theoretical way of manipulating table contents using relational operators (select, project, join, union, intersection, subtract, product, rename)
defines the theoretical way of manipulating table contents using relational operators, act on existing tables to produce new tables. ex select, project, join, union, subtract
domain — the set of relations operations:  - unary: select, project - join: cartesian product, theta-join, natural join - set operations: union, intersection, difference - others: division