Systems Biology Markup Language XML Schema
From: http://www.cds.caltech.edu/erato/sbml-level-1/sbml-level-1.html

B. XML Schema for SBML 

The following is an XML Schema definition for the Systems Biology Markup Language. Example applications of this XML Schema are
presented in Section 5. 


<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2000/10/XMLSchema">
  <xsd:annotation>
    <xsd:documentation> 
      File name : sbml.xsd
      Author : Daniel Lucio, James Schaff, Andrew Finney, Michael Hucka
      Description : XML Schema for the Systems Biology Markup Language
      Organization: Caltech ERATO Kitano
      Version : 1
      Modified : 2001-03-02 22:29 PST
    </xsd:documentation>
  </xsd:annotation>
  <!-- SName -->
  <xsd:simpleType name="SName">
    <xsd:annotation>
      <xsd:documentation>
         SName type used for expressing
         names of components in a model
      </xsd:documentation>
    </xsd:annotation>
    <xsd:restriction base="xsd:string">
      <xsd:pattern value="(_|[a-z]|[A-Z])(_|[a-z]|[A-Z]|[0-9])*"/>
    </xsd:restriction>
  </xsd:simpleType>
  <!-- SBase -->
  <xsd:complexType name="SBase" abstract="true">
    <xsd:annotation>
      <xsd:documentation>
        Designed to allow a modeler or a pacckage to attach
        information to each component.
      </xsd:documentation>
    </xsd:annotation>
    <xsd:sequence>
      <xsd:element name="notes" minOccurs="0">
        <xsd:complexType>
          <xsd:sequence>
            <xsd:any namespace="http://www.w3.org/1999/xhtml"
                     processContents="skip" maxOccurs="unbounded"/>
          </xsd:sequence>
        </xsd:complexType>
      </xsd:element>
      <xsd:element name="annotations" minOccurs="0">
        <xsd:complexType>
          <xsd:sequence>
            <xsd:any processContents="skip" maxOccurs="unbounded"/>
          </xsd:sequence>
        </xsd:complexType>
      </xsd:element>
    </xsd:sequence>
  </xsd:complexType>
  <!-- LisOfParameter  -->
  <xsd:element name="listOfParameters">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:element name="parameter" type="Parameter"
                     maxOccurs="unbounded"/>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>
  <!-- Model -->
  <xsd:complexType name="Model">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:sequence>
          <xsd:element name="listOfUnitDefinitions" minOccurs="0">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="unitDefinition" type="UnitDefinition"
                             maxOccurs="unbounded"/>
              </xsd:sequence>
            </xsd:complexType>
          </xsd:element>
          <xsd:element name="listOfCompartments">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="compartment" type="Compartment" maxOccurs="unbounded"/>
              </xsd:sequence>
            </xsd:complexType>
          </xsd:element>
          <xsd:element name="listOfSpecies">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="specie" type="Specie" maxOccurs="unbounded"/>
              </xsd:sequence>
            </xsd:complexType>
          </xsd:element>
          <xsd:element ref="listOfParameters" minOccurs="0"/>
          <xsd:element name="listOfRules" minOccurs="0">
            <xsd:complexType>
              <xsd:choice maxOccurs="unbounded">
                <xsd:element name="algebraicRule" type="AlgebraicRule" minOccurs="0"/>
                <xsd:element name="compartmentVolumeRule" type="CompartmentVolumeRule"
                             minOccurs="0"/>
                <xsd:element name="specieConcentrationRule" type="SpecieConcentrationRule" 
                             minOccurs="0"/>
                <xsd:element name="parameterRule" type="ParameterRule" minOccurs="0"/>
              </xsd:choice>
            </xsd:complexType>
          </xsd:element>
          <xsd:element name="listOfReactions">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="reaction" type="Reaction" maxOccurs="unbounded"/>
              </xsd:sequence>
            </xsd:complexType>
          </xsd:element>
        </xsd:sequence>
        <xsd:attribute name="name" type="SName" use="optional"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <!-- UnitDefinition -->
  <xsd:complexType name="UnitDefinition">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:sequence>
          <xsd:element name="listOfUnits" minOccurs="0">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="unit" type="Unit" maxOccurs="unbounded"/>
              </xsd:sequence>
            </xsd:complexType>
          </xsd:element>
        </xsd:sequence>
        <xsd:attribute name="name" type="SName" use="required"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <!-- Compartment -->
  <xsd:complexType name="Compartment">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:attribute name="name" type="SName" use="required"/>
        <xsd:attribute name="volume" type="xsd:double" use="default" value="1"/>
        <xsd:attribute name="units" type="SName" use="optional"/>
        <xsd:attribute name="outside" type="SName" use="optional"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <!-- Specie -->
  <xsd:complexType name="Specie">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:attribute name="name" type="SName" use="required"/>
        <xsd:attribute name="compartment" type="SName" use="required"/>
        <xsd:attribute name="initialAmount" type="xsd:double" use="required"/>
        <xsd:attribute name="units" type="SName" use="optional"/>
        <xsd:attribute name="boundaryCondition" type="xsd:boolean" 
                       use="default" value="false"/>
        <xsd:attribute name="charge" type="xsd:integer" use="optional"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <!-- Parameter -->
  <xsd:complexType name="Parameter">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:attribute name="name" type="SName" use="required"/>
        <xsd:attribute name="value" type="xsd:double" use="required"/>
        <xsd:attribute name="units" type="SName" use="optional"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <!-- UnitKind -->
  <xsd:simpleType name="UnitKind">
    <xsd:restriction base="xsd:string">
      <xsd:enumeration value="ampere"/>
      <xsd:enumeration value="becquerel"/>
      <xsd:enumeration value="candela"/>
      <xsd:enumeration value="celsius"/>
      <xsd:enumeration value="coulomb"/>
      <xsd:enumeration value="dimensionless"/>
      <xsd:enumeration value="farad"/>
      <xsd:enumeration value="gram"/>
      <xsd:enumeration value="gray"/>
      <xsd:enumeration value="henry"/>
      <xsd:enumeration value="hertz"/>
      <xsd:enumeration value="item"/>
      <xsd:enumeration value="joule"/>
      <xsd:enumeration value="katal"/>
      <xsd:enumeration value="kelvin"/>
      <xsd:enumeration value="kilogram"/>
      <xsd:enumeration value="liter"/>
      <xsd:enumeration value="litre"/>
      <xsd:enumeration value="lumen"/>
      <xsd:enumeration value="lux"/>
      <xsd:enumeration value="meter"/>
      <xsd:enumeration value="metre"/>
      <xsd:enumeration value="mole"/>
      <xsd:enumeration value="newton"/>
      <xsd:enumeration value="ohm"/>
      <xsd:enumeration value="pascal"/>
      <xsd:enumeration value="radian"/>
      <xsd:enumeration value="second"/>
      <xsd:enumeration value="siemens"/>
      <xsd:enumeration value="sievert"/>
      <xsd:enumeration value="steradian"/>
      <xsd:enumeration value="tesla"/>
      <xsd:enumeration value="volt"/>
      <xsd:enumeration value="watt"/>
      <xsd:enumeration value="weber"/>
    </xsd:restriction>
  </xsd:simpleType>
  <!-- Unit -->
  <xsd:complexType name="Unit">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:attribute name="kind" type="UnitKind" use="required"/>
        <xsd:attribute name="exponent" type="xsd:integer" use="default" value="1"/>
        <xsd:attribute name="scale" type="xsd:integer" use="default" value="1"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <!-- Rule -->
  <xsd:simpleType name="RuleType">
    <xsd:restriction base="xsd:string">
      <xsd:enumeration value="scalar"/>
      <xsd:enumeration value="rate"/>
    </xsd:restriction>
  </xsd:simpleType>
  <xsd:complexType name="Rule" abstract="true">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:attribute name="formula" type="xsd:string" use="required"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="AlgebraicRule">
    <xsd:complexContent>
      <xsd:extension base="Rule"/>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="AssignmentRule" abstract="true">
    <xsd:complexContent>
      <xsd:extension base="Rule">
        <xsd:attribute name="type" type="RuleType" use="default" value="scalar"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="CompartmentVolumeRule">
    <xsd:complexContent>
      <xsd:extension base="AssignmentRule">
        <xsd:attribute name="compartment" type="SName" use="required"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="SpecieConcentrationRule">
    <xsd:complexContent>
      <xsd:extension base="AssignmentRule">
        <xsd:attribute name="specie" type="SName" use="required"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="ParameterRule">
    <xsd:complexContent>
      <xsd:extension base="AssignmentRule">
        <xsd:attribute name="name" type="SName" use="required"/>
        <xsd:attribute name="units" type="SName" use="optional"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <!-- Reaction -->
  <xsd:element name="specieReference">
    <xsd:complexType>
      <xsd:complexContent>
        <xsd:extension base="SBase">
          <xsd:attribute name="specie" type="xsd:string" use="required"/>
          <xsd:attribute name="stoichiometry" type="xsd:integer" use="default" value="1"/>
          <xsd:attribute name="denominator" type="xsd:integer" use="default" value="1"/>
        </xsd:extension>
      </xsd:complexContent>
    </xsd:complexType>
  </xsd:element>
  <xsd:complexType name="Reaction">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:sequence>
          <xsd:element name="listOfReactants">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element ref="specieReference" maxOccurs="unbounded"/>
              </xsd:sequence>
            </xsd:complexType>
          </xsd:element>
          <xsd:element name="listOfProducts">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element ref="specieReference" maxOccurs="unbounded"/>
              </xsd:sequence>
            </xsd:complexType>
          </xsd:element>
          <xsd:element name="kineticLaw" type="KineticLaw" minOccurs="0"/>
        </xsd:sequence>
        <xsd:attribute name="name" type="SName" use="required"/>
        <xsd:attribute name="reversible" type="xsd:boolean" use="default" value="true"/>
        <xsd:attribute name="fast" type="xsd:boolean" use="default" value="false"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="KineticLaw">
    <xsd:complexContent>
      <xsd:extension base="SBase">
        <xsd:sequence>
          <xsd:element ref="listOfParameters" minOccurs="0"/>
        </xsd:sequence>
        <xsd:attribute name="formula" type="xsd:string" use="required"/>
        <xsd:attribute name="timeUnits" type="SName" use="optional"/>
        <xsd:attribute name="substanceUnits" type="SName" use="optional"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <!-- Top-level elements allowed in an SBML document. -->
  <xsd:complexType name="sbmlDocument">
    <xsd:sequence>
      <xsd:element name="model" type="Model"/>
    </xsd:sequence>
    <xsd:attribute name="xmlns"/>
    <xsd:attribute name="level" type="xsd:positiveInteger" use="required"/>
    <xsd:attribute name="version" type="xsd:positiveInteger" use="required"/>
  </xsd:complexType>
  <xsd:element name="sbml" type="sbmlDocument"/>
  <!-- The end. -->
</xsd:schema>