Automobile Diagnosis Expert System
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This document describes the steps involved in designing an expert system for automobile diagnosis using a forward chaining rule-based approach. It outlines defining the problem of hard starting, input data like start-up rules, and a data-driven structure. An initial set of rules is written to test the cranking, ignition, and fuel systems. The knowledge base and working memory are populated with sample rules and facts. Finally, designing the user interface in parallel is discussed.
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Automobile Diagnosis Expert System
- 1. Lecture 25
- 2. Case Study: Designing Rule-based Expert Systems Automobile Diagnosis Expert System
- 3. Introduction • Consider a small problem in automobile diagnosis. • Review the step involved in this task as an example of typical course taken when developing forward chaining rule based systems.
- 4. Steps • Define the problem • Define the input data • Define the structure (data driven) • Write initial code • Test • Design the interface • Expand the system • Evaluate the system
- 5. Automobile Diagnosis • Attractive area – Useful – Rules readily available • Typically diagnostic systems are based on backward chaining. • Since there can be a number of problems leading to a large set of facts hence it may be advisable to use FWD chaining • Inherently data driven approach to solving automobile diagnosis problem, therefore more natural to use forward chaining.
- 6. Task 1: Define the Problem • Learn about automobile diagnostics. Possible sources of information – A good car mechanic – A trouble-shooting manual • Auto-repair manuals – Series of tests to identify problem. – Decision trees – Checklist type tests – Sections grouped by principal problems – Narrowing down problems: subsystems • Problem to diagnose is hard starting
- 7. Subsystems • Cranking System • Ignition System • Fuel System • Engine Compression System
- 8. Decision tree Durkin Fig 10.1 Engine does not start Cranking system good Ignition system good Fuel system good Cranking system bad Ignition system bad Fuel system bad Test Cranking system Test Ignition system Test Fuel system Test Compression system
- 9. 1 - Problem Specifications • Scope – ‘Engine does not start’ problems – Address only cranking problems
- 10. 2 - Define Input Data • Start-up Rule (auto fire on start up) Rule 1: Start IF Task is Start THEN Ask what is the problem?
- 11. 3 - Define Structure • Data driven structure • Incorporate flow control into the premises of rules, e.g. IF Task is test engine --- Type of test AND Lights are dim --- Result THEN test battery --- Proceed to
- 12. 4 - Write initial code • Subset of rules that capture the general structure. • Purpose: To verify that we have effectively captured the problems knowledge in our rule structure. • A good structure is one that not only provides correct results but also a template to follow for the development of other rules
- 13. Knowledge Base Rule 1: IF Task is start THEN Ask problem Rule 2: IF problem is car does not start THEN Task is to test cranking system Rule 3: IF problem is car gives problem at high speeds THEN Task is test fuel system Working Memory Task is start What is the problem? -car does not start -car gives problem at at high speeds
- 14. Knowledge Base Rule 1: IF Task is start THEN Ask problem Rule 2: IF problem is car does not start THEN Task is to test cranking system Rule 3: IF problem is car gives problem at high speeds THEN Task is test fuel system Working Memory Task is start Problem is car does not start
- 15. Knowledge Base Rule 1: IF Task is start THEN Ask problem Rule 2: IF problem is car does not start THEN Task is to test cranking system Rule 3: IF problem is car gives problem at high speeds THEN Task is test fuel system Working Memory Problem is car does not start Task is to test cranking system
- 16. Knowledge Base Rule 4: IF Task is to test cranking system THEN Ask how engine turns Rule 5: IF Task is to test cranking system AND engine turns slowly/doesn’t turn THEN Cranking system is not working AND Task is to test battery connection Rule 6: IF Task is to test cranking system AND Engine turns normally THEN Cranking system is working AND Task is to test ignition system Working Memory Problem is car does not start Task is to test cranking system How does the engine turn upon ignition? -slowly/doesn't turn -normally
- 17. Knowledge Base Rule 4: IF Task is to test cranking system THEN Ask how engine turns Rule 5: IF Task is to test cranking system AND engine turns slowly/doesn’t turn THEN Cranking system is not working AND Task is to test battery connection Rule 6: IF Task is to test cranking system AND Engine turns normally THEN Cranking system is working AND Task is to test ignition system Working Memory Problem is car does not start Task is to test cranking system Engine turns slowly/doesn’t turn
- 18. Knowledge Base Rule 7: IF Task is to test battery connection THEN Ask about Screwdriver test Rule 8: IF Task is to test battery connection AND Screwdriver test shows that lights brighten OR Screwdriver test shows that lights do not turn on THEN Problem is a bad battery connection Rule 9: IF Task is to test battery connection AND Screwdriver test shows that lights don’t brighten THEN Battery connection is good AND Task is test battery Working Memory Problem is car does not start Engine turns slowly/doesn’t turn •Cranking system is not working •Task is to test battery connection Do screwdriver test. What happens to the lights? -brighten -not on -don’t brighten
- 19. Knowledge Base Rule 7: IF Task is to test battery connection THEN Ask about Screwdriver test Rule 8: IF Task is to test battery connection AND Screwdriver test shows that lights brighten OR Screwdriver test shows that lights do not turn on THEN Problem is a bad battery connection Rule 9: IF Task is to test battery connection AND Screwdriver test shows that lights don’t brighten THEN Battery connection is good AND Task is test battery Working Memory Problem is car does not start Engine turns slowly/doesn’t turn •Cranking system is not working •Task is to test battery connection •Screwdriver test shows that lights brighten
- 20. Knowledge Base Rule 7: IF Task is to test battery connection THEN Ask about Screwdriver test Rule 8: IF Task is to test battery connection AND Screwdriver test shows that lights brighten OR Screwdriver test shows that lights do not turn on THEN Problem is a bad battery connection Rule 9: IF Task is to test battery connection AND Screwdriver test shows that lights don’t brighten THEN Battery connection is good AND Task is test battery Working Memory Problem is car does not start Engine turns slowly/doesn’t turn •Cranking system is not working •Task is to test battery connection •Screwdriver test shows that lights brighten •Problem is a bad battery connection
- 21. Design the Interface • Begin design of interfaces in parallel with development of rules • Interfaces interactive • Graphical user interface • Display screens – Introduction screen – Intermediate findings screen – Conclusions • Question screens
Editor's Notes
- 1)Obtain a general understanding of the problem define the project objective major problem issues how experts deal with the information to reach a recommendation 2)Remember that unlike backward chaining systems that start with a goal and then works back through the rules to prove the goal, forward chaining systems work with the given information and rules to generate new information. 3)In backward chaining the inference engine directs the control from the goal to sub-goals. You as a programmer just write the rules and expect the inference engine to work out the strategy for using the rules to prove any given goal. This is not true for forward chaining rule based systems, where you have to explicitly lay down the control, since on its own the inference engine will simply match fire rules whose premises match the given information. You cannot allow this to happen in an unconstrained manner. As we will see in the course of this case study, we have to lay down a control strategy. 4)Designing an expert system is an ITERATIVE process. You start with a small set of rules, test them, and then incrementally add new knowledge to the system.
- Typically diagnostic problems are based on backward chaining, because intuitively you set the fault as your goal and ask the system to work with it. But when the number of possible faults grows large this is harder to do. E.g in the automobile diagnostic system, there may be hundreds of possible faults, you cannot make that many goal rules. It would be impractical. Instead an expert starts with some important information, then gathers other important clues along the course of the investigation to come up with a diagnosis. This style of problem solving is inherently data driven and best managed with a forward chaining rule based system.
- Manuals: For most diagnosis problems, e.g automobile, plumbing, clock repair, manuals exist that can aid in trouble shooting. They are developed by the relevant industry to aid technicians to carry out these tasks in a step-by-step methodical manner. Ease of availability and ease of use are two attributes a manual must have to be useful to us. Auto-repair manuals fortunately are readily available.
- Decision tree for ‘engine does not start problems’ Notice that this process is heuristic in nature. The order in which the various systems are tested follows a path that is heuristically most likely to find the fault. Durkin Fig10.1
- Every forward chaining rule based system needs to first obtain some initial data to get started. Therefore, we need to write a rule whose only task is to get some information about the problem. This type of rule is called a start-up rule and fires automatically upon starting the system. When it fires it asks a question. For our system we want it to ask the user about the general nature of the problem. Q) What is the problem; Car wont start, car hesitates at high speeds. After the user answers the initial question the systems directs the problems solving process. To keep our system simple, we will only ask to cater to the problems ‘car wont start’. Then the system interactively asks the user to answer questions to guide the system through to a logical conclusion
- In addition to lights don’t brighten, we add a premise that controls the firing of the rule (only when the engine is being tested, will this rule fire)
- Test our small set of rules. Lets dry run our set of rules to test our structure.
- Test our small set of rules. Lets dry run our set of rules to test our structure.
- Test our small set of rules. Lets dry run our set of rules to test our structure.
- Test our small set of rules. Lets dry run our set of rules to test our structure.
- Test our small set of rules. Lets dry run our set of rules to test our structure.
- Test our small set of rules. Lets dry run our set of rules to test our structure.
- Test our small set of rules. Lets dry run our set of rules to test our structure.
- Test our small set of rules. Lets dry run our set of rules to test our structure.