Ex 7.2 DTD document for car catalog

<?xml version = "1.0" encoding = "utf-8"?>
<!ELEMENT cars(ad+)>
<!ELEMENT ad(make,model,year,color,engine,number_of_doors,transmission_type,accessories)>
<!ELEMENT make(# PCDATA)>
<!ELEMENT model(#PCDATA)>
<!ELEMENT year(#PCDATA)>
<!ELEMENT color(#PCDATA)>
<!ELEMENT engine(number_of_cylinders,fuel_system)>
<!ELEMENT number_of_doors(#PCDATA)>
<!ELEMENT transmission_type(#PCDATA)>
<!ELEMENT accessories(#PCDATA)>

<!ATTLIST accessories radio CDATA #IMPLIED>
<!ATTLIST accessories air_conditioner CDATA #IMPLIED>
<!ATTLIST accessories power_window CDATA #REQUIRED>
<!ATTLIST accessories power_steering CDATA #REQUIRED>
<!ATTLIST accessories power_brake CDATA #REQUIRED>