Artificial Intelligence And Expert Systems For Engineers(16-30)

Artificial Intelligence and Expert Systems for Engineers by C.S. Krishnamoorthy; S. Rajeev CRC Press, CRC Press LLC ISBN: 0849391253 Pub Date: 08/01/96 Search Tips

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Chapter 2 Search Techniques

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2.1 Introduction Artificial Intelligence (AI) technology provides techniques for developing computer programs for carrying out a variety of tasks, simulating the intelligent way of problem solving by humans. The problems that humans solve in their day-to-day life are of a wide variety in different domains. Though the domains are different and also the methods, AI technology provides a set of formalisms to represent the problems and also the techniques for solving them. What AI technology provides us is what is described in the above sentences. Based on this, it is very difficult to precisely define the term artificial intelligence. Different people working in this topic for many years have proposed different definitions. According to Rich, AI is the study of how to make computers do things at which, at the moment, people are better [1]. It is observed that it is equally difficult to define human intelligence. Some of the essential activities associated with intelligence are listed in reference [1–2] and they are given below. a) To respond to situations flexibly b) To make sense out of ambiguous or contradictory messages c) To recognise the relative importance of different elements of a situation d) To find similarities between situations despite differences which may separate them e) To draw distinctions between situations despite similarities which may link them Simulation of the above activities in a computer is difficult. Also, most of the above actions are used by engineers in carrying out tasks such as planning, design, diagnosis, classification, monitoring etc. Hence, it is essential to look at them more closely in order to understand how they can be formally represented and used. Newell and Simon [3] proposed the physical symbol system hypothesis in 1972, which forms the heart of all the research and development work that takes place in the field of AI. It consists of a definition of a symbol structure and then a statement of the hypothesis, which is given below.

“A physical symbol system consists of a set of entities called symbols, which are physical patterns that can occur as components of another type of entity called an expression (or symbol structure). Thus, a symbol structure is composed of a number of instances or symbols related in some physical manner (such as one instance being next to another). At any instant of time the system will contain a collection of these symbol structures. Besides these structures, the system also contains a collection of processes that operate on expressions, creation, modification, reproduction and destruction. A physical symbol system is a machine that produces through time an evolving collection of symbol structures. Such a system exists in a world of objects wider than just these symbolic expressions themselves.” They then state the hypothesis as: A physical system has the necessary and sufficient means for general intelligent actions. The only way this hypothesis can be validated is by experimental and empirical means. Design solutions of engineering systems can be visualised as a symbol structure with collection of instances that are related to one another in some manner. Consider the case of a building system. It can be visualised as a collection of two subsystems, viz., a lateral load-resisting system and a gravity load-resisting system. These two systems are independent of each other and have no direct relationship with one another. But they are the successors of the system building. Hence they are related through the parent system. Each of these subsystems can further be visualised as a collection of subsystems. The lateral load-resisting system can be a reinforced concrete (RC) rigid frame, consisting of many beams and columns. The objects beam and column can have their own generic symbol structure with different attributes. Each of these can have many instances representing individual beams and columns, which are semantically related to the generic symbol beam or column. Engineering is a collection of a set of intelligent tasks, consisting of different activities such as planning, analysis, design, construction, management and maintenance. The five different manifestations of intelligence enumerated above are used at different stages of engineering of any system or artifact. Some typical instances in building engineering are presented below, in order to visualise the different situations that may arise requiring intelligent processing of information. a) To respond to situations flexibly During the planning stage of a building, the architect tries to generate the plan of a typical floor as a combination of different rooms or facilities. To begin with, only the area required for each facility, possibly the adjacency information among the facilities and the required orientation from the functional requirements are given. Any planning system first comes up with a plan, which may not fit into a proper shape and/or there may be voids in between. Now the system has to respond to this situation, which is going to be unique for different data sets, and generate decisions so that an acceptable plan is generated. This is a typical instance of an intelligent task, in which the system is expected to respond to situations flexibly. b) To recognise the relative importance of different elements of a situation There are many situations in a design process, where multiple solutions are generated, and it is required to select the best one from the alternatives. The system has to recognise the relative importance of the different solutions and then make a selection. Consider the following situation. Basic heuristics states that: IF THEN IF THEN

number of stories < 15 provide RC rigid frame for lateral load resistance number of stories > 20 provide shear wall also along with RC rigid frame for lateral load resistance.

Now if the number of stories is between 15 and 20, other factors are also to be considered, such as wind zone, type of live load that is going to come on the floors, spacing of columns in the RC rigid frame etc., to decide whether shear wall is to be provided or not. The system has to recognise the relative importance of different scenarios and take an appropriate decision. c) To find similarities between situations despite differences which may separate them

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