schema.xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!-- HackThisSite.org
     programming challenge 4 -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           elementFormDefault="qualified">
    <xs:complexType name="LineType">
        <xs:all>
            <xs:element ref="XStart"/>
            <xs:element ref="XEnd"/>
            <xs:element ref="YStart"/>
            <xs:element ref="YEnd"/>
            <xs:element ref="Color" minOccurs="0"/>
        </xs:all>
    </xs:complexType>
    <xs:complexType name="ArcType">
        <xs:all>
            <xs:element ref="XCenter"/>
            <xs:element ref="YCenter"/>
            <xs:element ref="Radius"/>
            <xs:element ref="ArcStart"/>
            <xs:element ref="ArcExtend"/>
            <xs:element ref="Color" minOccurs="0"/>
        </xs:all>
    </xs:complexType>
    <xs:element name="XStart" type="xs:double"/>
    <xs:element name="XEnd" type="xs:double"/>
    <xs:element name="YStart" type="xs:double"/>
    <xs:element name="YEnd" type="xs:double"/>
    <xs:element name="XCenter" type="xs:double"/>
    <xs:element name="YCenter" type="xs:double"/>
    <xs:element name="Radius" type="xs:double"/>
    <xs:element name="ArcStart" type="xs:double"/>
    <xs:element name="ArcExtend" type="xs:double"/>
    <xs:element name="Color">
        <xs:simpleType>
            <xs:restriction base="xs:string">
                <xs:enumeration value="blue"/>
                <xs:enumeration value="green"/>
                <xs:enumeration value="red"/>
                <xs:enumeration value="yellow"/>
            </xs:restriction>
        </xs:simpleType>
    </xs:element>
    <xs:element name="ppcPlot">
        <xs:complexType>
            <xs:choice minOccurs="0" maxOccurs="unbounded">
                <xs:element name="Line" type="LineType"
                            minOccurs="0" maxOccurs="unbounded"/>
                <xs:element name="Arc" type="ArcType"
                            minOccurs="0" maxOccurs="unbounded"/>
            </xs:choice>
        </xs:complexType>
    </xs:element>
</xs:schema>