<!ELEMENT Course_Catalog (Department*)>
   <!ATTLIST Department Code ID #REQUIRED>
   <!ELEMENT Department (Title,Chairs,Curse*)>
   <!ELEMENT Title (#PCDATA)>
   <!ELEMENT Chairs (Professor*)>
   <!ELEMENT Curse (Title, Description?, Instructors, Prerequisites?) >
   <!ATTLIST Curse Number ID #REQUIRED
                   Enrollment CDATA #IMPLIED>
   <!ELEMENT Professor (First_Name, Middle_Initial?, Last_Name) >
   <!ELEMENT First_Name (#PCDATA) >
   <!ELEMENT Middle_Initial (#PCDATA) >
   <!ELEMENT Last_Name (#PCDATA) >
   <!ELEMENT Description (#PCDATA)>
   <!ELEMENT Instructors (Lecturer?,Professor+)>
   <!ELEMENT Lecturer (First_Name,Middle_Initial? ,Last_Name) >
   <!ELEMENT Prerequisites (Prereq*) >