--- /dev/null
+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" targetNamespace="http://www.w3.org/XML/1998/namespace" xmlns:sig="http://www.w3.org/2000/09/xmldsig#">
+ <xs:import schemaLocation="credential.xsd"/>
+ <xs:import namespace="http://www.w3.org/2000/09/xmldsig#" schemaLocation="sig.xsd"/>
+ <xs:attribute name="id" type="xs:ID">
+ <xs:annotation>
+ <xs:documentation>The ID for signature referencing.</xs:documentation>
+ </xs:annotation>
+ </xs:attribute>
+</xs:schema>