@xml:id for qandaset according to newly defined schematron rule

Doc/course.xml

@@ -4563,7 +4563,8 @@ PUBLIC "-//OASIS//DTD DocBook V3.1//EN"          docbook.dtd
           both are accessible.</para>
           <qandaset defaultlabel="qanda" xml:id="example_public_system">
-            <title>Relation between public and system identifiers</title>
+            <title>Relation between PUBLIC and SYSTEM identifiers and their
+            relation to catalogs.</title>
             <qandadiv>
               <qandaentry>
@@ -4622,8 +4623,6 @@ double quote character.</errortext></programlisting>
               <qandaentry xml:id="example_public_dtdlookup">
                 <question>
-                  <label>DTD lookup by PUBLIC identifier</label>
-
                   <para>Modify the document of the preceding exercise
                   by:</para>
@@ -4658,9 +4657,9 @@ double quote character.</errortext></programlisting>
                   <code>PUBLIC</code> identifier.</para>
                   <para>This assumption is indeed true: In the indicated
-                  options menu we find that a master catalog file
+                  options menu we retrieve a master catalog file
                   <filename>/usr/share/.../frameworks/catalog.xml</filename>
-                  is used for looking up <code>PUBLIC</code>
+                  being used for looking up <code>PUBLIC</code>
                   identifiers:</para>
                   <programlisting>&lt;?xml version="1.0"?&gt;
@@ -7874,7 +7873,7 @@ public class Driver {
           <section xml:id="sda1SaxView">
             <title>A limited view on a given XML document instance</title>
-            <qandaset defaultlabel="qanda">
+            <qandaset defaultlabel="qanda" xml:id="sda1QandamemoView">
               <title>A specific view on memo documents</title>
               <qandadiv>