<!ELEMENT catalog (entry*)>
<!ATTLIST entry
xmlns:xlink CDATA
#FIXED "http://www.w3.org/1999/xlink">
<!ELEMENT entry (author?, title?, location)>
<!ELEMENT author (#PCDATA)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT location EMPTY>
<!ATTLIST entry
xlink:type (simple) #FIXED "simple"
xlink:href CDATA #REQUIRED
type CDATA #IMPLIED>
<!ATTLIST location
xlink:type (simple) #FIXED "simple"
xlink:href CDATA #REQUIRED>