<!ELEMENT  amazon (books, software)>
<!ELEMENT  books (book)*>
<!ELEMENT software (program)*>
<!ELEMENT  book (title,author+,rating?,price)>
<!ELEMENT  program (title,version?,rating?,price,platform+)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT author (#PCDATA)>
<!ELEMENT rating (#PCDATA)>
<!ELEMENT price (#PCDATA)>
<!ELEMENT version (#PCDATA)>
<!ELEMENT platform (#PCDATA)>

<!ATTLIST book category CDATA #REQUIRED>
<!ATTLIST program category CDATA #REQUIRED>
