the relational model of data is based on the concept of a relation  proposed in 1970 by e.f. codd (ibm), first commercial system in 1981-82.
introduced in 1970, e.f codd created, an ibm manager based on &"relational algebra,&" which is now the standard model for commercial (relational) dbms products.
ted codd introduced this model  using relational calculus and relational algebra