
  <element name="PHOTO">
    <attribute name="ALT">
      <text/>
    </attribute>
    <attribute name="WIDTH">
      <text/>
    </attribute>
    <attribute name="HEIGHT">
      <text/>
    </attribute>
    <attribute name="type" ns="http://www.w3.org/1999/xlink">
      <text/>
    </attribute>
    <attribute name="href" ns="http://www.w3.org/1999/xlink">
      <text/>
    </attribute>
    <attribute name="actuate" ns="http://www.w3.org/1999/xlink">
      <text/>
    </attribute>
    <attribute name="show" ns="http://www.w3.org/1999/xlink">
      <text/>
    </attribute>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <text/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <text/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <text/>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <text/>
    </element>
  </oneOrMore>
</element>

default namespace = "http://www.cafeconleche.org/namespace/song"
namespace ns1 = "http://www.w3.org/1999/xlink"

element SONG {
  element TITLE { text },
  element PHOTO {
    attribute ALT    { text },
    attribute WIDTH  { text },
    attribute HEIGHT { text },
    
    attribute ns1:type    { text },
    attribute ns1:href    { text },
    attribute ns1:actuate { text },
    attribute ns1:show    { text }
  },
  element COMPOSER  { text }+,
  element PRODUCER  { text }*,
  element PUBLISHER { text }?,
  element LENGTH    { text }?,
  element YEAR      { text }?,
  element ARTIST    { text }+
}

Data Typing

Consider this document:

<foo>
    <value>45.67</value>
</foo>

What is the type of value?

Possible types

A longitude or latitude
A decimal monetary type, as in COBOL
A fixed point number
An infinitely precise floating point number such as represented by the java.math.BigDecimal class
An IEEE754 double
A Java double
An IEEE 754 float
A VAX Fortran REAL
An imprecisely known decimal number with 4 significant digits that's plus or minus 1 in the last place.
An imprecisely known decimal number with 4 significant digits that's plus or minus 5 in the last place.
Build 67 of version 45 of Microsoft Word
A regular expression matching all strings that begin with the two characters '4' and '5', followed by a single character, followed by the two characters '6' and '7'.
A string of characters a monkey typed on a keyboard

Other interpretations are doubtless possible, and even make sense in particular contexts. There's no guarantee that the string 45.67 in fact represents any particular type.

RELAX NG type libraries

RELAX NG defines no data types beyond text
But implementations are free to implement other type libraries
W3C XML Schema Data Types are commonly available
User defined type libraries

data element

data element replaces text element in content models

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <element name="TITLE">
    <text/>
  </element>
  <interleave>

    <oneOrMore>
      <element name="COMPOSER">
        <data type="string"/>
      </element>
    </oneOrMore>
    <zeroOrMore>
      <element name="PRODUCER">
        <data type="string"/>
      </element>
    </zeroOrMore>
    <oneOrMore>
      <element name="ARTIST">
        <data type="string"/>
      </element>
    </oneOrMore>
  
  <optional>
    <element name="PUBLISHER">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <data type="gYear" />
    </element>
  </optional>

  <element name="PRICE">
    <data type="string">
      <param name="pattern">\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?</param>
    </data>
  </element>
  </interleave>
</element>

namespace ns1 = "http://www.w3.org/1999/xhtml"

element SONG {
  element TITLE        { text },
  (element COMPOSER    { xsd:string }+
   & element PRODUCER  { xsd:string }*
   & element ARTIST    { xsd:string }+
   & element PUBLISHER { xsd:string }?
   & element LENGTH    { xsd:string }?
   & element YEAR      { xsd:gYear }?
   & element PRICE {
       xsd:string { pattern = "\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?" }
     })
}

Primitive Data Types for Schemas

Boolean
String
URIs
Numeric types
Time types
XML types

Numeric Data Types for Schemas

XML Schema Built-In Numeric Simple Types
Name	Type	Examples
float	IEEE 754 32-bit floating point number	-INF, -1E4, -0, 0, 12.78E-2, 12, INF, NaN
double	IEEE 754 64-bit floating point number	-INF, 1.401E-90, -1E4, -0, 0, 12.78E-2, 12, INF, NaN, 3.4E42
decimal	arbitrary precision, decimal numbers	-2.7E400, 5.7E-444, -3.1415292, 0, 7.8, 90200.76, 3.4E1024
integer	an arbitrarily large or small integer	-500000000000000000000000, -9223372036854775809, -126789, -1, 0, 1, 5, 23, 42, 126789, 9223372036854775808, 456734987324983264987362495809587095720978
nonPositiveInteger	an integer less than or equal to zero	0, -1, -2, -3, -4, -5, ...
negativeInteger	an integer strictly less than zero	-1, -2, -3, -4, -5, ...
long	an eight-byte two's complement integer such as Java's `long` type	-9223372036854775808, -12678967543233, -1, 9223372036854775807
int	an integer that can be represented as a four-byte, two's complement number such as Java's `int` type	-2147483648, -1, 0, 1, 5, 23, 42, 2147483647
short	an integer that can be represented as a two-byte, two's complement number such as Java's `short` type	-32768, -1, 0, 1, 5, 23, 42, 32767
byte	an integer that can be represented as a one-byte, two's complement number such as Java's `byte` type	-128, -1, 0, 1, 5, 23, 42, 127
nonNegativeInteger	an integer greater than or equal to zero	0, 1, 2, 3, 4, 5, ...
unsignedLong	an eight-byte unsigned integer	0, 1, 2, 3, 4, 5, ...18446744073709551614, 18446744073709551615
unsignedInt	a four-byte unsigned integer	0, 1, 2, 3, 4, 5, ...4294967294, 4294967295
unsignedShort	a two-byte unsigned integer	0, 1, 2, 3, 4, 5, ...65534, 65535
unsignedByte	a one-byte unsigned integer	0, 1, 2, 3, 4, 5, ...254, 255
positiveInteger	an integer strictly greater than zero	1, 2, 3, 4, 5, 6, ...

Time Data Types for Schemas

XML Schema Built-In Time Simple Types
Name	Type	Examples
dateTime	a particular moment in Coordinated Universal Time; up to an arbitrarily small fraction of a second	1999-05-31T13:20:00.000-05:00
gMonth	A given month in a given year	2000-10
gYear	a given year	2000
gMonthDay	a date in no particular year, or rather in every year	--10-31
gDay	a day in no particular month, or rather in every month	----31
duration	a length of time, without fixed endpoints, to an arbitrary fraction of a second	P2000Y10M31DT09H32M7.4312S
date	a specific day in history	2000-10-31
time	a specific time of day, that recurs every day	14:30:00.000, 09:30:00.000-05:00

XML Data Types for Schemas

XML Schema Built-In XML Simple Types
Name	Type	Examples
ID	XML 1.0 ID attribute type	any XML name that's unique among ID type attributes
IDREF	XML 1.0 IDREF attribute type	any XML name that's used as an ID type attribute elsewhere in the document
ENTITY	XML 1.0 ENTITY attribute type	any XML name that's declared as an unparsed entity in the DTD
NOTATION	????	????
language	Permissible values for `xml:lang` as defined in XML 1.0	en-GB, en-US, fr
IDREFS	XML 1.0 IDREFS attribute type	a white space separated list of IDREF names
ENTITIES	XML 1.0 ENTITIES attribute type	a white space separated list of ENTITY names
NMTOKEN	XML 1.0 NMTOKEN attribute type	12 are you ready
NMTOKENS	XML 1.0 NMTOKENS attribute type	a white space separated list of name tokens
Name	An XML 1.0 Name	set, title, rdf, math, math123, href
QName	an optionally prefixed, namespace qualified name	song:title
NCName	a local name without any colons	title

Assorted Data Types for Schemas

XML Schema Built-In Simple Types
Name	Type	Examples
string	Parsed Character Data; #PCDATA	Hot Cop
normalizedString	A string whose normalized value does not contain any tabs, carriage returns, or linefeeds	PIC1, PIC2, PIC3, cow_movie, MonaLisa, Hello World , Warhol, red green
token	A string whose normalized value has no leading or trailing white space, no tabs, no linefeeds, and not more than one consecutive space	p1 p2, ss123 45 6789, _92, red, green, NT Decl, seventeenp1, p2, 123 45 6789, ^&^&_92, red green blue, NT-Decl, seventeen; Mary had a little lamb, The love of money is the root of all Evil.
boolean	C++'s `bool` type	true, false, 1, 0
anyURI	relative or absolute URI	http://www.w3.org/TR/2000/WD-xmlschema-2-20000407/#duration, /javafaq/reports/JCE1.2.1.html
hexBinary	Arbitrary binary data encoded in hexadecimal form	A4E345EC54CC8D52198000FFEA6C
base64Binary	Arbitrary binary data encoded in Base64	6jKpNnmkkWeArsn5Oeeg2njcz+nXdk0f9kZI892ddlR8Lg1aMhPeFTYuoq3I6neFlb BjWzuktNZKiXYBfKsSTB8U09dTiJo2ir3HJuY7eW/p89osKMfixPQsp9vQMgzph6Qa lY7j4MB7y5ROJYsTr1/fFwmj/yhkHwpbpzed1LE=

Restricting types

param children of data specify the constraints on the type to create a subset of the normally accepted values
For example, this data element restricts a date to be any year from 1877 (the year Edison invented the phonograph) on:
```
<element name="YEAR">
  <data type="gYear">
    <param name="minInclusive">1877</param/>
  </data>
</element>
```
In the compact syntax:
element YEAR {xsd:gYear {minInclusive = "1877"}}

Facets

Facets include:
- length
- minLength
- maxLength
- pattern
- maxInclusive
- maxExclusive
- minInclusive
- minExclusive
- totalDigits
- fractionDigits
Not all facets apply to all types.
Facets not allowed/applicable in RELAX NG:
- enumeration
- whiteSpace

Length Facets: length, minLength, maxLength

The number of units allowed in a value
For strings (string, normalizedString, token, QName, NCname, ID, IDREF, language, anyURI, ENTITY, NOTATION, and NMTOKEN) the units are characters
For lists (IDREFS, ENTITIES, and NMTOKENS) the units are tokens
For binary types (hexBinary, base64Binary) the units are bytes after decoding
Must be a non-negative integer

For example, to say that all names and titles must contain between 1 and 255 characters:

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <element name="TITLE">
      <data type="string">
        <param name="minLength">1</param>
        <param name="maxLength">255</param>
      </data>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <data type="string">
        <param name="minLength">1</param>
        <param name="maxLength">255</param>
      </data>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <data type="string">
        <param name="minLength">1</param>
        <param name="maxLength">255</param>
      </data>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <data type="string">
        <param name="minLength">1</param>
        <param name="maxLength">255</param>
      </data>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <data type="gYear"/>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <data type="string"/>
    </element>
  </oneOrMore>
</element>

In compact syntax:

element SONG {
  element TITLE {
    xsd:string { minLength = "1" maxLength = "255" }
  },
  element COMPOSER {
    xsd:string { minLength = "1" maxLength = "255" }
  }+,
  element PRODUCER {
    xsd:string { minLength = "1" maxLength = "255" }
  }*,
  element PUBLISHER {
    xsd:string { minLength = "1" maxLength = "255" }
  }?,
  element LENGTH { xsd:string }?,
  element YEAR { xsd:gYear }?,
  element ARTIST { xsd:string }+
}

Facets for ordered items: minExclusive, maxExclusive, minInclusive, maxInclusive

Determines the minimum and maximum allowed values
Applies to ordered simple types including byte, unsignedByte, integer, positiveInteger, negativeInteger, nonNegativeInteger, nonPositiveInteger, int, unsignedInt, long, number, unsignedLong, short, unsignedShort, number, float, double, time, dateTime, duration, date, gMonth, gYear, gDay, and gMonthDay.

For example, to say that the year must be between 1877 and 2100:

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <element name="TITLE">
    <text/>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <data type="string"/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <data type="string"/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <data type="gYear">
        <param name="minInclusive">1877</param>
        <param name="maxInclusive">2100</param>
      </data>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <data type="string"/>
    </element>
  </oneOrMore>
</element>

In the compact syntax:

element SONG {
  element TITLE     { text },
  element COMPOSER  { xsd:string }+,
  element PRODUCER  { xsd:string }*,
  element PUBLISHER { xsd:string }?,
  element LENGTH    { xsd:string }?,
  element YEAR {
    xsd:gYear { minInclusive = "1877" 
                maxInclusive = "2100" 
              }
  }?,
  element ARTIST { xsd:string }+
}

Facets for decimal numbers: totalDigits and fractionDigits

totalDigits facet specifies the maximum number of decimal digits in a number as a positive integer
fractionDigits facet specifies the maximum number of decimal digits to the right of the decimal point as a non-negative integer
Applies to all types derived from decimal including byte, unsignedByte, integer, positiveInteger, negativeInteger, nonNegativeInteger, nonPositiveInteger, int, unsignedInt, long, unsignedLong, short, and unsignedShort.
Does not apply to float and double
You can specify at most two fractional digits or at most seven decimal digits, but not at least two fractional digits or exactly seven decimal digits

Adding a Price

<?xml version="1.0"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST>  
  <PRICE>$1.35</PRICE>  
</SONG>

The pattern facet

Suppose you want a money type to specify that the PRICE element content must look like $1.35 or ¥11000
Use the pattern facet to specify a regular expression instances must match

Regular Expressions

More or less Perl-like including the Unicode extensions introduced in Perl 5.6
The money regular expression:
\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?

\p{Sc}

Any Unicode currency indicator; e.g. $, ¥, £, ¤, etc.

\p{Nd}
A Unicode decimal digit character

\p{Nd}+
One or more Unicode decimal digit characters

\.
The period character

(\.\p{Nd}\p{Nd})
A string with a period followed by two decimal digits like .35

(\.\p{Nd}\p{Nd})?
Zero or one strings of the form .35

The Price Schema

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <element name="TITLE">
    <text/>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <data type="string"/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <data type="string"/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <data type="gYear" />
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <data type="string"/>
    </element>
  </oneOrMore>
  <element name="PRICE">
    <data type="string">
      <param name="pattern">\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?</param>
    </data>
  </element>
</element>

element SONG {
  element TITLE     { text },
  element COMPOSER  { xsd:string }+,
  element PRODUCER  { xsd:string }*,
  element PUBLISHER { xsd:string }?,
  element LENGTH    { xsd:string }?,
  element YEAR      { xsd:gYear }?,
  element ARTIST    { xsd:string }+,
  element PRICE {
    xsd:string { pattern = "\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?" }
  }
}

Lists

Matches a list of words separated by white space
Each word has a type
Can have multiple types

Allow multiple years in the YEAR element:

<element name="YEAR">
  <list>
    <oneOrMore>
      <data type="gYear"/>
    </oneOrMore>
  </list>
</element>

element SONG {
  element TITLE     { text },
  element COMPOSER  { xsd:string }+,
  element PRODUCER  { xsd:string }*,
  element PUBLISHER { xsd:string }?,
  element LENGTH    { xsd:string }?,
  element YEAR {
    list { xsd:gYear+ }
  }?,
  element ARTIST    { xsd:string }+
}

User defined type libraries

Available in Java (1.2 or later) and .NET
Implement the org.relaxng.datatype.DatatypeLibraryFactory interface

Prime Datatype

package com.elharo.xml.relaxng;

import org.relaxng.datatype.*;
import org.relaxng.datatype.helpers.StreamingValidatorImpl;

public class PrimeDatatype implements Datatype {

  private boolean isPrime(String literal) {
      
    try {
      int candidate = Integer.parseInt(literal); 
      if (candidate < 2) return false;
      double max = Math.sqrt(candidate);
      for (int i = 2; i <= max; i++) {
        if (candidate % i == 0) return false;
      }
      return true;
    }
    catch (NumberFormatException ex) {
      return false;      
    }
    
  }

  public boolean isValid(String literal, ValidationContext context) {
    return isPrime(literal);
  }

  public void checkValid(String literal, ValidationContext context) 
    throws DatatypeException {

    if (!isValid(literal, context)) {
      throw new DatatypeException(literal + " is not a prime number");
    }
    
  }

  
  public DatatypeStreamingValidator createStreamingValidator(ValidationContext context) {

    // Inefficient but simple. StreamingValidatorImpl stores 
    // everything in a string and then validates the string. More 
    // efficient implementations can validate piece by piece.
    return new StreamingValidatorImpl(this, context);

  }

  
  // These next three methods are closely tied together. The object
  // returned by this method si only used for sameValue and hashCode.
  public Object createValue(String literal, ValidationContext context) {

    if (isPrime(literal)) {
        return Integer.valueOf(literal);
    }
    return null;
    
  }
  
  public boolean sameValue(Object value1, Object value2) {

    if (value1 == null) return value2 == null;
    else return value1.equals(value2);
    
  }

  public int valueHashCode(Object value) {
    return value.hashCode();
  }

  public int getIdType() {
    return ID_TYPE_NULL;
  }

  public boolean isContextDependent() {
    return false;
  }
  
}

Prime Datatype Library

package com.elharo.xml.relaxng;

import org.relaxng.datatype.*;
import org.relaxng.datatype.helpers.*;

public class PrimeDatatypeLibrary implements DatatypeLibrary {

    public Datatype createDatatype(String typeLocalName)
      throws DatatypeException {
        
        if ("prime".equals(typeLocalName)) {
            return new PrimeDatatype();
        }
        throw new DatatypeException("Unsupported type: " + typeLocalName);
        
    }

    public DatatypeBuilder createDatatypeBuilder(String baseTypeLocalName) 
      throws DatatypeException {
        
        return new ParameterlessDatatypeBuilder(
          createDatatype("prime")
        );
        
    }

}

Prime Datatype Library Factory

package com.elharo.xml.relaxng;

import org.relaxng.datatype.*;

public class PrimeDatatypeLibraryFactory implements DatatypeLibraryFactory {

  public final static String namespace = "http://ns.cafeconleche.org/relaxng/primes";

  public DatatypeLibrary createDatatypeLibrary(String namespace) {
  
    if (PrimeDatatypeLibraryFactory.namespace.equals(namespace)) {
      return new PrimeDatatypeLibrary();
    }
    return null;
  
  }

}

Locating type libraries

Put the datatype library in a JAR archive
Include a META-INF/services/org.relaxng.datatype.DatatypeLibraryFactory file that contains the name of the class that implements the org.relaxng.datatype.DatatypeLibraryFactory interface
Add the .jar file to the CLASSPATH
Add the MSV/Jing .jar file to the CLASSPATH (Runnable archives don't work)

An invalid document

<?xml version="1.0"?>
<numbers>
  <number>2</number>
  <number>3</number>
  <number>4</number>
  <number>5</number>
  <number>6</number>
</numbers>

A Prime schema

<?xml version="1.0"?>
<element name="numbers" xmlns="http://relaxng.org/ns/structure/1.0">
  <oneOrMore>
    <element name="number">
      <data type="prime"
            datatypeLibrary="http://ns.cafeconleche.org/relaxng/primes"/>
    </element>
  </oneOrMore>
</element>

datatypes d = "http://ns.cafeconleche.org/relaxng/primes"

element numbers {
  element number { d:prime }+
}

include element

Breaks schema into multiple parts.

<!-- ==============================================================
      SVG12-RNG | SVG 1.2 Full Driver
     ============================================================== -->

<grammar ns='http://www.w3.org/2000/svg' xml:lang='en'
         xmlns='http://relaxng.org/ns/structure/1.0'
         xmlns:xlink='http://www.w3.org/1999/xlink'
         xmlns:a='http://relaxng.org/ns/compatibility/annotations/1.0'
         xmlns:svg='http://www.w3.org/2000/svg'
         datatypeLibrary='http://www.w3.org/2001/XMLSchema-datatypes'>



  <!-- ... common libraries and attributes ........................ -->
  <include href='../Tiny-1.2/datatypes.rng'/>
  <include href='../Tiny-1.2/core-attrib.rng'/>
  <include href='../Tiny-1.2/tiny-paint-attrib.rng'/>
  <include href='../Tiny-1.2/graphics-attrib.rng'/>
  <include href='../Tiny-1.2/transform-attrib.rng'/>
  <include href='../Tiny-1.2/xlink-attrib.rng'/>
  <include href='../Tiny-1.2/extresources-attrib.rng'/>
  <include href='../Tiny-1.2/media-attrib.rng'/>
  <include href='../Tiny-1.2/focusable-attrib.rng'/>
  <include href='../Tiny-1.2/editable-attrib.rng'/>
  <include href='../Tiny-1.2/backgroundfill-attrib.rng'/>
  <include href='opacity-attrib.rng'/>
  <include href='vectoreffects-attrib.rng'/>
  <include href='viewport-attrib.rng'/>


  <!-- ... element definitions .................................... -->
  <include href='structure.rng'/>
  <include href='../Tiny-1.2/conditional.rng'/>
  <include href='../Tiny-1.2/image.rng'/>
  <include href='../Tiny-1.2/shape.rng'/>
  <include href='text.rng'/>
  <include href='../Tiny-1.2/hyperlink.rng'/>
  <include href='../Tiny-1.2/script.rng'/>
  <include href='../Tiny-1.2/animation.rng'/>
  <include href='font.rng'/>
  <include href='../Tiny-1.2/extensibility.rng'/>
  <include href='gradient.rng'/>
  <include href='../Tiny-1.2/solidcolor.rng'/>
  <include href='../Tiny-1.2/audio.rng'/>
  <include href='../Tiny-1.2/video.rng'/>
  <include href='../Tiny-1.2/animation-element.rng'/>
  <include href='../Tiny-1.2/page.rng'/>
  <include href='flow.rng'/>
  <include href='../Tiny-1.2/handler.rng'/>
  <include href='../Tiny-1.2/prefetch.rng'/>

  <!-- ... only available in Full ................................. -->
  <include href='animevents-attrib.rng'/>
  <include href='docevents-attrib.rng'/>
  <include href='graphevents-attrib.rng'/>
  <include href='clip.rng'/>
  <include href='filter.rng'/>
  <include href='mask.rng'/>
  <include href='pattern.rng'/>
  <include href='style.rng'/>
  <include href='transition.rng'/>
  <include href='vectoreffects.rng'/>
  <include href='extendedlink.rng'/>
  <include href='cursor.rng'/>
  <include href='compositing-attrib.rng'/>
  <include href='marker.rng'/>
  <include href='profile.rng'/>
  <include href='shadow-attrib.rng'/>
  <include href='tooltip-attrib.rng'/>
  <include href='view.rng'/>
  <include href='xmlevents.rng'/>
  <include href='multiImage.rng'/>
  <include href='deviceColor.rng'/>
  <include href='traitDef.rng'/>

</grammar>

namespace a = "http://relaxng.org/ns/compatibility/annotations/1.0"
namespace svg = "http://www.w3.org/2000/svg"
namespace xlink = "http://www.w3.org/1999/xlink"

# ==============================================================
#  SVG12-RNG | SVG 1.2 Full Driver
# ==============================================================
[ xml:lang = "en" ]
grammar {
  # ... common libraries and attributes ........................
  include "datatypes.rnc" inherit = svg
  include "core-attrib.rnc" inherit = svg
  include "tiny-paint-attrib.rnc" inherit = svg
  include "graphics-attrib.rnc" inherit = svg
  include "transform-attrib.rnc" inherit = svg
  include "xlink-attrib.rnc" inherit = svg
  include "extresources-attrib.rnc" inherit = svg
  include "media-attrib.rnc" inherit = svg
  include "focusable-attrib.rnc" inherit = svg
  include "editable-attrib.rnc" inherit = svg
  include "backgroundfill-attrib.rnc" inherit = svg
  include "opacity-attrib.rnc" inherit = svg
  include "vectoreffects-attrib.rnc" inherit = svg
  include "viewport-attrib.rnc" inherit = svg
  # ... element definitions ....................................
  include "structure.rnc" inherit = svg
  include "conditional.rnc" inherit = svg
  include "image.rnc" inherit = svg
  include "shape.rnc" inherit = svg
  include "text.rnc" inherit = svg
  include "hyperlink.rnc" inherit = svg
  include "script.rnc" inherit = svg
  include "animation.rnc" inherit = svg
  include "font.rnc" inherit = svg
  include "extensibility.rnc" inherit = svg
  include "gradient.rnc" inherit = svg
  include "solidcolor.rnc" inherit = svg
  include "audio.rnc" inherit = svg
  include "video.rnc" inherit = svg
  include "animation-element.rnc" inherit = svg
  include "page.rnc" inherit = svg
  include "flow.rnc" inherit = svg
  include "handler.rnc" inherit = svg
  include "prefetch.rnc" inherit = svg
  # ... only available in Full .................................
  include "animevents-attrib.rnc" inherit = svg
  include "docevents-attrib.rnc" inherit = svg
  include "graphevents-attrib.rnc" inherit = svg
  include "clip.rnc" inherit = svg
  include "filter.rnc" inherit = svg
  include "mask.rnc" inherit = svg
  include "pattern.rnc" inherit = svg
  include "style.rnc" inherit = svg
  include "transition.rnc" inherit = svg
  include "vectoreffects.rnc" inherit = svg
  include "extendedlink.rnc" inherit = svg
  include "cursor.rnc" inherit = svg
  include "compositing-attrib.rnc" inherit = svg
  include "marker.rnc" inherit = svg
  include "profile.rnc" inherit = svg
  include "shadow-attrib.rnc" inherit = svg
  include "tooltip-attrib.rnc" inherit = svg
  include "view.rnc" inherit = svg
  include "xmlevents.rnc" inherit = svg
  include "multiImage.rnc" inherit = svg
  include "deviceColor.rnc" inherit = svg
  include "traitDef.rnc" inherit = svg
}

externalref element

Matches any pattern defined in an external schema
href attribute points to the external schema

<?xml version="1.0"?>
<SONG>
  <TITLE>Hot Cop</TITLE>
  <COMPOSER>Jacques Morali</COMPOSER>
  <COMPOSER>Henri Belolo</COMPOSER>
  <COMPOSER>Victor Willis</COMPOSER>
  <PRODUCER>Jacques Morali</PRODUCER>
  <PUBLISHER>PolyGram Records</PUBLISHER>
  <LENGTH>6:20</LENGTH>
  <YEAR>1978</YEAR>
  <ARTIST>Village People</ARTIST> 
  <DESCRIPTION>
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head>
      <title>The schema requires this</title>
    </head>
    <body>
    <p>
      A catchy little ditty that never achieved the
      success of <cite>YMCA</cite> or <cite>In the Navy</cite>.
    </p>
    </body>
    </html>
  </DESCRIPTION>
</SONG>

Pointing to the XHTML schema

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0">
  <element name="TITLE">
    <text/>
  </element>
  <oneOrMore>
    <element name="COMPOSER">
      <text/>
    </element>
  </oneOrMore>
  <zeroOrMore>
    <element name="PRODUCER">
      <text/>
    </element>
  </zeroOrMore>
  <optional>
    <element name="PUBLISHER">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <text/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <text/>
    </element>
  </optional>
  <oneOrMore>
    <element name="ARTIST">
      <text/>
    </element>
  </oneOrMore>
  <optional>
    <element name="DESCRIPTION">
      <externalRef href="http://thaiopensource.com/relaxng/xhtml/xhtml-basic.rng"/>
    </element>
  </optional>
</element>

element SONG {
  element TITLE       { text },
  element COMPOSER    { text }+,
  element PRODUCER    { text }*,
  element PUBLISHER   { text }?,
  element LENGTH      { text }?,
  element YEAR        { text }?,
  element ARTIST      { text }+,
  element DESCRIPTION { external "xhtml-basic.rnc" }?
}

Annotations

All elements/attributes from namespaces other than http://relaxng.org/ns/structure/1.0 are ignored
Annotate with XHTML, Schematron or any other namespaced vocabulary
Use RELAX NG div element to group multiple elements in a grammar together with a single annotation

<?xml version="1.0"?>
<element name="SONG" xmlns="http://relaxng.org/ns/structure/1.0"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <element name="TITLE">
    <text/>
  </element>
  <interleave>

    <oneOrMore>
      <element name="COMPOSER">
        <data type="string"/>
      </element>
    </oneOrMore>
    <zeroOrMore>
      <element name="PRODUCER">
        <data type="string"/>
      </element>
    </zeroOrMore>
    <oneOrMore>
      <element name="ARTIST">
        <data type="string"/>
      </element>
    </oneOrMore>
  
  <optional>
    <element name="PUBLISHER">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="LENGTH">
      <data type="string"/>
    </element>
  </optional>
  <optional>
    <element name="YEAR">
      <data type="gYear" />
    </element>
  </optional>

  <element name="PRICE">
    <data type="string">
      <param name="pattern">\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?</param>
    </data>
  </element>
  </interleave>
</element>

namespace ns1 = "http://www.w3.org/1999/xhtml"

element SONG {
  element TITLE        { text },
  (element COMPOSER    { xsd:string }+
   & element PRODUCER  { xsd:string }*
   & element ARTIST    { xsd:string }+
   & element PUBLISHER { xsd:string }?
   & element LENGTH    { xsd:string }?
   & element YEAR      { xsd:gYear }?
   & element PRICE {
       xsd:string { pattern = "\p{Sc}\p{Nd}+(\.\p{Nd}\p{Nd})?" }
     })
}

RELAX NG in Java 1.5/JAXP 1.3

Not bundled; must install third party library

import javax.xml.*;
import javax.xml.validation.*;
import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;
import java.io.*;
import org.xml.sax.*;

public class Relax implements ErrorHandler {

  public static void main(String[] args) {
  
    if (args.length < 2) {
      System.out.println("Usage: java Relax schema.rng file.xml");
      return;
    }
    
    Schema schema;
    try {
      SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.RELAXNG_NS_URI);
      schema = factory.newSchema(new File(args[1]));
    }
    catch (SAXException ex) {
      System.out.println("Schema error in " + args[0]);  
      System.out.println(ex.getMessage());
      return;
    }
    catch (IllegalArgumentException ex) {
      System.out.println("This implementation does not support RELAX NG.");
      return;
    }
    Validator validator = schema.newValidator();
    Source source = new StreamSource(new File(args[1]));
    validator.setErrorHandler(new Relax());
    try {
      validator.validate(source);
    }
    catch (SAXException ex) {
      System.out.println(args[1] + " is not well-formed.");  
      System.out.println(ex.getMessage());
    }
    catch (IOException ex) {
      System.out.println("Could not validate " + args[1] + " due to an I/O error.");  
      System.out.println(ex.getMessage());
    }
    
  }
  
  public void warning(SAXParseException exception) {
    
    System.out.println("Warning: " + exception.getMessage());
    System.out.println(" at line " + exception.getLineNumber() 
     + ", column " + exception.getColumnNumber());
    
  }
  
  public void error(SAXParseException exception) {
     
    System.out.println("Error: " + exception.getMessage());
    System.out.println(" at line " + exception.getLineNumber() 
     + ", column " + exception.getColumnNumber());
    
  }
  
  public void fatalError(SAXParseException exception) {
     
    System.out.println("Fatal Error: " + exception.getMessage());
    System.out.println(" at line " + exception.getLineNumber() 
     + ", column " + exception.getColumnNumber());
     
  }

}

Other features

Wild cards with anyName and nsName
Exclusions with except
Redefining external content models when importing
Attribute or child element

What RELAX NG doesn't do

Cannot declare entities
Parent models
Extra-document validation
ID-IDREF/key-keyref^*
PSVI

^* Can be added

RELAX NG is being used for

Trang

Converts between:
- RELAX XML syntax
- RELAX Compact syntax
- DTDs
- W3C XML Schema Language

$ trang http://www.w3.org/Graphics/SVG/1.2/rng/Full-1.2/Full-1.2.rng full.xsd
http://www.w3.org/Graphics/SVG/1.2/rng/Tiny-1.2/tiny-structure.rng:401:13: warning: choice between attributes and children cannot be represented; approximating
http://www.w3.org/Graphics/SVG/1.2/rng/Tiny-1.2/tiny-structure.rng:420:13: warning: choice between attributes and children cannot be represented; approximating
http://www.w3.org/Graphics/SVG/1.2/rng/Tiny-1.2/tiny-structure.rng:438:13: warning: choice between attributes and children cannot be represented; approximating
http://www.w3.org/Graphics/SVG/1.2/rng/Full-1.2/structure.rng:24:13: warning: choice between attributes and children cannot be represented; approximating
http://www.w3.org/Graphics/SVG/1.2/rng/Tiny-1.2/script.rng:38:13: warning: choice between attributes and children cannot be represented; approximating
http://www.w3.org/Graphics/SVG/1.2/rng/Tiny-1.2/tiny-flow.rng:22:15: warning: cannot represent an optional group of attributes; approximating
http://www.w3.org/Graphics/SVG/1.2/rng/Tiny-1.2/handler.rng:44:13: warning: choice between attributes and children cannot be represented; approximating
http://www.w3.org/Graphics/SVG/1.2/rng/Full-1.2/style.rng:81:13: warning: choice between attributes and children cannot be represented; approximating

To Learn More

RELAX NG
- Eric van der Vlist
- O'Reilly & Associates, 2004
- ISBN 0-596-00421-4
- http://books.xmlschemata.org/relaxng/
This presentation: http://www.cafeconleche.org/slides/sd2007west/relaxng/
RELAX NG Tutorial: http://www.oasis-open.org/committees/relax-ng/tutorial.html

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