<xsd:element name="oval_system_characteristics">
    <xsd:annotation>
        <xsd:documentation>The system_characteristics element is the root of an OVAL System Characteristics Document, and must occur exactly once. Its purpose is to bind together the four major sections of a system characteristics file - generator, system_info, collected_objects, and system_data - which are the children of the oval_system_characteristics element.</xsd:documentation>
    </xsd:annotation>
    <xsd:complexType>
        <xsd:sequence>
            <xsd:element name="generator" type="oval:GeneratorType" minOccurs="1" maxOccurs="1">
                <xsd:annotation>
                    <xsd:documentation>The generator section must be present and provides information about when the system characteristics file was compiled and under what version.</xsd:documentation>
                </xsd:annotation>
            </xsd:element>
            <xsd:element name="system_info" type="oval-sc:SystemInfoType" minOccurs="1" maxOccurs="1">
                <xsd:annotation>
                    <xsd:documentation>The required system_info element is used to record information about the system being described.</xsd:documentation>
                </xsd:annotation>
            </xsd:element>
            <xsd:element name="collected_objects" type="oval-sc:CollectedObjectsType" minOccurs="0" maxOccurs="1">
                <xsd:annotation>
                    <xsd:documentation>The optional collected_objects section is used to associated the ids of the OVAL Objects collected with the system characteristics items that have been defined. The collected_objects section provides a listing of all the objects used to generate this system characteristics file.</xsd:documentation>
                </xsd:annotation>
            </xsd:element>
            <xsd:element name="system_data" type="oval-sc:SystemDataType" minOccurs="0" maxOccurs="1">
                <xsd:annotation>
                    <xsd:documentation>The optional system_data section defines the specific characteristics that have been collected from the system.</xsd:documentation>
                </xsd:annotation>
            </xsd:element>
            <xsd:element ref="ds:Signature" minOccurs="0" maxOccurs="1">
                <xsd:annotation>
                    <xsd:documentation>The optional Signature element allows an XML Signature as defined by the W3C to be attached to the document. This allows authentication and data integrity to be provided to the user. Enveloped signatures are supported. More information about the official W3C Recommendation regarding XML digital signatures can be found at http://www.w3.org/TR/xmldsig-core/.</xsd:documentation>
                </xsd:annotation>
            </xsd:element>
        </xsd:sequence>
    </xsd:complexType>
    <xsd:key name="objectKey">
        <xsd:annotation>
            <xsd:documentation>Enforce uniqueness amongst the individual object ids used in the collected object section.</xsd:documentation>
        </xsd:annotation>
        <xsd:selector xpath="oval-sc:collected_objects/oval-sc:object" />
        <xsd:field xpath="@id" />
        <xsd:field xpath="@version" />
        <xsd:field xpath="@variable_instance" />
    </xsd:key>
    <xsd:key name="itemKey">
        <xsd:annotation>
            <xsd:documentation>Enforce uniqueness amongst the individual item ids.</xsd:documentation>
        </xsd:annotation>
        <xsd:selector xpath="oval-sc:system_data/*" />
        <xsd:field xpath="@id" />
    </xsd:key>
    <xsd:keyref name="itemKeyRef" refer="oval-sc:itemKey">
        <xsd:annotation>
            <xsd:documentation>Require that each item reference refers to a valid item id.</xsd:documentation>
        </xsd:annotation>
        <xsd:selector xpath="oval-sc:collected_objects/oval-sc:object/oval-sc:reference" />
        <xsd:field xpath="@item_ref" />
    </xsd:keyref>
</xsd:element>