During the last three or four years several investigators have been exploring “semantic models ” for formatted databases. The intent is to capture (in a more or less formal way) more of the meaning of the data so that database design can become more systematic and the database system itself can behave more intelligently. Two major thrusts are clear: (I) the search for meaningful units that are as small as possible--atomic semantics; (2) the search for meaningful units that are larger than the usual n-ary relation-molecular semantics. In this paper we propose extensions to the relational model to support certain atomic and molecular semantics. These extensions represent a synthesis of many ideas from the published work in semantic modeling plus the introduction of new rules for insertion, update, and deletion, as well as new algebraic operators.

Sound naming schemes for objects are crucial in many parts of computer science, such as database modeling, database implementation, distributed and federated databases, and networked and distributed operating systems. Over the past 20 years, physical pointers, keys, surrogates and object identifiers have been used as naming schemes in database systems and elsewhere. However, there are some persistent confusions about the nature, applicability and limits of these schemes. In this paper we give a detailed comparison of three naming schemes, viz. object identifiers, internal identifiers (often called surrogates) and keys. We discuss several ways in which identification schemes can be implemented, and show what the theoretical and practical limits of applicability of identification schemes are, independently from how they are implemented. In particular, we discuss problems with the recognition and authentication of identifiers. If the identified objects are persons, an additional problem is that object identification may conflict with privacy demands; for this case, we indicate a way in which identification can be combined with privacy protection.

A new kind of implementation technique for access paths connecting sets of tuples qualified by attribute values is described. It combines the advantages of pointer chain and multilevel index implementation techniques. Compared to these structures the generalized access path structure is at least competitive in performing retrieval and update operations, while a considerable storage space saving is gained. Some additional features of this structure support m-way joins and the evaluation of multirelation queries, and allow efficient checks of integrity assertions and simple reorganization schemes.