Expert Systems


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  • We often talk of expert. But, what is the expert. Here, we give its definition:( 念 PPT). And, what is Expert System? Until now, no unified definition has been given. I’ll give several kinds of definitions later on. Then, what is Knowledge-based system? Because…( 念 PPT)
  • Here just are several kinds of definitions of Expert system. ( 念 PPT)
  • This is the Architecture of an ideal expert system. We can see: it is composed of 5 parts: Knowledge Base; Reasoning Machine; Communication Interface; Interpreter; and Blackboard. And what is their usage? First, …( 念 ppt); Sencond, …( 念 PPT); …… ( 最后 ) However, we must take note here:( 点图下方标注 , 念 PPT)
  • ( 最后 )The Blackboard, we mentioned just now, is really a global database.
  • mediate [midieit] 调节
  • Now, we’ll study how to build a Expert System. The key for successfully building an expert system is to begin it from a smaller one, and extend and test it step by step, make it into a larger-scale and more perfect system. ( 念 PPT)
  • Design of the initial knowledge base is the most important and most difficult task. The design involves the following 5 stages: Problem identification( 问题知识化 ); Knowledge conceptualization( 知识概念化 ); Concept formulization( 概念形式化 ); Rule formulation( 形式规则化 ); Rule validation( 规则合法化 ).
  • The Stages for designing initial knowledge base can be shown in this figure. ( 对着 PPT 讲 )
  • Here are some types of Expert System. This is their Category( 指着左边 ), This is the problems they can address. This page, I won’t introduce in detail here, left you to read by yourself after class. OK?
  • Just now, we introduced the Expert System. Now, we will learn the Expert Control System. Before this, we must have a look at the differences between expert systems and expert control systems. ( 念 PPT)
  • There are 2 main types of expert control: The Expert control system and Expert controller. ( 念 PPT)
  • This is a typical structure of Expert Control System. Here, just the Controller. This system should execute following 3 tasks:( 快翻下一页 )
  • ( 对着 PPT 念 )
  • Now, we’ll discuss a specific structure of expert controller, that’s Industrial expert controller. ( 对着书念 ) ( 最后 , 翻开书讲解 )
  • Now, we’ll get a knowledge of a very famous Expert system-MYCIN. ( 念 PPT)
  • 治疗疾病: Cure Disease
  • Neuro-surgery [njuərəu ‘sə:dʒəri] 神经外科
  • Let’s have an analysis about the defects and development trend of MYCIN. ( 念 PPT) Diagnostic [daiəg nɔstik] 诊断的
  • Internist 内科医生
  • Expert Systems

    1. 1. Expert SystemsDirectors : Prof. Zixing Cai &Miss WenShaCentral South UniversityCollege of Information Scienceand Engineering
    2. 2. What is an Expert System?Experts are people who are very familiarwith solving specific types of problems.Expert SystemUntil now, no unified definition has beengiven.Knowledge-based systemThe fundamental function of the expertsystem depends upon its knowledge,therefore, the expert system is sometimes Ccalled knowledge-based system. C IS I Central South University Artificial Intelligence
    3. 3. What is an Expert System(ES)? Definition 1: ES can handle real-world complex problems which need an expert’s interpretation andIn short, an by using a computer model of solve problems ES is an intelligent human expert reasoning to reach the same computer program that can conclusions that the human expert would do if heperform special and difficult task(s) or she faces with a comparable problem. Definition 2: ES is an intelligent computer program in some field(s) at the level of to that uses knowledge and inference procedures human experts. solve problems that are difficult enough to require significant human expertise for their solutions. C IS IC Central South University Artificial Intelligence
    4. 4. Architecture of ideal expert systemUser Communication Knowledge Interface Base Interpreter Plan Planner Agenda Coordinator Solution Adjuster Reasoning Blackboard Machine IS IC Architecture of an ideal expert system C Central South University Artificial Intelligence
    5. 5. ES-Knowledge Base(1)Knowledge Base To store knowledge from the experts ofspecial field(s). It contains facts and feasibleoperators or rules for heuristic planning andproblem solving. The other data is stored in a separatedatabase called global database, ordatabase simply. C IS IC Central South University Artificial Intelligence
    6. 6. ES-Reasoning Machine(2)Reasoning Machine To memorize the reasoning rules and thecontrol strategies applied. According to the information from theknowledge base, the reasoning machine cancoordinate the whole system in a logicalmanner, draw inference and make adecision. C IS IC Central South University Artificial Intelligence
    7. 7. ES- User Interface (3)User Interface To communicate between the user andthe expert system. The user interacts with the expert systemin problem-oriented language such as inrestricted English, graphics or a structureeditor. The interface mediates informationexchanges between the expert system andthe human user. C IS IC Central South University Artificial Intelligence
    8. 8. ES- Interpreter(4)Interpreter Through the user interface, interpreterexplains user questions, commands andother information generated by the expertsystem, including answers to questions,explanations and justifications for itsbehavior, and requests for data. C IS IC Central South University Artificial Intelligence
    9. 9. ES-Blackboard (5)Blackboard To record intermediate hypotheses anddecisions that the expert systemmanipulates. C IS IC Central South University Artificial Intelligence
    10. 10. ES-NoteNote: Almost no exiting expert system containsall the components shown above, but somecomponents, especially the knowledge baseand reasoning machine, occur in almost allexpert systems. Many ESs use global database in place ofthe blackboard. The global databasecontains information related to specific tasksand the current state. C IS IC Central South University Artificial Intelligence
    11. 11. Building Expert SystemThe key for successfully building an expertsystem is to begin it from a smaller one, andextend and test it step by step, make it intoa larger-scale and more perfect system.The general procedure for building ESs :Design of initial Knowledge BaseDevelopment & test for prototype 原型systemImprovement & induction 归纳 for the C IS ICknowledgeUniversity Artificial Intelligence Central South
    12. 12. Design of initial Knowledge BaseProblem identificationKnowledge conceptualizationConcept formulizationRule formulationRule validation C IS IC Central South University Artificial Intelligence
    13. 13. Stages for Designing KB define key concept of the Re-designment knowledge ,for example : identify what the problem use knowledge change the knowledge to check the type of data structure , is , how to define it , can representation programming language of correctness conditions that have known, we divide it into some sub RefinementsQuestions Knowledge Concepts method to represent can be identified by the goal state, assumption that rules or problems the Structure knowledge. the computer. knowledge and control strategy. Rules Indentifi- Conceptu- Formali- Rule Validation cation alization zation Formalization Concepts Conclusion Representation Stages for designing knowledge base C IS IC Central South University Artificial Intelligence
    14. 14. Types of Expert System (ES) Category Problem AddressedInterpretation Inferring situation descriptions from sensor dataPrediction Inferring likely consequences of given situationDiagnosis Inferring system malfunction from observationDesign Configuring objects under constrainsPlanning Designing actionsMonitoring Comparing observation to plan vulnerabilitiesDebugging Prescribing remedies for malfunctionRepair Executing a plan to administer a prescribed remedyInstruction Diagnosing, debugging and repairing student behaviorControl C IS IC Interpreting, predicting, repairing and monitoring system behavior Central South University Artificial Intelligence
    15. 15. Expert Control SystemsImportant differences between expert systems andexpert control systems:Expert systems simply complete consultativefunction for problems of special domains and aidusers to work.Expert control systems need to make decisions tocontrol action independently and automatically.Expert systems usually work in off-line mode.Expert control systems need to acquire dynamicinformation in on-line mode and make real-timeC IS Icontrol for the system. C Central South University Artificial Intelligence
    16. 16. Two main types of expert control Two main types of expert control: Expert control system With a more complex structure, higher cost, better performance, and used to plants or processes where higher technical requirements are needed. Expert controller With a simpler structure, lower cost and has a performance that can meet the general requirements for the industrial process control. C IS IC Central South University Artificial Intelligence
    17. 17. Structures of Expert Control System Operator InterfaceController Reasoning Machine Domain Date Control Knowledge Base DigitalAlgorithms Processing D/A A/DActuators Process Sensors C A typical structure of expert control system IS IC Central South University Artificial Intelligence
    18. 18. Tasks of Expert Control System The expert control system should execute following tasks: Supervise the operation of the plant (process) and controller. Examine possible failure or fault of the system components, replace these faulty components or revise control algorithms to keep the necessary performance of the system. In special cases, select suitable control algorithm to adapt the variation of the system parameters and environment. S IC CI Central South University Artificial Intelligence
    19. 19. Store the domain knowledge of industrial process control,experience Extract and process of experts(expertise) and Expert Controller Use the forward chaining Sum up every control facts information, provide reasoning to judge the Knowledge Base (KB) pattern and control control strategy and learn conditions of every rule in experience of the adaptation with foundation the sequence controlled process K G Feature e Recognition S Inference I Set of U Y Engine (IE) Control Rules PlantR Information - Processing u Sensor(s) Industrial expert controller C IS IC Central South University Artificial Intelligence
    20. 20. Expert system-MYCINAn early expert system developed in early1970s at Stanford UniversityWrote by Lisp LanguageAuthor: Bruce G. Buchanan & Edward H.Shortliffe <<Rule-Based Expert Systems: The MYCIN Experiments of the Stanford Heuristic Programming Project >>This expert system was designed to identifybacteria causing severe infections C IS IC Central South University Artificial Intelligence
    21. 21. C IS ICCentral South University Artificial Intelligence
    22. 22. Reasoning & Problem solving strategyMYCIN could use backward chaining to find outwhether a possible bacteria was to blame.“Certainty factor” is used for an assessment of thelikelihood 可能性评估 of one bacteria.MYCIN’s problem solving strategy was simple: For each possible bacteria: Using backward chaining, try to prove that it is the case, finding the certainty. Find a treatment which ” covers” all the bacteria above some level of certainty. IC CIS Central South University Artificial Intelligence
    23. 23. MYCIN: Problem SolvingWhen trying to prove a goal through backwardchaining, system could ask user certain questions.Certain facts are marked as “askable”, so if theycouldn’t be proved, ask the user.The ask procedure is carried out in following styleof dialogue: MYCIN: Has the patient had neurosurgery? USER: No. MYCIN: IS the patient a burn patient? USER: No. … MYCIN: It could be Diplococcus.. C IS IC Central South University Artificial Intelligence
    24. 24. Modeling Human Diagnostic StrategiesProblem Solving Strategy used in MYCINonly works when small number ofhypotheses (e.g., bacteria).For hundreds of possible diseases, need abetter strategy.Later medical diagnostic systems used anapproach based on human expertreasoning. C IS IC Central South University Artificial Intelligence
    25. 25. Diagnostic Reasoning: InternistInternist is a medical expert system forgeneral disease diagnosis.Knowledge in system consists of diseaseprofiles 概况 , giving symptoms 症状 associatedwith disease and strength of association. C IS IC Central South University Artificial Intelligence
    26. 26. Problem Solving in InternistUse initial data (symptoms) to suggest, or trigger 引发 possible diseases.Determine what other symptoms would beexpected to confirm these diseases.Gather more data to differentiate 区分 betweenthese hypotheses. Either: If one hypothesis most likely, try to confirm it. If many possible hypotheses, try to throw some out. If a few hypotheses, try to discriminate 区别 between IS IC them. C Central South University Artificial Intelligence
    27. 27. Medical Expert Systems TodayMedical expert systems were quite effective inevaluations comparing their performance withhuman experts.Support the physicians 医生 decisions, rather thandoing the whole diagnosis.Include many useful support materials 辅助材料 , suchas report generating tools, reference material etc. C IS IC Central South University Artificial Intelligence
    28. 28. Summary: Expert SystemsEffective systems have been developed thatcapture expert knowledge in areas like medicine.Typically combine rule-based approaches, withadditional certainty/probabalistic reasoning, andsome top level control of the problem solvingprocess.Not a huge take-up of systems, perhaps due tofailure to adequately consider how they would beintegrated into current practice. C IS IC Central South University Artificial Intelligence
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