<appendix> requires @xml:id attribute.

Doc/Sd1/appendix.xml

 <?xml version="1.0" encoding="UTF-8"?>
-<appendix annotations="slide" version="5.1"
+<appendix annotations="slide" version="5.1" xml:id="sd1_appendix"
           xmlns="http://docbook.org/ns/docbook"
           xmlns:xlink="http://www.w3.org/1999/xlink"
           xmlns:xila="http://www.w3.org/2001/XInclude/local-attributes"

Doc/lectures.xml

@@ -97,7 +97,7 @@
     <xi:include href="Sd1/appendix.xml" xpointer="element(/1)"/>
   </part>
 
-  <part xml:id="sda1" annotations="forumId=6;">
+  <part annotations="forumId=6;" xml:id="sda1">
     <title>Structured Data and Applications 1</title>
 
     <xi:include href="Sda1/prerequisites.xml" xpointer="element(/1)"/>
@@ -114,7 +114,7 @@
 
     <xi:include href="Sda1/mongodb.xml" xpointer="element(/1)"/>
 
-    <appendix>
+    <appendix xml:id="sda1_appendix">
       <title>Appendix</title>
 
       <xi:include href="Sda1/projects.xml" xpointer="element(/1)"/>

ws/Xmlmind/Patch/040_hdmBusinessIntegrityRules.patch

@@ -26,7 +26,7 @@
 +   </s:pattern>
 +
 +   <s:pattern name="Mandatory Id definition constraint">
-+      <s:rule context="db:preface|db:chapter|db:section|db:figure|db:equation|db:table|db:qandaset">
++      <s:rule context="db:preface|db:chapter|db:section|db:appendix|db:figure|db:equation|db:table|db:qandaset">
 +         <s:assert test="@xml:id">Each chapter,section, subection,... must have a unique id.</s:assert>
 +      </s:rule>
 +   </s:pattern>
@@ -76,7 +76,7 @@
 +
 +   <s:pattern>
 +      <s:title>Mandatory Id definition constraint</s:title>
-+      <s:rule context="db:preface|db:chapter|db:section|db:figure|db:equation|db:table|db:qandaset">
++      <s:rule context="db:preface|db:chapter|db:section|db:appendix|db:figure|db:equation|db:table|db:qandaset">
 +         <s:assert test="@xml:id">Each chapter,section, subection,... must have a unique id.</s:assert>
 +      </s:rule>
 +   </s:pattern>