NIST Special Publication 500-188 Computer Systems Guide to Expert System Technology Building Tools for U.S. DEPARTMENT OF COMMERCE Microcomputers National Institute of Standards and Technology Christopher E. Dabrowski Nisr EHzabeth N. Fong NATL INST OF STAND S TECH R.I.C- REFERENCE N!ST I f PUBLICATIONS -QC 100 .U57 //500-188 1991 mi NIST Special Publication 500-188 /p/'/( 7^ Guide to Expert System Building Tools for Microcomputers Christopher E. Dabrowski EHzabeth N. Fong Computer Systems Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 July 1991 U.S. DEPARTMENT OF COMMERCE Robert A. Mosbacher, Secretary NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY John W. Lyons, Director Reports on Computer Systems Technology The National Institute of Standards and Technology (NIST) has a unique responsibility for computer systenns technology within the Federal government. NIST's Computer Systems Laboratory (CSL) devel- ops standards and guidelines, provides technical assistance, and conducts research for computers and related telecommunications systems to achieve more effective utilization of Federal information technol- ogy resources. CSL's responsibilities include development of technical, management, physical, and ad- ministrative standards and guidelines for the cost-effective security and privacy of sensitive unclassified information processed in Federal computers. CSL assists agencies in developing security plans and in improving computer security awareness training. This Special Publication 500 series reports CSL re- search and guidelines to Federal agencies as well as to organizations in industry, government, and academia. National Institute of Standards and Technology Special Publication 500-188 Natl. Inst. Stand. Technol. Spec. Publ. 500-188, 147 pages (July 1991) CODEN: NSPUE2 U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1991 PREFACE The Computer Systems Laboratory (CSL) (formerly the Institute for Computer Sciences and Technology (ICST)) within the National Institute of Standards and Technology (NIST) has a mission under Public Law 89-306 (Brooks Act) to promote the "economic and efficient purchase, lease, maintenance, operation, and utilization of automatic data processing equipment by Federal departments and agencies." When a potentially valuable technology first appears, CSL may be involved in research and evaluation. Later on, standardization of the results of this research, in cooperation with voluntary industry standards bodies, may best serve Federal interests. Finally, CSL helps Federal agencies make practical use of existing standards and technology through consulting services and the development of supporting guidelines and software. This report provides system managers, planners, and potential expert system developers with a readable description of expert system building tools for the microcomputer environment. Certain commercial software products and companies are identified in this report. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the products identified are necessarily the best available for the purpose. iii ACKNOWLEDGMENTS The technical work for this report was done through extensive review of published literature and hands-on analysis of commercial expert system building tools. We would like to thank the vendors for their cooperation and for their donation of these tools to the CSL Knowledge-Based Systems Laboratory. We would also like to acknowledge the contributions of David Jefferson, Steven Ray, Daniel Benigni, Joseph Collica, and Bruce Rosen, of NIST who reviewed earlier versions of this paper and provided valuable advice. Candy Leatherman and Jennifer Lindeman proofread the document and helped with preparing figures and tables. Special thanks is also due to Steven Oxman, whose advice in preparing the final version of this report was particularly valuable. We also wish to express appreciation to Kenneth Reddy who provided programming assistance during the analysis and evaluation of tools. v ABSTRACT Microcomputer-based expert system building tools (microcomputer-based ESBTs) , sometimes known as expert system shells, are software packages for development of expert systems that run on microcomputers. This report provides system managers, planners, and potential expert system developers with a readable description of ESBTs for microcomputers including a detailed description of specific tool features and the capabilities they support. The technical content of this report is based on analysis of commercially available ESBTs. However, individual commercial products are not described, compared, or ranked. Keywords: artificial intelligence; expert system; expert system building tool; expert system shell; inference; knowledge base; knowledge-based system; knowledge engineering; knowledge representation; microcomputer; object-oriented programming; production rule. vii TABLE OF CONTENTS 1. INTRODUCTION 1 1.1 Motivation 1 1.2 Scope 2 1.3 Organization 3 1 . 4 How to Read This Report 4 2. EXPERT SYSTEM CONCEPTS . 7 2 . 1 Background and History 7 2.2 What Are Expert Systems? 8 2 . 3 The Role of Heuristic Knowledge 9 2.4 The Elements of an Expert System 10 2.4.1 The Knowledge Base 11 2.4.2 The Inference Engine 12 2.4.3 Expert System Interfaces 14 2.5 Differences Between Expert System Programs and Conventional Computer Software 14 2.6 The Role of Expert System Building Tools 15 3. EXPERT SYSTEMS IN OPERATION 17 3 . 1 The Need for Expert Systems 17 3.2 An Example of an Expert System 18 3 . 3 How an Expert System Solves a Problem 19 3.3.1 Use of an Inference Strategy 19 3.3.2 Arriving at a Solution 19 3.4 Expert Systems and Problem Complexity 2 2 3.5 How Expert Systems Explain Their Actions 2 3 3.6 Interfacing Expert Systems to Other Software . 24 3.7 Embedded Expert Systems .... 27 4. APPLICATIONS OF EXPERT SYSTEM TECHNOLOGY 2 9 4.1 Classes of Expert System Applications 29 4.1.1 Expert Systems That Select Solutions .... 29 4.1.2 Expert Systems That Construct Solutions . 3 0 4.1.3 Selection vs. Construction in the Microcomputer Environment 31 4.2 Deploying Expert Systems Within the Organization . 32 4.3 Characteristics of Appropriate Problems 3 2 4.4 Characteristics of Knowledge Used to Solve the Problem 3 3 4.5 The Scope and Size of the Problem 34 4.6 The Source of Expertise 34 4.7 Areas to Avoid 3 5 4 . 8 Summary and Further Sources 3 6 5. DEVELOPING EXPERT SYSTEMS 3 7 5.1 The Expert Systems Development Paradigm 3 7 5.2 Stages of Development 3 9 5.3 The Domain Expert as System Developer 4 0 5.4 General Categories of Software for Expert Systems Development ...... 41 ix 5.5 Differences Between ESBTs and Programming Languages .......... 42 6. ANALYZING MICROCOMPUTER-BASED EXPERT SYSTEMS BUILDING TOOLS 45 6.1 General Categories of ESBTs 45 6.2 Contrasting and Comparing Categories of ESBTs ... 46 6.3 The "Downscaling" of ESBT Capabilities 47 6.4 The ESBT Architecture and Its Major Features ... 48 6.5 Criteria for Analyzing ESBT Features 51 7. FEATURES OF THE DEVELOPER INTERFACE 53 7.1 Knowledge Entry Facilities 53 7.2 Features for Knowledge Base Analysis 55 7.2.1 Facilities for Syntactic Analysis During Program Compilation 55 7.2.2 Facilities for Analyzing Structure of Knowledge Bases 56 7.2.3 Facilities for Analyzing Execution of Expert Systems 57 7.3 A Typical Development Session Using an ESBT ... 58 7.4 Learning to Use an ESBT 59 7.5 The Development Interface and Application Prototyping 60 7.6 ESBTs and Long-term Maintenance of Knowledge Bases 61 7.7 Summary of Development Interface Features 62 8. SUPPORT FOR BASIC INFERENCE CAPABILITIES 65 8.1 Backward Chaining 65 8.1.1 The Backward Chaining Process 65 8.1.2 Supporting Search in Backward Chaining Systems 67 8.1.3 Control Knowledge 70 8.2 Forward Chaining ...... 71 8.2.1 The Forward Chaining Process 71 8.2.2 An Example of Forward Chaining 72 8.2.3 Supporting Search in Forward Chaining Systems 75 - 8.2.4 Daemons 75 8.3 Other Inference Strategies Supported by ESBTs ... 76 8.4 Support for Reasoning Under Uncertainty 77 ' 8.4.1 Certainty Factors . 77 8.4.2 Other Methods for Reasoning About Uncertainty 78 8.5 Inductive Systems 79 . _ 8.6 Analysis of ESBT Inference Capabilities 82 8.7 Summary of Features Supporting Inference },:;. Capabilities ,: , 83 X 9. SUPPORT FOR KNOWLEDGE REPRESENTATION 8 5 9.1 Production Rules That Use Simple Variables .... 86 9.2 Representing Complex Information 87 9.2.1 Basic Structures Supported by ESBTs .... 88 9.2.2 Defining Generic Types of Structures .... 89 9.3 Production Rules and Complex Information 90 9.3.1 Patterns 9 0 9.3.2 Pattern Matching in Production Rules .... 91 9.3.3 The Power of Pattern Matching 92 9.3.4 Pattern Matching and Forward Chaining ... 93 9.3.5 Pattern Matching and Backward Chaining ... 94 9.4 Representing Knowledge in Frames 9 5 9.4.1 Capabilities Supported by Frame Systems . 95 9.4.2 Generalization/Specialization Hierarchies . 96 9.4.3 Integrating Rules and Frames 98 9.4.4 Analysis of Frame Systems and ESBTs .... 99 9.5 ESBTs and Object-Oriented Programming 99 9.5.1 Summary of Features of Object Systems ... 99 9.5.2 Analysis of Object Systems 100 9.6 Summary of Features for Knowledge Representation . 101 10. FEATURES FOR CONSTRUCTING END USER INTERFACES 105 10.1 Features of Simple End User Interfaces 105 10.2 Constructing Advanced End User Interfaces .... 107 10.2.1 Advanced Features Currently Available . 108 10.2.2 Using Advanced User Interface Construction Facilities 109 10.3 Hypertext 110 10.4 Explanation Generation Facilities 110 10.5 Summary of End User Interface Construction Features Ill 11. SUPPORT FOR CONSTRUCTING INTERFACES TO OTHER SOFTWARE SYSTEMS 113 11.1 Interfaces to Microcomputer DBMSs 114 11.2 Interfaces to Procedural Programming Languages . 115 11.3 Interfaces to Other Microcomputer-Based Software . 116 11.4 Accessing Remote Software Systems 117 11.5 Support for Development of Embedded Expert Systems 118 11.6 ESBTs and Application Portability 119 11.7 Summary of External Interface Construction Features 119 12.