Access path selection in a relational database management system

In a high level query and data manipulation language such as SQL, requests are stated non-procedurally, without reference to access paths. This paper describes hou System R chooses access paths for both simple (single relation) and complex queries (such as joins), given a user specification of desired data as a boolean expression of predicates. System R is an experimental database management system developed to carry out research on the relational model of data. System R was designed and built by members of the IBM San Jose Research Laboratory.