Add XML schema

bpmn-icon.xsd

@@ -0,0 +1,24 @@
+<xs:schema id="bpmn-icon" version="0.1" 
+    targetNamespace="http://www.omg.org/spec/BPMN/non-normative/Icon"
+    xmlns:icon="http://www.omg.org/spec/BPMN/non-normative/Icon"
+    xmlns:xs="http://www.w3.org/2001/XMLSchema"
+    elementFormDefault="qualified">
+
+    <xs:element name="iconDefinition" type="icon:tIconDefinition"/>
+
+    <xs:complexType name="tIconDefinition">
+        <xs:attribute name="id" type="xs:ID" use="required"/>
+        <xs:attribute name="href" type="xs:anyURI" use="required"/>
+    </xs:complexType>
+
+    <xs:attributeGroup name="iconRefAttributeGroup">
+        <xs:attribute name="iconRef" type="xs:QName" use="optional">
+            <xs:annotation>
+                <xs:documentation>
+                    This attribute points to the id of the iconDefinition.
+                </xs:documentation>
+            </xs:annotation>
+        </xs:attribute>
+    </xs:attributeGroup>
+
+</xs:schema>

example.bpmn

@@ -3,7 +3,12 @@
   xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI"
   xmlns:dc="http://www.omg.org/spec/DD/20100524/DC"
   xmlns:icon="http://www.omg.org/spec/BPMN/non-normative/Icon"
-  id="Definitions" targetNamespace="http://example.org">
+  id="Definitions" targetNamespace="http://example.org"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="
+    http://www.omg.org/spec/BPMN/non-normative/Icon
+    ./bpmn-icon.xsd
+  ">
   <process id="ProcessWithIcon">
     <startEvent id="StartEvent" />
   </process>