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\title{CoBase: A Cooperative Database System}

\author{Wesley W. Chu, Qiming Chen and Matthew Merzbacher \\
Computer Science Department \\
University of California at Los Angeles \\
}

\begin{document}

\maketitle


\begin{abstract}
This chapter proposes the use of the {\em type abstraction hierarchy
(TAH)} as a framework for deriving {\em cooperative query answers}
(CQA).  The TAH integrates abstraction with the subsumption (is-a) and
composition (part-of) semantics found in the type hierarchy. This
framework provides a multi-level object representation that is an
important aspect of cooperative query answering.  {\em Patterns},
which specify one or more conditions on an object, are introduced as a
small granularity structure with specific semantic information.
Cooperative query answering uses the TAH and patterns to provide query
relaxation, generalization and specialization.  Relaxation can be
explicitly controlled by the user, implicitly performed by the system,
or both.  An explanation system is also included to present the
relaxation path as well as a nearness measure between the approximate
answer and the exact answer.

The operations required for CQA may be added to any conventional query 
language.  As an example, we present {\em CSQL}, a cooperative extension 
of SQL used in the CoBase 
project at UCLA.
Experimental results reveal that the
proposed type abstraction hierarchy and relaxation control provide an
organized structure for representing concepts at
different knowledge levels in various domains, and 
offers a systematic and efficient method for cooperative
query answering.
\end{abstract}

{\em Index Terms}: 
Knowledge Representation,
Type Hierarchy,
Type Abstraction Hierarchy,
Query Language,
Query Rewrite,
Cooperative Query Answering,
Semantic Distance,
Relaxation Control

\htmladdnormallink{View the Paper (requiring a postscript viewer)}
{http://burton.cs.ucla.edu/tech-docs/cqa.ps}

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