thelw toy teleytaioy vivlioy ton titlo
//book[last()]/title


thelw oles tis kathgories twn vivliwn
//book/@category

thelw na mou emfanisei olous tous authors poy to book tous exei timh megalyterh tou 10
//book[price>10]
/author

thelw na mou emfanisei to price tou book me title the The Einstein Theory of Relativity
//book[title="The Einstein Theory of Relativity"]/price

thelw na mou emfanisei tou prwtou book to price
//book[1]/price

thelw na mou emfanisei to 1o author tou book p exei history category 
//book[@category="history"]/author[1]

thelw ola ta nodes twn book
//book/node() 

thelw na dw times kai tilous mazi
//book/title | //book/price

thelw olous tou tilous twn book pou h timh tous den einai 3.99
//book[price!=3.99]/title