xml_xquery.txt

             					(: Answer for 2.1 :)

let $xml := doc("/db/books.xml")


let $main_author := "Jeff Ullman"  (: Given Name of the author :)

for $bt in $xml/biblio/author[name = $main_author]/book/title/string() (: all books of given author :)
 
for $other in $xml/biblio/author[name != $main_author]

let $co_authors := string-join(($other/book[title = $bt]/../name/string(),$bt),":")

for $a in $co_authors
let $result := $a where count(tokenize($a,":")) eq 2

return $result



						(: Answer for 2.2 :)

let $xml := doc("/db/books.xml")

(: Price list of all books where each book is considered only once :)

let $prices := for $uniq_book_with_price in distinct-values($xml/biblio/author/book)
               return xs:integer(tokenize($uniq_book_with_price,' ')[position() eq last()])

(: Name of the authors whose books average is at least 
   twice the average book price over all books :)

return distinct-values(
    for $a in $xml/biblio/author
    where avg($a//price) >= 2*avg($prices)
    return $a/name/string()   (: For the auhtor tag with children element use only "$a" :)
)



					      (: Answer for 2.3 :)

let $xml := doc("/db/books.xml")
                                    
(: Assumption: Book titles are unique. A book has same title and year throughout the xml file :)


<biblio>
{ 
     let $book_titles := distinct-values($xml/biblio//title)
  
     for $bt in $book_titles
     
     let $p := $xml/biblio/author/book[title=$bt]
     
     return  <book year='{distinct-values($p/@year/string())}'>
     
                <title> {$bt} </title> 
                
                <price> {distinct-values($p/price)} </price> 
                
                <authors>
                   { 
                     for $author in $xml/biblio/author/book[title=$bt]/../name
                     return <author> 
                     			{$author/string()} 
                     	   </author> 
                   }
                </authors>
       
            </book>
}
</biblio>



				(: New DTD where authors are listed under their books :)
						(: DTD data format B :)

<!DOCTYPE biblio[
<!ELEMENT biblio (book*)>
<!ELEMENT book (title, price, authors)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT price (#PCDATA)>
<!ATTLIST book year CDATA #REQUIRED>
<!ELEMENT authors (author+)>
<!ELEMENT author (name)>
<!ELEMENT name (#PCDATA)>
]>