Topic_2B_Expert_Systems.ppt - ICT619 Intelligent Systems Topic 2 Expert Systems Expert Systems PART A(last week Introduction Applications of expert

Topic_2B_Expert_Systems.ppt - ICT619 Intelligent Systems...

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Unformatted text preview: ICT619 Intelligent Systems Topic 2: Expert Systems Expert Systems PART A (last week) Introduction Applications of expert systems Structure of an expert system An example rule base Reasoning in a rule-based expert system Reasoning using forward and backward chaining Dealing with uncertainty PART B Frame-based expert systems Developing expert systems Advantages and disadvantages of expert systems Case studies ICT619 2 PART B Frame-based expert systems Developing expert systems Advantages and disadvantages of expert systems Case Studies ICT619 3 Frame-based expert systems – what is a frame? (Negnevitsky, 2005) A frame is a data structure with typical knowledge about a particular object or concept. Frames were first proposed by Marvin Minsky in the 1970s. Each frame has its own name and a set of attributes associated with it. Carrier, Name, Flight, Date, … Gate are slots in the frame Boarding pass. ICT619 4 Frame-based expert systems – what is a frame? (cont’d) Frames provide a natural, concise way to represent knowledge. Frames are an early application of object-oriented programming for expert systems. A knowledge engineer refers to, what is an equivalent of an object in OOP, as a frame ICT619 5 Object-oriented Programming Object-Oriented Programming (OOP) is a programming method that uses instances (known as objects) of different classes of entities for problem solving A class in OOP defines an abstraction of entities with a common set of characteristics (attributes) and behaviours An example of an attribute is a variable type such as a string. An entity ('message') might have an attribute ('type::string') with value ("Hello to everybody listening!"). Or an entity ('cat') might have an attribute ('colour') with value ('white') Entities often have a list of attribute-value pairs Behaviours are represented by procedures applicable to objects of that class (called methods in OOP). ICT619 6 Frames as a knowledge representation technique The concept of a frame is defined by a collection of slots. Each slot describes a particular attribute or operation of the frame. Slots are used to store values. A slot may contain a default value, a pointer to another frame, a set of rules or procedure by which the slot value is computed. Such procedures are executed only when the slot in which they sit is accessed ICT619 7 Classes and instances A group of similar objects belong to a class The word frame may refer to a particular object or instance of a class To be more precise, a class-frame describes a group of objects with common attributes. Instance-frame refers to a particular object - Animal, person, car and computer are all class-frames. - Mammal, Jane Doe, Toyota, Dell Inspiron are all instance-frames. Frame-based systems are characterized by inheritance. Inheritance is the process by which all characteristics of a classframe are assumed by an instance-frame as well as any sub-classes. ICT619 8 A Class Frame CLASS: [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [N] [Str] Computer Item Code: Model: Processor: Memory: Hard Drive: Floppy: CD-ROM: Mouse: Keyboard: Power Supply: Warranty: Cost: Stock: [Default] 3.5”; 1.44MB [Default] [Default] 145 Watt 3 years [Initial] In stock ICT619 9 Two Instance Frames INSTANCE: IBM Aptiva S35 INSTANCE: IBM Aptiva S9C Class: [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [N] [Str] Class: [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [Str] [N] [Str] Computer Item Code: SY7973 Model: IBM Aptiva S35 Processor: Pentium 233MHz Memory: 48MB Hard Drive: 6.4GB Floppy: 3.5"; 1.44MB CD-ROM: 24X Mouse: Cordless Mouse Keyboard: 104-key Power Supply: 145 Watt Warranty: 3 years Cost: 1199.99 Stock: In stock ICT619 Computer Item Code: SY7975 Model: IBM S9C Processor: Pentium 200MHz Memory: 32MB Hard Drive: 4.2GB Floppy: 3.5"; 1.44MB CD-ROM: 16X Mouse: 2-button mouse Keyboard: 104-key Power Supply: 145 Watt Warranty: 3 years Cost: 999.99 Stock: In stock 10 Methods and Demons Expert systems are required not only to store the knowledge but also to validate and manipulate this knowledge. To add actions to frames, a procedures is associated with a frame attribute that is executed whenever requested. Frame procedures are known as methods and demons Demons are limited to IF-THEN statements, but methods can be more complex. ICT619 11 Methods and Demons (cont’d) Most frame-based expert systems use two types of methods: WHEN NEEDED and WHEN CHANGED A WHEN NEEDED method is executed when information associated with a particular attribute is needed for solving the problem, but the attribute value is undetermined. A WHEN CHANGED method is executed immediately when the value of its attribute changes. The following simple example illustrates the use of WHEN CHANGED methods in a class at run-time. ICT619 12 An ES to assist a loan officer in evaluating credit requests from small business ventures A credit request is to be classified into one of three categories, “Give credit”, “Deny credit” or “Consult a superior”. When a loan officer provides a qualitative rating of the expected yield from the loan, the expert system: 1. Compares the business collateral with the amount of credit requested 2. Evaluates a financial rating based on a weighted sum of the business’s net worth to assets last year’s sales growth gross profit on sales and short-term debt to sales 3. Determines a category for the credit request. ICT619 13 Input display for the request selection Credit Evaluation Advisor Requested credit 50000 Currency deposit 50000 Stocks 9000 Mortgages 12000 List of Requests No CN001-98 CN002-98 CN003-98 CN001-98 Applicant Name Mrs White, J. Mr Black, N. Mr Green, P. Mr Clark, E. Net worth to assets 40 Last year’s sales growth 20 Gross profit on sales 45 Previous Next 9 First Last Short-term debt to sales Expected yeld Excellent The Credit Evaluation Advisor has determined the category of the credit request as Evaluate Credit Collateral Excellent Financial rating Help Give Credit Good Restart Exit ICT619 14 The class Action Data and WHEN CHANGED methods CLASS: Action Data [S] Goto Next: [WHEN CHANGED] [S] Goto Previous: [WHEN CHANGED] [S] Goto First: [WHEN CHANGED] [S] Goto Last: [WHEN CHANGED] INSTANCE: Action Data 1 Class: Action Data [S] Goto Next: TRUE [S] Goto Previous: UNDETERMINED [S] Goto First: UNDETERMINED [S] Goto Last: UNDETERMINED WHEN CHANGED BEGIN Current Request Number := Request Number OF Request FIND Request LIMIT 1 WHERE Request Number OF Request > Current Request Number FIND END END WHEN CHANGED BEGIN Target Request Number := Request Number OF Request - 1 IF Target Request Number > 0 THEN BEGIN FIND Request LIMIT 1 WHERE Request Number OF Request = Target Request Number FIND END END END WHEN CHANGED BEGIN FIND Request LIMIT 1 FIND END END WHEN CHANGED BEGIN Target Request Number := Total Number of Requests FIND Request LIMIT 1 WHERE Request Number OF Request = Target Request Number FIND END END ICT619 ICT619 15 Class Request CLASS: Request [Str] Applicant’s name: [Str] Application no.: [N] Requested credit: [N] Currency deposits: [N] Stocks: [N] Mortgages: [N] Net worth to assets: [N] Last year's sales growth: [N] Gross profits on sales: [N] Short-term debt to sales: [C] Expected yield Excellent: Reasonable: Poor: [N] Request Number: ICT619 16 Instances of the Class Request INSTANCE: Request 1 Class: Request [Str] Applicant’s name: Mrs White, J. [Str] Application no.: CN001-98 [N] Requested credit: 50000 [N] Currency deposits: 50000 [N] Stocks: 9000 [N] Mortgages: 12000 [N] Net worth to assets: 40 [N] Last year's sales growth: 20 [N] Gross profits on sales: 45 [N] Short-term debt to sales: 9 [C] Expected yield Excellent: TRUE Reasonable: FALSE Poor: FALSE [N] Request Number: 1 INSTANCE: Request 2 Class: Request [Str] Applicant’s name: Mr Black, N. [Str] Application no.: CN002-98 [N] Requested credit: 75000 [N] Currency deposits: 45000 [N] Stocks: 10000 [N] Mortgages: 20000 [N] Net worth to assets: 45 [N] Last year's sales growth: 25 [N] Gross profits on sales: 35 [N] Short-term debt to sales: 10 [C] Expected yield Excellent: FALSE Reasonable: TRUE Poor: FALSE [N] Request Number: 2 ICT619 17 Inference in a frame-based system Most frame-based expert systems allow the use of a set of rules to evaluate information contained in frames. Similar to a goal-driven rule-based system, the inference engine in a frame-based system also searches for the goal. But rules in such a system play an auxiliary role. Frames represent here a major source of knowledge, and both methods and demons are used to add actions to the frames. Thus, the goal in a frame-based system can be established either in a method or in a demon. ICT619 18 Example: Evaluation of credit request The expert system is expected to begin the evaluation when the user clicks the Evaluate Credit pushbutton on the input display. This pushbutton is attached to the attribute Evaluate Credit of the class Credit Evaluation. ICT619 19 The Credit Evaluation class, WHEN CHANGED and WHEN NEEDED methods CLASS: Credit Evaluation [S] Evaluate Credit: [WHEN CHANGED] [C] Collateral: Excellent: Good: Moderate: [C] Financial rating: Excellent: Good: Medium: Bad: [C] Evaluation: [WHEN NEEDED] Give credit: Deny credit: Consult a superior: WHEN CHANGED BEGIN PURSUE Evaluation OF Credit Evaluation END WHEN NEEDED BEGIN Evaluation OF Credit Evaluation IS Consult superior := TRUE END ICT619 20 The rule-base RULE 1 IF Currency deposits OF Request >= Requested credit OF Request THEN Collateral OF Credit Evaluation IS Excellent RULE 2 IF Currency deposits OF Request >= Requested credit OF Request * 0.7 AND (Currency deposits OF Request + Stocks OF Request) >= Requested credit OF Request THEN Collateral OF Credit Evaluation IS Excellent RULE 3 IF (Currency deposits OF Request + Stocks OF Request) > Requested credit OF Request * 0.6 AND (Currency deposits OF Request + Stocks OF Request) < Requested credit OF Request * 0.7 AND (Currency deposits OF Request + Stocks OF Request + Mortgages OF Request) >= Requested credit OF Request THEN Collateral OF Credit Evaluation IS Good RULE 4 IF (Currency deposits OF Request + Stocks OF Request + Mortgages OF Request) <= Requested credit OF Request THEN Collateral OF Credit Evaluation IS Moderate RULE 5 IF Net worth to assets OF Request * 5 + Last year's sales growth OF Request + Gross profits on sales OF Request * 5 + Short term debt to sales OF Request *ICT619 2 <= -500 21 THEN Financial rating OF Credit Evaluation IS Bad Example: Evaluation of credit request (cont’d) The WHEN NEEDED method attached to the attribute Evaluation is used to establish its value. The inference engine executes this method when it needs to determine the value of Evaluation. If based on the set of rules provided for credit evaluation, the inference engine cannot establish the value of the attribute Evaluation, the attribute Evaluation receives the value Consult a superior. The task of developing a frame-based ES can be difficult for the knowledge engineer due to the complexity of inheritance. ICT619 22 Developing an expert system - issues to be considered Does the task require knowledge available from human experts? Are human experts too expensive and scarce? Is the problem domain well-structured? Problem domain must be well-defined and formalised. Amount of knowledge required to solve such problems should not be "too large". No commonsense reasoning (that can't be reduced to rules) Can the problem be solved by traditional computing methods? Numerical, statistical or operations research methods, if applicable, are likely to do better than heuristic solution Are cooperative, articulate and enthusiastic human experts available? Expert can articulate reasoning process with a high degree of confidence Expert convinced of the benefit of the ES, and does not feel threatened Expert has the time ICT619 23 Developing an expert system - issues (cont’d) Adequate management support (expert's boss has to be on board) How big and complex is the problem? Available technology must be able to handle required knowledge base efficiently Is development cost justified by returns? Is the solution found likely to remain valuable for several years to come? The cost (and availability) of the human expert needs to be compared with the cost of developing the ES Cost can be reduced by development tools like ES shells Will there be adequate infrastructure and management support for ES maintenance in future? ICT619 24 Developing an expert system - the people 1. The knowledge group (knowledge engineer + the domain expert) 2. The developer group 3. The user group Knowledge engineer Usually a system analyst with background in AI extracts knowledge from domain expert and formalizes it into a knowledge base decides on the knowledge representation scheme strategies for reasoning and searching the knowledge base design of the user interface. hardware and software. ICT619 25 Knowledge engineer (cont’d) May not initially have any experience of the ES problem domain (but tends to learn some during the project) Sessions with the domain expert are the usual method used for knowledge gathering Machine learning techniques such as decision trees (subject of a later topic) can also be used Time taken by knowledge acquisition process – approx. 60 to 70% of overall ES development time ICT619 26 The Developer and User groups The developer group Implements the expert system in close cooperation with the knowledge group and the user group. Either programs the system from scratch or makes use of existing software products like an expert system shell The user group Can be a regular user, eg, an employee of the organization May be an irregular user such as bank customer Needs and characteristics of both categories of users need to be taken into account, particularly for the user interface design. The user must feel confident and happy with the system So a usability evaluation should be conducted with these people ICT619 27 The expert system development cycle Development strategy Early prototyping and incremental development Mistakes found during development lead to correction and addition to the knowledge base Steps usually followed: 1. Knowledge engineer gains familiarity with the problem domain 2. Knowledge engineer and domain expert start knowledge extraction (knowledge elicitation) process Difficult because Experts don't know how they know Experts may disagree Experts may be wrong, or fuzzy on details ICT619 28 The expert system development cycle (cont’d) 3. Knowledge engineer decides on representation scheme, search strategy, user interface 4. Prototype built 5. Knowledge engineer and domain expert test prototype, corrects, refines and redesigns if necessary 6. Final version built and evaluated. ES knowledge base must be continuously updated by adding, deleting or changing rules to keep up with new knowledge and changed circumstances ICT619 29 Expert system shells A general expert system development product for the market An expert system shell has all components of an expert system -except the knowledge-base User Interface: Knowledgebase editor - Menudriven User - GUI Knowledge-base Inference engine Working memory - Natural language Explanation sub-system ICT619 30 Expert system shells (cont’d) Good shells also provide facilities for communication with external sources including Database management systems Spreadsheets Graphics packages. Shell selected must match reasoning process (goal driven or data driven) characterising given problem domain Other features to be considered knowledge representation scheme and the knowledge base editor user interface explanation capabilities. ICT619 31 Testing expert systems Correctness of ES can not be guaranteed due to its heuristic nature Some test strategies Use of historical data Data on existing cases fed to the system, and the outputs analysed Inconsistency of human decisions taken into account in case of any difference between the data and ES ES against Expert ES tested against the expert by presenting both with hypothetical or actual cases Expert’s reasoning compared with that of the ES to make sure both arrived at the same conclusion for the same reasons ICT619 32 Testing expert systems (cont’d) Field tests Users in the field use the system for a given period of time Favourable results in the field add to ES validity Serious problems in field tests indicate need for further improvement of the design Turing test ES and a human expert are subjected to blind user evaluation User’s failure to differentiate between answers produced by the two enables the ES to pass ICT619 33 Some limitations of expert systems Knowledge acquisition remains the major bottleneck in applying ES technology to new domains. Not adaptive Knowledge engineer responsible for revising and maintaining system. Evaluating expert system correctness is difficult Explanation of an outcome in terms of the reasoning process can be time consuming for large amounts of data ICT619 34 Some limitations of expert systems (cont’d) Self-explanatory individual rules, but difficult to relate to overall strategy due to lack of hierarchy Maintenance and extension of a rule base can be difficult for a relatively large rule base (beyond 100 rules). ES are not as compact as neural network and genetic algorithm systems. This makes them harder to embed in other systems, as the inference engine and working memory must be part of the system at run-time. ICT619 35 Case Studies Case 1: An Expert System for Pattern Directed Data Mining of Point-Of-Sale Data (see Dhar & Stein pp.244-). Objective Supermarkets need to know how different product categories performed over certain periods of time in particular regions and nationally Some experts are able to detect significant trends in these data – what is happening in the market place? A.C. Nielsen wanted to create an expert system with this expertise and make it available to its sales reps ICT619 36 Case 1: An Expert System for Pattern Directed Data Mining Requirements and constraints Enable reps to put together a clear and unambiguous story for their customer Use vocabulary commonly used by sales reps Able to work with Nielsen’s databases Be distributable on low-end PCs to sales reps across the country Reports able to be produced under five minutes\ High explainability to enable reps to construct stories Six months development time – Nielsen wanted to leap frog rival ICT619 37 Case 1: An Expert System for Pattern Directed Data Mining (cont’d) Objectives and constraints were clear, but not so outputs – eg, use of imprecise linguistic terms Decision:- Produce outputs to focus attention on areas of unusual activity (eg, abnormal shift in sales volume, market share, price) accompanied by associated factors to explain observation Problem domain not complex but universally (across all products, regions, seasons) applicable principles were difficult to identify Decision:- System to be flexible with parameterizable rules to suit specific circumstances Market data was of high quality ICT619 38 Case 1: An Expert System for Pattern Directed Data Mining (cont’d) Implementation The ES SPOTLIGHT was implemented using a rule based control engine written in C Sales database and rule base were 15 segments Loaded one segment at a time due to memory constraints Results of running each rule base on each segment of data integrated into final report Results Completed in 1991, SPOTLIGHT proved highly popular with sales reps and their clients Demonstrated feasibility of expert systems based on conventional technology - written in C for a PC platform, rather than in an AI language such as LISP for AI workstation First (?) successful data mining application of an expert system Case 1: An Expert System for Pattern Directed Data Mining (cont’d) Some limitations Gave limited analyses, and not interactive as a decision support tool Provided insight into what was happening in ...
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