Consider as shown below, and suppose that authors could also appear as top level elements. What change would have to be done to the relational schema?

<!DOCTYPE bibliography [

<!ELEMENT book (title, author+, year, publisher, place?)>

<!ELEMENT article (title, author+, journal, year, number, volume, pages?)>

<!ELEMENT author ( last-name, first-name) >

<!ELEMENT title ( #PCDATA )>

· · · similar PCDATA declarations for year, publisher, place, journal, year,

number, volume, pages, last-name and first-name

] >