Chapter 6 - Expert Systems and Knowledge Acquisition
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Universiity of Pretoria etd – De Kock, E (2003) Chapter 6 - Expert Systems and knowledge acquisition An expert system’s major objective is to provide expert advice and knowledge in specialised situations (Turban 1995). ES is a sub-discipline of AI (Turban et al 2001). For an ES to reason, provide explanations and give advice, it needs to process and store knowledge. Knowledge in the form of facts and rules are kept in a knowledge base. 6.1 Expert System definitions ES definitions by Turban et al (2001) and Olson & Courtney (1992) were presented in Paragraph 2.3.1 (p19). Raggad & Gargano (1999) state: “ES emerged, as a branch of AI, from the effort of AI researchers to develop computer programs that could reason as humans”. Goodall (1985) distinguishes two approaches when defining an expert system: • The human/AI oriented approach, and • The technology oriented approach Goodall’s (1985) AI approach defines an expert system as a computer system that performs functions similar to those normally performed by a human expert. He extends this definition to include the nature of an expert system, in other words, he includes how ES behaves, in the technology approach: “An expert system is a computer system that uses a representation of human expertise in a specialist domain in order to perform functions similar to those normally performed by a human expert in that domain”. In formulating the above definition, Goodall (1985) focused on the implementation of two types of ES: • ES performing at a suitable ‘high’ expert level, and • ES that performs tasks which no human expert has, using perhaps a very complex set of rules to control a chemical process at a speed and in circumstances (e.g. temperature, time, location) which no human could possibly match. Such a system will most surely outperform the best human expert. The value of ES as a sub-discipline of AI (Turban et al 2001), can be appreciated more when comparing AI to natural intelligence and conventional programs. Kaplan (1984) as referred to by Turban et al (2001), states several commercial advantages of AI over natural intelligence: • AI is more permanent. Employees take knowledge with them when they leave their place of employment, or worse: an employee may even forget his knowledge. As long as the computer systems and programs remain unchanged, the knowledge remains the same. 107 Universiity of Pretoria etd – De Kock, E (2003) • AI offers ease of duplication and dissemination. Transferring knowledge between persons may be a lengthy process. Some expertise is never transferred. Knowledge embodied in a computer system can be easily moved to another computer. • AI can be less expensive than natural intelligence. Buying computer services can cost less than having a human performing the same task. • AI is a computer technology and thus consistent and thorough. Natural intelligence is erratic because people are erratic and perform inconsistently. , and • AI can be documented. Decisions made by a computer can easily be documented by tracing the activities of the system. Natural intelligence is difficult to document. A conclusion reached may be difficult to be recreated or recalled later. Some of the assumptions or even the reasoning process may be forgotten. Natural intelligence has several advantages over AI: • Natural intelligence is creative: In an AI system, knowledge has to be carefully constructed, while knowledge is inherent to all human beings • Natural intelligence uses sensory experienced directly: Users using AI, use sensory experiences indirectly • Natural intelligence enables people to recognise relationships between artefacts, sense qualities and spot patterns that explain how various items interrelate, and • A wide context of experiences is used when natural intelligence solves an individual problem, while AI typically gains its power by having a very narrow focus ES differs from conventional programs too. Raggad & Gargano (1999) and Turban et al (2001) summarise the characteristics of conventional programs as follows: • Conventional Computer Based Information Systems (CBIS) processes data and information as a direct conceptual resource • Conventional programs are based on algorithms or mathematical formulas and sequential procedures that lead to a solution using data to solve problems • The objective of CBIS is to create and efficient solution by designing an efficient algorithm • CBIS are characterised by repetitive processing • The processing system or control mechanism of the system and the knowledge of the subject are intertwined as part of the sequence of instructions • Knowledge of the subject is built into the processing mechanism or control of the system. The subject knowledge or business rules form part of the sequence of instructions. All business rules are part of the program code. The knowledge is stored as control embedded in the program instructions. The control is the sequence in which the transactions are performed. The programmer fixes these steps in advance. It is called the algorithm of the program. • To change the business rules or domain knowledge a programmer needs to edit the program and insert or change the statements that represent the information in the correct place 108 Universiity of Pretoria etd – De Kock, E (2003) • The program or system used does not explain which rules were used during processing of data to produce the output • The program is specialised to deal with specific information. A complete system of programs and input are necessary to achieve something useful. • One missing essential step causes the program(s) to malfunction. The data that are processed should be complete and certain to achieve an appropriate result or valid output. • Error detection of the domain knowledge is performed when executing the program and noticing faulty output • CBIS frequently uses algorithms in its search approach ,and • CBIS has no reasoning capability except for a fixed process in the algorithm of the program, and • Updating and maintenance of data and information are usually difficult When with conventional programs, the characteristics of ES are: • The main conceptual source of ES is knowledge. ES can expand to include a knowledge acquisition component that processes data and information into rules. Data and information are indirect conceptual resources. • ES does not represent its knowledge in algorithmic-like procedures. AI is based on symbolic processing of knowledge. Knowledge is represented by symbols such as letters, words or numbers that represent objects, processes and their relationships. The knowledge base contains facts and concepts and relationships among them. Processes are used to manipulate the symbols in the knowledge base to generate advice or recommendations to solve problems. • The objective of ES is to create an efficient knowledge representation to support the inference mechanism • ES keeps the control separate from the rules: the inference engine is responsible for most of the control. The knowledge base contains the rules or knowledge. • Knowledge is expressed as data and not encoded in the control of the ES. This has the advantage that knowledge can be returned to the user as explanations of the ES conclusions. • The order of the rules in the knowledge base does not matter • ES provides an explanation facility • The rules that comprise the knowledge may be built bit-by-bit, a rule at a time. ES can tolerate imperfect, incomplete or uncertain business rules or domain knowledge. • The ES will produce results even if the knowledge base is incomplete and uncertain. This is because of the separation of the knowledge and control components. • ES frequently uses heuristics in its search approach • ES has a reasoning capability, and • Maintenance and updating of data are relatively easy. Changes can be made in self-contained modules. 109 Universiity of Pretoria etd – De Kock, E (2003) 6.1.1 When to use an Expert System ES is appropriate for a limited number of problem domains. The task should be well bounded and should not include a large number of event combinations. A general rule of thumb is that if the average employee can solve the problem in a few minutes it is not worth solving it by an expert system. ES is appropriate (Raggad & Gargano 1999; Mallach 1994): • If great costs are involved when making the decision • When applied to repetitive problem domains, the task must be performed often • When a big difference exists between the best solution and the worst solution • When test data is easy available to test and validate the ES • When there is a general agreement on the system’s conclusions. Errors in the input should be tolerated in the system output. Experts must agree on the solutions. • When recognised expertise is available and a necessity during the development of the ES • If the problem is clearly specifiable in the area of expertise i.e. what the system is supposed to do before it is done, the desired system can be developed • If the problem is identifiable with a human expert, that is based on human expertise. Experts must perform the task substantially better than non-experts. The human expertise must be scarce. • If the problem domain is well bounded: for example defining criteria to determine the subject matter within the system from the matter outside of the system: The task is reasonably stable and within an acceptable narrow domain. • If solving the problem is based on knowledge rather than common sense reasoning: ES is based on knowledge and naïve systems on reasoning. • The solution has to be possible, justifiable and concisely generated (using only a few hundred rules), and • The knowledge has to be of a cognitive style and independent of common sense. Physical activities are ruled out. Goodall (1985) provides a comprehensive list of suitable types of tasks appropriate using ES in solving problems that includes: • Interpretation • Prediction • Diagnosis • Debugging • Design • Planning • Monitoring • Instruction, and • Control 110 Universiity of Pretoria etd – De Kock, E (2003) Turban et al (2001) calls the above-mentioned types the generic categories of Expert Systems.