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Generating Schemas with Relaxer

To start off, you will walk through a few simple examples of generating schemas with Relaxer. Example documents mentioned in this tutorial are available in a ZIP archive at http://www.relaxer.org/doc/tutorial/tutorial.zip. Now consider the following XML document, date.xml:

date.xml
<?xml version="1.0"?>

<instant>
 <date type="ISO8601">
  <year>2003</year>
  <month>01</month>
  <day>01</day>
 </date>
</instant>

This simple, well-formed XML document uses a hierarchy of elements to represent an ISO 8601 date.

Creating a DTD

You can create a document type definition or DTD for date.xml by issuing the following command:

C:\Relaxer>relaxer -verbose -dtd date.xml

The -verbose switch (which is not required) allows you to see some detail about Relaxer's output:

Copyright(c) 2000-2003 ASAMI,Tomoharu. All rights reserved.
Relaxer Version 1.0RCb (20030115) by asami@relaxer.org
Source file     : file:/C:/Relaxer/date.xml
        artifact = date.dtd

The command produces the file date.dtd, seen here:

date.dtd
<!-- Generated by Relaxer 1.0RCb -->
<!-- Fri Jan 17 10:14:16 PST 2003 -->

<!ELEMENT date (year, month, day)>
<!ATTLIST date type CDATA #REQUIRED>

<!ELEMENT year (#PCDATA)>

<!ELEMENT day (#PCDATA)>

<!ELEMENT instant (date)>

<!ELEMENT month (#PCDATA)>

This result represents only one possible DTD for date.xml. Relaxer guesses at a feasible structure for a valid XML document based on the content of the document date.xml. For example, Relaxer supposes that the type attribute on the <date> element is required. If there were multiple instances of the <date> element, and type occurred on only one of those instances, Relaxer would guess that the attribute was optional (#IMPLIED).

You can also generate a DTD based on two or more instances. Relaxer examines the instances and decides on a best-fit DTD for them. Here is another document that is similar to date.xml but has a different content model. It is called time.xml:

time.xml
<?xml version="1.0" encoding="UTF-8"?>

<instant>
 <time>
  <hour>11</hour>
  <minute>33</minute>
  <second>14</second>
  <utc zone="GMT"/>
 </time>
</instant>

If you want Relaxer to consider the content models of both documents, you can type this command:

C:\Relaxer>relaxer -verbose -dtd time.xml date.xml

This creates the DTD time.dtd:

time.dtd
<!-- Generated by Relaxer 1.0RCb -->
<!-- Fri Jan 17 10:18:05 PST 2003 -->

<!ELEMENT date (year, month, day)>
<!ATTLIST date type CDATA #REQUIRED>

<!ELEMENT year (#PCDATA)>

<!ELEMENT time (hour, minute, second, utc)>

<!ELEMENT day (#PCDATA)>

<!ELEMENT utc EMPTY>
<!ATTLIST utc zone CDATA #REQUIRED>

<!ELEMENT second (#PCDATA)>

<!ELEMENT minute (#PCDATA)>

<!ELEMENT hour (#PCDATA)>

<!ELEMENT instant (date | time)>

<!ELEMENT month (#PCDATA)>

Notice how the content model for <instant> allows for a choice of either a <date> or a <time> child.

In addition to DTDs, it is possible to generate other schemas with Relaxer, such as Relax Core, RELAX NG, and XML Schema.

Generating Relax Core Schema

To create a Relax Core schema, use the following command (note the -rxm switch):

C:\Relaxer>relaxer -verbose -rxm date.xml

This produces the file date.rxm shown here:

date.rxm
<?xml version="1.0" encoding="UTF-8" ?>
<module xmlns="http://www.xml.gr.jp/xmlns/relaxCore" relaxCoreVersion="1.0" \
    targetNamespace="">
  <interface>
    <export label="instant"/>
  </interface>
  <elementRule label="instant">
    <tag name="instant"/>
    <sequence>
      <ref label="date"/>
    </sequence>
  </elementRule>
  <elementRule label="date">
    <tag name="date">
      <attribute name="type" type="token"/>
    </tag>
    <sequence>
      <element name="year" type="int"/>
      <element name="month" type="int"/>
      <element name="day" type="int"/>
    </sequence>
  </elementRule>
</module>

To generate a schema for both time.xml and date.xml, type the following command line:

C:\Relaxer>relaxer -verbose -rxm time.xml date.xml

The artifact produced by this command is time.rxm:

time.rxm
<?xml version="1.0" encoding="UTF-8" ?>
<module xmlns="http://www.xml.gr.jp/xmlns/relaxCore" relaxCoreVersion="1.0" \
    targetNamespace="">
  <interface>
    <export label="instant"/>
  </interface>
  <elementRule label="instant">
    <tag name="instant"/>
    <sequence>
      <choice>
        <ref label="time"/>
        <ref label="date"/>
      </choice>
    </sequence>
  </elementRule>
  <elementRule label="time">
    <tag name="time"/>
    <sequence>
      <element name="hour" type="int"/>
      <element name="minute" type="int"/>
      <element name="second" type="int"/>
      <ref label="utc"/>
    </sequence>
  </elementRule>
  <elementRule label="utc">
    <tag name="utc">
      <attribute name="zone" type="token"/>
    </tag>
    <empty/>
  </elementRule>
  <elementRule label="date">
    <tag name="date">
      <attribute name="type" type="token"/>
    </tag>
    <sequence>
      <element name="year" type="int"/>
      <element name="month" type="int"/>
      <element name="day" type="int"/>
    </sequence>
  </elementRule>
</module>

Now you'll generate schemas for RELAX NG.

Generating RELAX NG Schemas

To create a RELAX NG schema, try the following (note the -rng switch):

C:\Relaxer>relaxer -verbose -rng date.xml

The result is the file date.rng shown here:

date.rng
<?xml version="1.0" encoding="UTF-8" ?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0" \
    datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <start>
    <ref name="instant"/>
  </start>
  <define name="instant">
    <element name="instant">
      <ref name="date"/>
    </element>
  </define>
  <define name="date">
    <element name="date">
      <attribute name="type">
        <data type="token"/>
      </attribute>
      <element name="year">
        <data type="int"/>
      </element>
      <element name="month">
        <data type="int"/>
      </element>
      <element name="day">
        <data type="int"/>
      </element>
    </element>
  </define>
</grammar>

To generate a RELAX NG schema for both time.xml and date.xml, use this command:

C:\Relaxer>relaxer -verbose -rng time.xml date.xml

The file produced by this command is time.rng:

time.rng
<?xml version="1.0" encoding="UTF-8" ?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0" \
    datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
  <start>
    <ref name="instant"/>
  </start>
  <define name="instant">
    <element name="instant">
      <choice>
        <ref name="time"/>
        <ref name="date"/>
      </choice>
    </element>
  </define>
  <define name="time">
    <element name="time">
      <element name="hour">
        <data type="int"/>
      </element>
      <element name="minute">
        <data type="int"/>
      </element>
      <element name="second">
        <data type="int"/>
      </element>
      <ref name="utc"/>
    </element>
  </define>
  <define name="utc">
    <element name="utc">
      <attribute name="zone">
        <data type="token"/>
      </attribute>
    </element>
  </define>
  <define name="date">
    <element name="date">
      <attribute name="type">
        <data type="token"/>
      </attribute>
      <element name="year">
        <data type="int"/>
      </element>
      <element name="month">
        <data type="int"/>
      </element>
      <element name="day">
        <data type="int"/>
      </element>
    </element>
  </define>
</grammar>

Finally, you will create schemas in the W3C XML Schema Description Language (XSD).

Generating Schemas in XML Schema

For XML Schema, use the -xsd switch:

C:\Relaxer>relaxer -verbose -xsd date.xml

The file this command produces is date.xsd, shown here:

date.xsd
<?xml version="1.0" encoding="UTF-8" ?>
<xsd:schema xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="instant" type="instant"/>
  <xsd:complexType name="instant">
    <xsd:sequence>
      <xsd:element name="date" type="date"/>
    </xsd:sequence>
  </xsd:complexType>
  <xsd:complexType name="date">
    <xsd:sequence>
      <xsd:element name="year" type="xsd:int"/>
      <xsd:element name="month" type="xsd:int"/>
      <xsd:element name="day" type="xsd:int"/>
    </xsd:sequence>
    <xsd:attribute name="type" type="xsd:token"/>
  </xsd:complexType>
</xsd:schema>

To generate an XSD schema for both time.xml and date.xml, do the following:

C:\Relaxer>relaxer -verbose -xsd time.xml date.xml

This creates time.xsd:

time.xsd
<?xml version="1.0" encoding="UTF-8" ?>
<xsd:schema xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="instant" type="instant"/>
  <xsd:complexType name="instant">
    <xsd:sequence>
      <xsd:choice>
        <xsd:element name="time" type="time"/>
        <xsd:element name="date" type="date"/>
      </xsd:choice>
    </xsd:sequence>
  </xsd:complexType>
  <xsd:complexType name="time">
    <xsd:sequence>
      <xsd:element name="hour" type="xsd:int"/>
      <xsd:element name="minute" type="xsd:int"/>
      <xsd:element name="second" type="xsd:int"/>
      <xsd:element name="utc" type="utc"/>
    </xsd:sequence>
  </xsd:complexType>
  <xsd:complexType name="utc">
    <xsd:sequence/>
    <xsd:attribute name="zone" type="xsd:token"/>
  </xsd:complexType>
  <xsd:complexType name="date">
    <xsd:sequence>
      <xsd:element name="year" type="xsd:int"/>
      <xsd:element name="month" type="xsd:int"/>
      <xsd:element name="day" type="xsd:int"/>
    </xsd:sequence>
    <xsd:attribute name="type" type="xsd:token"/>
  </xsd:complexType>
</xsd:schema>

Next, you will learn how to generate Java code with Relaxer.

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