--- a/schema/ssm.xsd	Wed Oct 02 16:56:11 2019 +0200
+++ b/schema/ssm.xsd	Wed Oct 02 19:10:46 2019 +0200
@@ -58,8 +58,44 @@
 			<xs:element name="id" type="ID"/>
 			<xs:element name="text" type="xs:string" minOccurs="1" maxOccurs="unbounded"/>
 			<xs:element name="note" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
+			<xs:element name="link" type="Link" minOccurs="0" maxOccurs="unbounded"/>
 			<xs:element name="item" type="Item" minOccurs="0" maxOccurs="unbounded"/>
 		</xs:sequence>
 	</xs:complexType>
+	
+	<xs:complexType name="Link">
+		<xs:sequence>
+			<xs:element name="url" type="URL"/>
+			<xs:element name="type" type="LinkType"/>
+			<xs:element name="title" type="xs:string"/>
+			<xs:element name="description" type="xs:string" minOccurs="0"/>
+			<xs:element name="quotation" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
+		</xs:sequence>
+	</xs:complexType>
+	
+	<xs:simpleType name="LinkType" final="restriction" >
+		<xs:restriction base="xs:string">
+			<xs:enumeration value="related">
+				<xs:annotation>
+					<xs:documentation>
+						generic link
+					</xs:documentation>
+				</xs:annotation>
+			</xs:enumeration>
+			<xs:enumeration value="compatible">
+				<xs:annotation>
+					<xs:documentation>
+						link to a particular compatible rule in another guidelines
+					</xs:documentation>
+				</xs:annotation>
+			</xs:enumeration>
+		</xs:restriction>
+	</xs:simpleType>
+	
+	<xs:simpleType name="URL">
+		<xs:restriction base="xs:string">
+			<xs:pattern value="https?://[^ ]+"/>
+		</xs:restriction>
+	</xs:simpleType>
 
 </xs:schema>