diff --git a/Schemas/markup.xsd b/Schemas/markup.xsd
index 5918505..26d53f6 100644
--- a/Schemas/markup.xsd
+++ b/Schemas/markup.xsd
@@ -128,8 +128,8 @@
         <xs:attributeGroup ref="FileAttributes"/>
     </xs:complexType>
     <xs:attributeGroup name="FileAttributes">
-        <xs:attribute name="IfcProject" type="IfcGuid" use="optional"/>
-        <xs:attribute name="IfcSpatialStructureElement" type="IfcGuid" use="optional"/>
+        <xs:attribute name="IfcProject" type="IfcGuid"/>
+        <xs:attribute name="IfcSpatialStructureElement" type="IfcGuid"/>
         <xs:attribute name="IsExternal" type="xs:boolean" default="true"/>
     </xs:attributeGroup>
     <!-- Reference to a document inside of the topic folder or a url pointing to the web -->
@@ -165,10 +165,4 @@
         </xs:sequence>
         <xs:attribute name="Guid" type="Guid" use="required"/>
     </xs:complexType>
-    <xs:simpleType name="IfcGuid">
-        <xs:restriction base="xs:string">
-            <xs:length value="22"/>
-            <xs:pattern value="[0-9A-Za-z_$]*"/>
-        </xs:restriction>
-    </xs:simpleType>
 </xs:schema>
diff --git a/Schemas/shared-types.xsd b/Schemas/shared-types.xsd
index 93dd484..842ceba 100644
--- a/Schemas/shared-types.xsd
+++ b/Schemas/shared-types.xsd
@@ -11,4 +11,10 @@
             <xs:whiteSpace value="collapse"/>
         </xs:restriction>
     </xs:simpleType>
+    <xs:simpleType name="IfcGuid">
+        <xs:restriction base="xs:normalizedString">
+            <xs:length value="22"/>
+            <xs:pattern value="[0-9A-Za-z_$]*"/>
+        </xs:restriction>
+    </xs:simpleType>
 </xs:schema>
diff --git a/Schemas/visinfo.xsd b/Schemas/visinfo.xsd
index 6e3053a..3df0a88 100644
--- a/Schemas/visinfo.xsd
+++ b/Schemas/visinfo.xsd
@@ -163,7 +163,7 @@
             <xs:element name="OriginatingSystem" type="NonEmptyOrBlankString" minOccurs="0"/>
             <xs:element name="AuthoringToolId" type="NonEmptyOrBlankString" minOccurs="0"/>
         </xs:sequence>
-        <xs:attribute ref="IfcGuid"/>
+        <xs:attribute name="IfcGuid" type="IfcGuid"/>
     </xs:complexType>
     <xs:attribute name="Color">
         <xs:simpleType>
@@ -173,14 +173,6 @@
             </xs:restriction>
         </xs:simpleType>
     </xs:attribute>
-    <xs:attribute name="IfcGuid">
-        <xs:simpleType>
-            <xs:restriction base="xs:normalizedString">
-                <xs:length value="22"/>
-                <xs:pattern value="[0-9A-Za-z_$]*"/>
-            </xs:restriction>
-        </xs:simpleType>
-    </xs:attribute>
     <xs:complexType name="Line">
         <xs:sequence>
             <xs:element name="StartPoint" type="Point"/>