Introduction to Databases with Stanford University : DTD Exercises

The XML data is at http://s3.amazonaws.com/dbclass-resources/docs/courses-noID.xml

<!ELEMENT Course_Catalog (Department*)>
<!ELEMENT Department (Title, Chair, Course+)> 
<!ATTLIST Department Code CDATA #REQUIRED> 

<!ELEMENT Chair (Professor)> 
<!ELEMENT Course (Title, Description*, Instructors, Prerequisites*)> 
  <!ATTLIST Course Number CDATA #REQUIRED Enrollment CDATA #IMPLIED> 

<!ELEMENT Instructors (Lecturer|Professor)+> 
<!ELEMENT Prerequisites (Prereq*)> 
<!ELEMENT Lecturer (First_Name,Middle_Initial*,Last_Name)+> 
<!ELEMENT Professor (First_Name,Middle_Initial*,Last_Name)+> 
<!ELEMENT Title (#PCDATA)> 
<!ELEMENT Description (#PCDATA)> 
<!ELEMENT First_Name (#PCDATA)> 
<!ELEMENT Last_Name (#PCDATA)> 
<!ELEMENT Middle_Initial (#PCDATA)> 
<!ELEMENT Prereq (#PCDATA)>