<!ELEMENT book (title, author, character*)>
<!ATTLIST book
	isbn CDATA #REQUIRED
>
<!ELEMENT title (#PCDATA)>
<!ELEMENT author (#PCDATA)>
<!ELEMENT character (name, friend-of*, since, qualification)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT friend-of (#PCDATA)>
<!ELEMENT since (#PCDATA)>
<!ELEMENT qualification (#PCDATA)>