topo.xsd

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning"
    >
    <xs:element name="interface">
        <xs:complexType>
            <xs:simpleContent>
                <xs:extension base="xs:string">
                    <xs:attribute type="xs:string" name="name" use="required"/>
                    <xs:attribute type="xs:string" name="external" use="optional"/>
                </xs:extension>
            </xs:simpleContent>
        </xs:complexType>
    </xs:element>
    <xs:element name="interfaces">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="interface" maxOccurs="unbounded" minOccurs="1"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:element name="switch">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="interfaces" minOccurs="1" maxOccurs="1"/>
            </xs:sequence>
            <xs:attribute type="xs:string" name="name" use="required"/>
        </xs:complexType>
        <xs:unique name="unique_interfaces">
            <xs:selector xpath="interfaces/interface"/>
            <xs:field xpath="@name"/>
        </xs:unique>
    </xs:element>
    <xs:element name="shared_interface">
        <xs:complexType>
            <xs:simpleContent>
                <xs:extension base="xs:string">
                    <xs:attribute type="xs:string" name="switch" use="required"/>
                    <xs:attribute type="xs:string" name="interface" use="required"/>
                </xs:extension>
            </xs:simpleContent>
        </xs:complexType>
    </xs:element>
    <xs:element name="sides">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="shared_interface" maxOccurs="2" minOccurs="2"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:element name="link">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="sides"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:element name="switches">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="switch" maxOccurs="unbounded" minOccurs="0"/>
            </xs:sequence>
        </xs:complexType>
        <xs:unique name="unique_switchname">
            <xs:selector xpath="switch"/>
            <xs:field xpath="@name"/>
        </xs:unique>
    </xs:element>
    <xs:element name="links">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="link" maxOccurs="unbounded" minOccurs="0"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:element name="network" vc:minVersion="1.1">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="switches"/>
                <xs:element ref="links"/>
            </xs:sequence>
            <!-- Why must you hurt me XML -->
            <xs:assert id="a" test="every $si in //shared_interface satisfies //switches/switch[@name=$si/@switch]/interfaces/interface[@name=$si/@interface]"/>
        </xs:complexType>
    </xs:element>
</xs:schema>