A More Complex DTD

<!ELEMENT SONG (TITLE, PHOTO?, COMPOSER+, PRODUCER*, 
 PUBLISHER*, LENGTH?, YEAR?, ARTIST+)>
<!ATTLIST SONG xmlns       CDATA #REQUIRED
               xmlns:xlink CDATA #REQUIRED>
<!ELEMENT TITLE (#PCDATA)>

<!ELEMENT PHOTO EMPTY>
<!ATTLIST PHOTO xlink:type CDATA #FIXED "simple"
                xlink:href CDATA #REQUIRED
                xlink:show CDATA #IMPLIED
                ALT        CDATA #REQUIRED
                WIDTH      CDATA #REQUIRED
                HEIGHT     CDATA #REQUIRED
>

<!ELEMENT COMPOSER (#PCDATA)>
<!ELEMENT PRODUCER (#PCDATA)>
<!ELEMENT PUBLISHER (#PCDATA)>
<!ATTLIST PUBLISHER xlink:type CDATA #IMPLIED
                    xlink:href CDATA #IMPLIED
>

<!ELEMENT LENGTH (#PCDATA)>
<!-- This should be a four digit year like "1999",
     not a two-digit year like "99" -->
<!ELEMENT YEAR (#PCDATA)>

<!ELEMENT ARTIST (#PCDATA)>