Formal Definition A basic expression in the relational algebra consists of either one of the following: A relation in the database A constant relation Let E,and E2 be relational-algebra expressions;the following are all relational-algebra expressions: E10 E2 E1-E2 E1x E2 Op(E),P is a predicate on attributes in E Is(E),S is a list consisting of some of the attributes in E Px(E),x is the new name for the result of E Database System Concepts-6th Edition 6.11 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 6 6.11 ©Silberschatz, Korth and Sudarshan th Edition Formal Definition A basic expression in the relational algebra consists of either one of the following: A relation in the database A constant relation Let E1 and E2 be relational-algebra expressions; the following are all relational-algebra expressions: E1  E2 E1 – E2 E1 x E2 p (E1 ), P is a predicate on attributes in E1 s (E1 ), S is a list consisting of some of the attributes in E1  x (E1 ), x is the new name for the result of E1