RELAX NG

• RELAX NG (Regular Language description for XML Next Generation) (.rng)
• Easier to implement and learn than XSD
• Can be combined with XML Datatype Schema

• Has both an XML syntax and a compact non-XML syntax
• Supports XML namespaces

Syntax

Default namespace

<?xml version="1.0" encoding="UTF-8"?>
<element name="root-element-name"
         xmlns="http://relaxng.org/ns/structure/1.0">
  <element name="element-name">
    ...
  </element>
</element>

Specified namespace

<?xml version="1.0" encoding="UTF-8"?>
<rng:element name="root-element-name"
             xmlns:rng="http://relaxng.org/ns/structure/1.0">
  <rng:element name="element-name">
    ...
  </rng:element>
</rng:element>

Datatypes

<element name="root-element-name"
         xmlns:rng="http://relaxng.org/ns/structure/1.0"
         datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <element name="element-name">
    <data type="type-name"/>
  </element>
  ...
</element>

Grammar

<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0">
<start>
  ...
</start>
<define>
  ...
</define>
  ...
</grammar>

References

<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0">
<start>
  <ref name="Ref-Name"/>
</start>
<define name="Ref-Name">
  <element name="element-name">
    ..
  </element>
</define>
...
</grammar>

Sample RELAX NG files

Default namespace

<?xml version="1.0" encoding="UTF-8"?>
<element name="catalog"
         xmlns="http://relaxng.org/ns/structure/1.0">
  <zeroOrMore>
    <element name="cd">
      <element name="title"><text/></element>
      <element name="artist"><text/></element>
    </element>
  </zeroOrMore>
</element>

Specified namespace

<?xml version="1.0" encoding="UTF-8"?>
<rng:element name="catalog"
             xmlns:rng="http://relaxng.org/ns/structure/1.0">
  <rng:zeroOrMore>
    <rng:element name="cd">
      <rng:element name="title"><rng:text/></rng:element>
      <rng:element name="artist"><rng:text/></rng:element>
    </rng:element>
  </rng:zeroOrMore>
</rng:element>

Datatypes

<element name="point"
         xmlns:rng="http://relaxng.org/ns/structure/1.0"
         datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <element name="x">
    <data type="double"/>
  </element>
  <element name="y">
    <data type="double"/>
  </element>
</element>

Grammar

<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0">
<start>
  ...
</start>
<define>
  ...
</define>
...
</grammar>

References

<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0">
<start>
  <ref name="Catalog"/>
</start>
<define name="Catalog">
  <element name="catalog">
    <zeroOrMore>
      <ref name="CD"/>
    </zeroOrMore>
  </element>
</define>
<define name="CD">
  <element name="cd">
    <ref name="Title"/>
    <ref name="Artist"/>
  </element>
</define>
<define name="Title">
  <element name="title">
    <text/>
  </element>
</define>
<define name="Artist">
  <element name="artist">
    <text/>
  </element>
</define>
</grammar>

Sample usage in XML files

<?xml version="1.0" encoding="UTF-8"?>
<catalog>
  <cd>
    <title>...</title>
    <artist>...</artist>
  </cd>
  ...
</catalog>