61 research outputs found
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 generationĂ¢ 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
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