Nesting and Unnesting

1. The transformation of a nested relation into 1NF is called unnesting.
2. Example. To complete unnest the doc relation, we have

    
   		 select name, A as author, date.day, date.month, date.year, 
   	K as keyword
   
   		 from doc as B, B.author-list as A, B.keyword-list 
   as K
   
   

3. The reverse operation of transformation of a 1NF relation into a nested relation is called nesting.
4. Example. To nest the relation flat-doc on the attribute keyword, we have

    
   		 select title, author, (day, month, year) as date, 
   	set(keyword) as keyword-list
   
   		 from flat-doc
   
   		 groupby title, author, date
   
   

   This wil generate the following table.

   

5. Example. To convert flat-doc back to the nested table doc, we have

    
   		 select title, set(author) as author-list, 
   	(day, month, year) as date, 
   	set(keyword) as keyword-list
   
   		 from flat-doc
   
   		 groupby title, date