45
Very Simple DTD
<!DOCTYPE company [
<!ELEMENT
company ((person|product)*)>
<!ELEMENT
person (ssn, name, office, phone?)>
<!ELEMENT
ssn
(#PCDATA)>
<!ELEMENT
name
(#PCDATA)>
<!ELEMENT
office (#PCDATA)>
<!ELEMENT
phone (#PCDATA)>
<!ELEMENT
product (pid, name, description?)>
<!ELEMENT
pid (#PCDATA)>
<!ELEMENT
description (#PCDATA)>
]>