> SQL and relational database management systems or RDBMS were invented simultaneously by Edgar F. Codd in the early 1970s. Codd didn't invent SQL. Donald Cham

> SQL and relational database management systems or RDBMS were invented simultaneously by Edgar F. Codd in the early 1970s. Codd didn't invent SQL. Donald Chamberlin and Raymond Boyce did. > SQL is originally based on relational algebra and tuple relational calculus Maybe "originally based on", but not "an implementation of". For example, it is perfectly possible for an SQL query to return duplicate rows, which isn't possible under relational algebra/calculus, a relation being by definition a set of rows (or, more precisely, of tuples).