DOC PREVIEW
LEHIGH CSE 335 - Expert Systems

This preview shows page 1-2-3-4-27-28-29-30-55-56-57-58 out of 58 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 58 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Expert SystemsPresented by Ulit JaideeWhat is an expert system?• An expert system uses knowledge specific to a problem domain to provide “expert quality” to perform in a specific application area• An expert system is an interactive computer-based decision tool that uses both facts and rules to solve difficult decision problems based on knowledge acquired from an expert.Applications of Expert SystemsMYCINMedical system for diagnosing blood disorders. First used in 1979DENDRAL: Used to identify the structure of chemical compounds. First used in 1965Applications of Expert SystemsPROSPECTOR:Used by geologists to identify sites for drilling or mining. First used in 1978 (found a $100M ore deposit)XCONConfigure VAX and PDP-11 series.First used in 1984(saved DEC $70M per year)Applications of Expert SystemsLITHIAN: Gives advice to archaeologists examining stone toolsPUFF:Medical system for diagnosis of respiratory conditions. Fist used in 1979Categories of Expert SystemsMost applications of expert systems will fall into one of the following categories:• Interpreting and identifying• Predicting• Diagnosing• Designing• Planning• Monitoring• Debugging and testing• Instructing and training• ControllingWhy use Expert Systems?Human experts are not always available. An expert system can be used anywhere, any time.Human experts are not 100% reliable or consistentHuman experts may not be good at explaining decisionsCost effectiveProblems with Expert SystemsLimited domainSystems are not always up to date, and do not learnNo “common sense”Experts (or engineers) needed to setup and maintain systemCommon characteristics• System performs at a level generally recognized as equivalent to a human expert in the field• System is highly domain specific• System can explain its reasoningSystem Architecture•Usually expert systems are rule-based—Extract expert knowledge in the form of rules & facts(Domain-specific)KNOWLEDGEBASEUSERINTERFACEINFERENCE ENGINECASE-SPECIFICDATAUserExpert SystemSystem Architecture (cont’)• The knowledge base is the collection of facts and rules which describe all the knowledge about the problem domain• The inference engine is the part of the system that chooses which facts and rules to apply when trying to solve the user’s query• The user interface is the part of the system which takes in the user’s query in a readable form and passes it to the inference engine. It then displays the results to the user.• The case-specific data is working memoryDevelopment ProcessKnowledge Representation• Traditionally the most popular form of knowledge representation in expert systems is production rules.• Examples of rules:– if condition P then conclusion C– if situation S then action A– if conditions C1and C2hold then conclusion C does not holdInference example• Consider the following rules about diagnosing auto problemsRule#ConditionConsequenceR1If gas_in_engine and turns_overThen problem(spark_plugs)R2If not (turns_over) and not(lights_on)Then problem(battery)R3If not(turns_over) and lights_onThen problem(starter)R4If gas_in_tank and gas_in_carbThen gas_in_engineUSERINTERFACECASE-SPECIFICDATAKNOWLEDGEBASEINFERENCE ENGINEInference example (cont’)R1R2R3R4Example rule from MYCINif1 the infection is primary bacteremia, and2 the site of the culture is one of the sterilesites, and3 the suspected portal of entry of the organism is the gastrointestinal tractthenthere is suggestive evidence (0.7) that the identity of the organism is bacteroides.Example rules from AL/X• Diagnosing equipment failure on oil platforms, Reiter 1980ifthe pressure in V-01 reached relief valve lift pressurethenthe relief valve on V-01 has lifted [N = 0.005, S = 400]ifNOT the pressure in V-01 reached relief valve lift pressure,and the relief valve on V-01 has liftedthenthe V-01 relief valve opened early (the set pressure has drifted)[N = 0.001, S = 2000]Example rule from AL3game playing, bratko 1982if1 there is a hypothesis, H, that a plan P succeeds, and2 there are two hypotheses,H1, that a plan R1 refutes plan P, andH2, that a plan R2 refutes plan P, and3 there are facts: H1 is false, and H2 is falsethen1 generate the hypothesis, H3, that the combined plan ‘R1 or R2' refutes plan P, and2 generate the fact: H3 implies not(H)Inference MethodsForward vs. Backward chaining Forward chaining or Data driven reasoning –an inference technique which uses IF THEN rules to deduce a problem solution from initial data Backward chaining or Goal driven reasoning –an inference technique which uses IF THEN rules to repetitively break a goal into smaller sub-goals which are easier to proveForward chaining• Idea: fire any rule whose premises are satisfied in the KB,– add its conclusion to the KB, until query is foundBFAFLBARLPARMLBRPMLRQPR:::::::2154321Backward chainingIdea: work backwards from the query q• check if q is known already, or• prove by BC all premises of some rule concluding q• Hence BC maintains a stack of sub-goals that need to be proved to get to q.Avoid loops: check if new sub-goal is already on the goal stackAvoid repeated work: check if new sub-goal1. has already been proved true, or2. has already failedBackward chaining exampleBackward chaining exampleBackward chaining exampleBackward chaining examplewe need P to proveL and L to prove P.Backward chaining exampleBackward chaining exampleBackward chaining exampleBackward chaining exampleBackward chaining exampleBackward chaining exampleDemo: FC vs. BC •FORWARD CHAINING•BACKWARD CHAININGForward vs. backward chaining• Forward chaining is data-driven, automatic, unconscious processing,– e.g., object recognition, routine decisions• May do lots of work that is irrelevant to the goal • Backward chaining is goal-driven, appropriate for problem-solving,– e.g., Where are my keys? How do I get into Windows Device Manager?• Complexity of Backward chaining can be much less than linear in size of Knowledge BaseFC & BC in First-Order LogicAn Example: The law says that it is a crime for an American to sell weapons to hostile nations. The country Nono, an enemy of America, has some missiles, and all of its missiles were sold to it by Colonel West, who is American.• ... it is a crime for an American to sell weapons to hostile nations:American(x) Weapon(y) Sells(x,y,z) Hostile(z) Criminal(x)• Nono … has


View Full Document

LEHIGH CSE 335 - Expert Systems

Download Expert Systems
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Expert Systems and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Expert Systems 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?