Finished DTD
<!ELEMENT category (#PCDATA)>
<!ELEMENT abstract (#PCDATA)>
<!ELEMENT keyword (#PCDATA)>
<!ELEMENT last_updated (#PCDATA)>
<!ELEMENT copyright (#PCDATA)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT instruments (#PCDATA)>
<!ELEMENT publisher (#PCDATA)>
<!ELEMENT length (#PCDATA)>
<!ELEMENT date (year | ISODate)>
<!ELEMENT year (#PCDATA)>
<!ELEMENT ISODate (#PCDATA)>
<!ELEMENT catalog (category, cataloging_info, last_updated,
copyright, maintainer, (composer | composition)*)>
<!ELEMENT cataloging_info (abstract, keyword+)>
<!ELEMENT description (#PCDATA | ul | a | cite | p)*>
<!ELEMENT cite (#PCDATA | a)*>
<!ELEMENT ul (li*)>
<!ELEMENT li (#PCDATA)>
<!ELEMENT a (#PCDATA)>
<!ELEMENT p (#PCDATA)>
<!ELEMENT maintainer (name)>
<!ELEMENT name (first_name, middle_name, last_name)>
<!ELEMENT first_name (#PCDATA)>
<!ELEMENT middle_name (#PCDATA)>
<!ELEMENT last_name (#PCDATA)>
<!ATTLIST maintainer email CDATA #REQUIRED
url CDATA #IMPLIED>
<!ELEMENT composer (name)>
<!ATTLIST composer id ID #REQUIRED>
<!ELEMENT composition (title, date, length?,
instruments, description?, publisher?)>
<!ATTLIST composition composer IDREFS #REQUIRED>
<!ATTLIST a href CDATA #REQUIRED>