Evaluating inter-entry retrieval expressions in a relational data base management system

Among the most important current concepts in data base technology is the relational model of data base management. The theory was introduced by Codd in 1970 and has since been expanded in a large number of articles by Codd, and other authors, for example. The relational concept models the user view of a data base. As a user view it offers many applications significant advantages over more traditional approaches such as that proposed by the CODASYL Data Base Task Group. Unfortunately some of the desirable properties of the relational model, and in particular the very important attribute called data independence, make the concept difficult to implement efficiently. This paper will describe an approach to solving one of the key implementation problems. The concepts discussed here have been embodied in an experimental system called DAMAS developed at the Massachusetts Institute of Technology. A complete discussion of DAMAS can be found in Reference 12.