<!ENTITY % added "added CDATA #REQUIRED" >
<!ENTITY % employee_content "address, department?" >
<!ENTITY % employee_attributes "id CDATA #REQUIRED %added;" >
<!ELEMENT company (people) >
<!ELEMENT people (customer | employee | temporary_employee)* >
<!ELEMENT address (#PCDATA) >
<!ELEMENT customer (name, address) >
<!ATTLIST customer %added; >
<!ELEMENT name (#PCDATA)>
<!ELEMENT employee (%employee_content;) >
<!ATTLIST employee %employee_attributes; >
<!ELEMENT temporary_employee (%employee_content;) >
<!ATTLIST temporary_employee %employee_attributes; >