Knowledge Base Systems production rule representation

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    19-Dec-2015

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  • Slide 1
  • Knowledge Base Systems production rule representation.
  • Slide 2
  • Production Systems Introduction These are a form of knowledge representation which have found widespread application in AI particularly in the area of Expert Systems. Production systems consist of three parts: a) A rule base consisting of a set of production rules. b) the data c) an interpreter which controls the systems activity.
  • Slide 3
  • Production Rules A production rule can be thought of as a condition action pair. They take the form IF condition holds THEN do action e.g. IF traffic light is red THEN stop car.
  • Slide 4
  • Firing Production Rules A production rule whose conditions are satisfied can fire, i.e. the associated actions can be performed. Conditions are satisfied or not according to what data is currently available. Existing data may be modified as production rules are fired. Changes in data can lead to new conditions being satisfied. New production rules may then be fired.
  • Slide 5
  • The decision which production rule to fire next is taken by a program known as the interpreter. The interpreter therefore controls the systems decisions and actions and must know how to do this.
  • Slide 6
  • Production Systems Production systems were first proposed in 1943 by Post. Present day systems however bear little resemblance to those earlier ones. Newell and Simon in 1972 used the idea of production systems for their models of human cognition and AI in general has found widespread use for them.
  • Slide 7
  • Suitable Domains Davis and King (1977) proposed the following criteria for problem domains where productions rules are suitable. 1: Domains in which knowledge is diffuse, consisting of many different strands of knowledge rather than some domain which is based on a unified theory like Physics. 2: Domains in which processes cane be represented as a set of independent actions as opposed to domains with dependent subprocesses. 3: Domains in which knowledge can be easily separated from the manner in which it is to be used as opposed to cases where representation and control are merged.
  • Slide 8
  • Knowledge Base Systems Knowledge Base systems are intended to perform tasks which require some specialized knowledge and reasoning. Medical diagnosis, geological analysis, and chemical compound identification are examples of tasks to which Knowledge Base systems have been applied.
  • Slide 9
  • Expert Systems Knowledge Base systems are often called expert systems because the problems in their application domain are usually solved by human experts. For example medical diagnosis is usually performed by a doctor.
  • Slide 10
  • Parts of a Knowledge Base System Knowledge Base systems consist of Four major parts; The Knowledge Base, The Inference Engine The User Interface and The Explainer Knowledge Acquisition Module
  • Slide 11
  • Inference Engine Agenda Knowledge Base (rules) Explanation Facility User Interface Knowledge Acquisition Facility Working Memory (facts)
  • Slide 12
  • The knowledge to which the Knowledge Base system has access, is stored in the Knowledge Base, (hence the name). The Inference Engine is the part of a Knowledge Base system which is responsible for using its knowledge in a productive way. The Knowledge Base system's reasoning mechanisms are built into the Inference Engine. Most Knowledge Base systems employ deductive reasoning mechanisms.
  • Slide 13
  • The Knowledge Base system communicates with the user through the User Interface. In many applications the Knowledge Base system is required to explain its reasoning to the user. This is particularly true in situations such as the identification of chemical structures where new results must be verified. The Explainer is that part of the Expert System which provides explanation and verification
  • Slide 14
  • Knowledge Acquisition Modules These help with acquiring the systems knowledge. They do a variety of tasks for example in some systems they provide system analysis facilities similar to those of database development tools Mostly they help encode the knowledge from a high level format into a computer usable representation.
  • Slide 15
  • System Architecture
  • Slide 16
  • Inference Engine Agenda Knowledge Base (rules) Explanation Facility User Interface Knowledge Acquisition Facility Working Memory (facts)
  • Slide 17
  • Obviously the knowledge to which a Knowledge Base system has access is no good to it, if it cannot use it to solve the problems in the application domain. Therefore the systems knowledge must be represented in a form which can be manipulated by the reasoning mechanisms of the Inference Engine.
  • Slide 18
  • While the Knowledge Base, the IE and the User Interface are essential components, in many Knowledge Base systems there are also facilities to help in the acquisition of new knowledge. Teiresias, [DAVIS '76], which is used in association with MYCIN, [Shortliffe '76, Davis '76] is an example of such a system. It elicits high level information from the user which it converts into structured knowledge for its Knowledge Base. It also performs consistency checks on the updated knowledge base. The ability to acquire new knowledge is important since the amount of knowledge to which a system has access determines the range of problems which it can solve.
  • Slide 19
  • Applications of Knowledge Base systems Knowledge Base systems have been applied to many diverse problem domains, such as the following. Diagnostic Aids such as MYCIN, [Shortliffe '76, Davis '76], which diagnoses bacterial blood infections and PUFF, [Kunz et al '78], which diagnose pulmonary disorders. MYCIN was a joint venture between Dept. of Computer Science and the Medical School of Stanford University. Much of the work took place in the 1970's. Mycin was designed to solve the problem of diagnosing and recommending treatments for meningitis and bacteremia, (blood infections).
  • Slide 20
  • Aids to Design and Manufacture such as R1, [McDermott '82], which configures computers. Teaching Aids such as SCHOLAR [Carbonell '70] which gives Geography Tutorials and SOPHIE, [Brown et al '82], which teaches how to detect breakdown in electrical circuits. Problem Solving
  • Slide 21
  • Recognition of forms, e.g. DENDRAL, [Buchanan and Feigenbaum '78, Lindsay et al '80], which recognizes the structures of chemical compounds. Robotics e.g. SHDRLU, [Winograd '73], which manipulates polygons in a restricted environment. Game playing systems such as Waterman's Poker Player, [Waterman '70], and
  • Slide 22
  • Automatic theorem Provers such as AM, [Lenat '82]. [Hayes-Roth et al '83, Handbook A.I. '82, Waterman '86], describe some more categories than those mentioned above. These include Planning systems such as NOAH, [Sacerdoti '75] and MOLGEN, [Friedland '75] and Prediction systems such as Political Forecasting Systems, [Schrodt '86] based on the Holland Classifier, [Holland '86].
  • Slide 23
  • Rule-Based Expert Systems Work with a set of facts describing the current world state a set of rules describing the expert knowledge inference mechanisms for combining facts and rules in reasoning
  • Slide 24
  • Architecture of Rule-Based XPS 1 Knowledge-Base / Rule-Base stores expert knowledge as condition-action- rules (or: if-then- or premise-consequence-rules) objects or frame structures are often used to represent concepts in the domain of expertise, e.g. club in the golf domain. Working Memory stores initial facts and generated facts derived by the inference engine additional parameters like the degree of trust in the truth of a fact or a rule ( certainty factors) or probabilistic measurements can be added
  • Slide 25
  • Knowledge Engineering Knowledge engineering is a general term for the processes involved in building expert systems: planning, knowledge acquisition, system building,system installation, system maintenance. In the following notes "KE" stands for knowledge engineer, and "DE" stands for domain expert.
  • Slide 26
  • Architecture of Rule-Based Systems Inference Engine matches condition-part of rules against facts stored in Working Memory (pattern matching); rules with satisfied condition are active rules and are placed on the agenda; among the active rules on the agenda, one is selected (see conflict resolution, priorities of rules) as next rule for execution (firing) consequence of rule can add new facts to Working Memory, modify facts, retract facts, and more
  • Slide 27
  • Rule-Based Systems - Example Grades - Rules to determine grade 1.If study then get good_grade 2.If do not_study then get bad_grade 3.If sun_shines THEN go_out 4.If go_out then do not_study 5.If stay_home then study 6.If awful_weather then stay_home
  • Slide 28
  • Questions Ask the following questions of the expert System Q1: If the weather is awful, do you get a good or bad grade? Q2: When do you get a good grade?
  • Slide 29
  • forward reasoningrule chain given fact: awful_weather 6,5,1 backward reasoning hypothesis/goal: good_grade 1,5,6 Answer Question 1 Good Grade Exercise Answer question 2 with forward and backward chaining
  • Slide 30
  • Explaini

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