Paolo Atzeni Peter P. Chen Completeness of Query Languages for the Entity-Relationship Model. 109-122 1981 ER db/conf/er/er81.html#AtzeniC81 conf/er/81 db/conf/er/AtzeniC81.html er81/ER81-P109.pdf conf/er/AtzeniBLV81 ... journals/tods/Chen76 persons/Codd72 books/aw/Date77 ... ... ... books/cs/Ullman80