FUNCTIONAL DEPENDENCIES AND INCOMPLETE INFORMATION

Functional dependencies play an important role in relational database design. They are defined in the context of a single relation which at all times must contain tuples with non-null entries. In this paper we examine an extension of the functional dependency interpretation to handle null values, that is, entries in tuples that represent incomplete information in a relational database. A complete axiomatization of inference rules for extended functional dependencies is also presented. Only after having such results is it possible to talk about decompositions and normalization theory in a context of incomplete information. Finally, we show that there are several practical advantages in using nulls and a weaker notion of constraint satisfiability.Information Systems Working Papers Serie

CHOOSING A DATABASE QUERY LANGUAGE

A methodology is presented for selecting query languages suitable for certain user types. The method is based on a trend model of query language development on the dimensions of functional capabilities and usability. Expected developments are exemplified by the description of "second generationâ database query languages. From the trend model are derived: a classification scheme for query languages; a criterion hierarchy for query language evaluation; a comprehensive classification scheme of query language users and their requirements; and recommendations for allocating language classes to user types. The method integrates the results of existing human factors studies and provides a structured framework for future research.Information Systems Working Papers Serie

COUPLING EXPERT SYSTEMS WITH DATABASE MANAGEMENT SYSTEMS

The combined use of Database Management Systems (DBMS) and Artificial Intelligence-based Expert Systems (ES) is potentially very valuable for modern business applications. The large body of facts usually required in business information systems can be made available to an ES through an existing commercial DBMS. Furthermore, the DBMS itself can be used more intelligently and operated more efficiently if enhanced with ES features. However, the implementation of a DBMS-ES cooperation is very difficult. We explore practical benefits of the cooperative use of DBMS and ES, as well as the research challenges it presents. Strategies for providing data from a DBMS to an ES are given; complementary strategies for providing intelligence from an ES to a DBMS are also presented. Finally, we discuss architechural issues such as degree of coupling, and combination with quantitative methods. As an illustration, a research effort at New York University to integrate a logic-based business ES with a relational DBMS is described.Information Systems Working Papers Serie

QUERY LANGUAGES - A TAXONOMY

Information Systems Working Papers Serie

DBMS TRANSACTION TRANSLATION

Data translation and transaction translation are two major problems that have to be solved in order to achieve the coexistence of heterogeneous distributed databases. In this paper we discuss the problem of transaction translation. The nature of the problem is explored by developing direct translations of transactions between the relational and hierarchical and network models. Methods for mapping a hierarchical or network schema to an equivalent relational schema are presented. The relational operators projection, selection, join, insertion. deletion and update are translated to equivalent hierarchical and network operations.Information Systems Working Papers Serie

DATABASE ACCESS REQUIREMENTS OF KNOWLEDGE-BASED SYSTEMS

Knowledge bases constitute the core of those Artificial Intelligence programs which have come to be known as Expert Systems. An examination of the most dominant knowledge representation schemes used in these systems reveals that a knowledge base can, and possibly should, be described at several levels using different schemes, including those traditionally used in operational databases. This chapter provides evidence that solutions to the organization and access problem for very large knowledge bases require the employment of appropriate database management methods, at least for the lowest level of description -- the facts or data. We identify the database access requirements of knowledge-based or expert systems and then present four general architectural strategies for the design of expert systems that interact with databases, together with specific recommendations for their suitability in particular situations. An implementation of the most advanced and ambitious of these strategies is then discussed in some detail.Information Systems Working Papers Serie

A SHORT INTRODUCTION TO EXPERT SYSTEMS

Information Systems Working Papers Serie

STUDIES IN THE EVALUATION OF A DOMAIN-INDEPENDENT NATURAL LANGUAGE QUERY SYSTEM

There is growing consensus that some of the most crucial questions concerning the feasibility and desirability of natural language interfaces to databases can only be resolved by empirical research. This paper reports the results of several empirical studies which investigated the same domain-independent natural language query system, using various applications in two different natural languages - English and German. Taken together, these experiments involved about 100 subjects and over 12,000 queries, constituting the bulk of empirical evaluations of natural query language systems reported to date. Some definitive results are derived from the combined experience, and plans are outlined to resolve several of the remaining issues.Information Systems Working Papers Serie

ACCESS TO SPECIFIC DECLARATIVE KNOWLEDGE BY EXPERT SYSTEMS: THE IMPACT OF LOGIC PROGRAMMING

As part of the operation of an Expert System, a deductive component accesses a database of facts to help simulate the behavior of a human expert in a particular problem domain. The nature of this access is examined, and four access strategies are identified. Features of each of these strategies are addressed within the framework of a Logic-based deductive component and the relational model of data.Information Systems Working Papers Serie