<!ELEMENT bookstore (book)*> 
<!ELEMENT book (title,author*,price)>
<!ATTLIST book genre CDATA #REQUIRED>
<!ELEMENT title (#PCDATA)>
<!ELEMENT author (name | (first-name,last-name))>
<!ELEMENT price (#PCDATA)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT first-name (#PCDATA)>
<!ELEMENT last-name (#PCDATA)>