<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:gml="http://www.opengis.net/gml" xmlns:ogc="http://www.opengis.net/ogc" elementFormDefault="qualified" targetNamespace="http://www.opengis.net/ogc" version="1.1">
  <xsd:element name="Add" substitutionGroup="ogc:expression" type="ogc:BinaryOperatorType"/>
  <xsd:element name="Sub" substitutionGroup="ogc:expression" type="ogc:BinaryOperatorType"/>
  <xsd:element name="Mul" substitutionGroup="ogc:expression" type="ogc:BinaryOperatorType"/>
  <xsd:element name="Div" substitutionGroup="ogc:expression" type="ogc:BinaryOperatorType"/>
  <xsd:element name="PropertyName" substitutionGroup="ogc:expression" type="ogc:PropertyNameType"/>
  <xsd:element name="Function" substitutionGroup="ogc:expression" type="ogc:FunctionType"/>
  <xsd:element name="Literal" substitutionGroup="ogc:expression" type="ogc:LiteralType"/>
  <xsd:element abstract="true" name="expression" type="ogc:ExpressionType"/>
  <xsd:complexType name="ExpressionType" abstract="true"/>
  <xsd:complexType name="BinaryOperatorType">
    <xsd:complexContent mixed="false">
      <xsd:extension base="ogc:ExpressionType">
        <xsd:sequence>
          <xsd:element minOccurs="2" maxOccurs="2" ref="ogc:expression"/>
        </xsd:sequence>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="FunctionType">
    <xsd:complexContent mixed="false">
      <xsd:extension base="ogc:ExpressionType">
        <xsd:sequence>
          <xsd:element minOccurs="0" maxOccurs="unbounded" ref="ogc:expression"/>
        </xsd:sequence>
        <xsd:attribute name="name" type="xsd:string" use="required"/>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="LiteralType">
    <xsd:complexContent mixed="true">
      <xsd:extension base="ogc:ExpressionType">
        <xsd:sequence>
          <xsd:any minOccurs="0"/>
        </xsd:sequence>
      </xsd:extension>
    </xsd:complexContent>
  </xsd:complexType>
  <xsd:complexType name="PropertyNameType">
    <xsd:complexContent mixed="true">
      <xsd:extension base="ogc:ExpressionType"/>
    </xsd:complexContent>
  </xsd:complexType>
</xsd:schema>