Brought to you by EarthWeb
IT Library Logo

Click Here!
Click Here!

Search the site:
 
EXPERT SEARCH -----
Programming Languages
Databases
Security
Web Services
Network Services
Middleware
Components
Operating Systems
User Interfaces
Groupware & Collaboration
Content Management
Productivity Applications
Hardware
Fun & Games

EarthWeb Direct EarthWeb Direct Fatbrain Auctions Support Source Answers

EarthWeb sites
Crossnodes
Datamation
Developer.com
DICE
EarthWeb.com
EarthWeb Direct
ERP Hub
Gamelan
GoCertify.com
HTMLGoodies
Intranet Journal
IT Knowledge
IT Library
JavaGoodies
JARS
JavaScripts.com
open source IT
RoadCoders
Y2K Info

Previous Table of Contents Next


Chapter 18
Logic

R.G. (Randy) Goebel and Francisco J. Cantu-Ortiz


CONTENTS

1. Introduction
2. Historical Background
3. Logic and Reasoning
3.1. Deduction
3.1.1. Propositional Logic
    3.1.2. First-Order Logic
    3.1.3. Higher-Order Logic
3.2. Nonclassical Logics
3.2.1. Nonmonotonic Reasoning
3.3 Probabilistic Reasoning
3.4. Induction
3.5. Abduction
4. Logical Reasoning Systems
4.1. Rule-Based Systems
4.2. Logic Programming Systems and Theorem Provers
4.3. Semantic Networks and Frame Systems
4.4. Case-Based Systems
4.5. Meta-Level Reasoning
5. Research Issues
6. Future Trends and Summary
Acknowledgments
References

1. INTRODUCTION

Logic has had great influence on the development of expert systems, but its role has often been implicit rather than explicit, and that influence has not always been clearly described or understood. One reason is that the concept of logic is quite broad, and it is sometimes difficult to keep all of its important aspects in mind when considering the role and use of logic in knowledge-based systems applications. Another reason is that logic was originally developed as an abstract description of reasoning, and has only recently been widely adapted for use as a computational system.

As stated by a pioneer of using logic for computation, Alan Robinson has described logic as "the science of what follows from what." In other words, logic is about what kinds of conclusions can be reasonably drawn from what one already knows.

Even on the basis of that informal (but concise!) definition, the relationship to expert systems is clear. Logic provides a tool for both the analysis of expert reasoning, and for the articulation and use of what is known about a problem for which expertise is required: logic is about the relationship between what is known, and how what is known can be deployed to reason about problems and situations.

To understand logic and its role in expert systems is to first dispel some of the many misconceptions about logic. One is that logic is only about reasoning. The fault behind that misconception is that one cannot practically reason without knowing about something. Even the simplest syllogisms are little more than syntactically obvious without interpretation: "All men are mortal; Socrates is a man, therefore Socrates is mortal," is much more instructive than the relatively sterile "A implies B; A, therefore B."

Similarly, logic is not preoccupied with syntax, or the form in which what one knows is expressed. This misconception arises only when one misconstrues the particular form of knowledge with the reasoning itself. For example, it has been typical to misconstrue the conclusion that A is above B in the simple diagram

A

B

as a kind of reasoning distinct from that within the purview of logic. This is a misconception that arises from confusing the immediately apparent form of the information, in this case as encoded in two dimensions. However, the essence of logic is independent of the form in which information to be reasoned about is represented. Logic requires only that there is some more-or-less conventional way of representing information, and that there is some conventional way of using it.


Previous Table of Contents Next

footer nav
Use of this site is subject certain Terms & Conditions.
Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Please read our privacy policy for details.