(Q1) In the second chapter of the document named "zoo.xml", find the
         figure(s) with caption "Tree Frogs". 

              doc("zoo.xml")//chapter[2]//figure[caption = "Tree Frogs"]

(Q2) Find captions of figures that are referenced by <figref> elements in the
         chapter of "zoo.xml" with title "Frogs". 

              doc("zoo.xml")//chapter[title = "Frogs"]
                 //figref/@refid=>fig/caption

(Q3) List the names of the second-level managers of all employees whose
	  rating is "Poor".  

              //emp[rating = "Poor"]/@mgr=>emp/@mgr=>emp/name

(Q4) List the titles of books published by Morgan Kaufmann in 1998. 

              FOR $b IN doc("bib.xml")//book
              WHERE $b/publisher = "Morgan Kaufmann"
              AND $b/year = "1998"
              RETURN {$b/title}

(Q5) List each publisher and the average price of its books. 

              FOR $p IN distinct(doc("bib.xml")//publisher)
              LET $a := avg(doc("bib.xml")//book[publisher = $p]/price)
              RETURN 
                 <publisher>
                    <name> {$p/text()} </name> 
                    <avgprice> {$a} </avgprice>
                 </publisher>

(Q6) List the publishers who have published more than 100 books. 

              <big_publishers>
                 {
                  FOR $p IN distinct(doc("bib.xml")//publisher)
                  LET $b := doc("bib.xml")//book[publisher = $p]
                  WHERE count($b) > 100
                  RETURN {$p}
                 }
              </big_publishers>

(Q7) Invert the structure of the input document so that, instead of each book
         element containing a sequence of authors, each distinct author
         element contains a sequence of book-titles. 

              <author_list>
                 {
                  FOR $a IN distinct(doc("bib.xml")//author)
                  RETURN
                    <author>
                       <name> {$a/text()} </name>
                       {
                        FOR $b IN doc("bib.xml")//book[author = $a]
                        RETURN $b/title
                       }
                    </author>
                 }
              </author_list>

(Q8)List all books with price greater than $100, in order by first author;
         within each group of books with the same first author, list the
         books in order by title.  

              FOR $b IN doc("bib.xml")//book[price > 100] 
	      ORDER BY $b/author[1], $b/title
	      RETURN {$b}

(Q9) Find titles of books in which sailing is mentioned in every paragraph. 

              FOR $b IN //book
              WHERE EVERY $p IN $b//para SATISFIES
                 contains($p, "sailing")
              RETURN {$b/title}


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Interval inclusion model for node numbering is important for cheap
determination of ancestor-descendant relationships.