<!ELEMENT ebay (person*, category+, auction*)>
   <!-- am Anfang sind keine Personen und keine
        Auktionen eingetragen -->
<!ELEMENT person (name, address)>
  <!ATTLIST person id ID #REQUIRED
                   e-mail CDATA #REQUIRED>
 <!ELEMENT name (#PCDATA)>
 <!ELEMENT address EMPTY>
   <!ATTLIST address street CDATA #REQUIRED
                     zip CDATA #REQUIRED
                     city CDATA #REQUIRED>
<!ELEMENT category EMPTY>
  <!ATTLIST category name ID #REQUIRED
           has-subcategory IDREFS #IMPLIED
           subcategory-of IDREFS #IMPLIED>

<!ELEMENT auction (object, bid*)>
   <!-- bei einer neuen Auktion sind am Anfang keine
      bids eingetragen -->
  <!ATTLIST auction id ID #REQUIRED
                    seller IDREF #REQUIRED
                    start CDATA #REQUIRED
                    end CDATA #REQUIRED>
 <!ELEMENT object (type, year, description?, start-price)>
   <!ATTLIST object category IDREF #REQUIRED>
      <!-- oder IDREFS falls man mehrere erlauben will -->
  <!ELEMENT type (#PCDATA)>
  <!ELEMENT year (#PCDATA)>
  <!ELEMENT description (#PCDATA)>
  <!ELEMENT start-price (#PCDATA)>

 <!ELEMENT bid EMPTY>
   <!ATTLIST bid bidder IDREF #REQUIRED
                 date CDATA #REQUIRED
                 price CDATA #REQUIRED>