One of the key developments in data base technology in recent years has been the introduction of the relation as a model for a data base and its manipulation language. This article begins with a very brief discussion of this concept particularly as it relates to the interlinking of file entries. The bulk of the paper addresses the difficult problem of efficiently implementing relational selection criteria and proposes a technique for handling a subset of these retrieval requests. The suggested scheme is sufficiently modular to admit the use of a wide variety of storage structures and search strategies. The method has been implemented and example results of experiments with the technique are presented.