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.
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.
all relational database dbms products are built on this model -e.f. codd applied the concepts of a branch of math called relational algebra to the problem of databases