Production System

Production System

CONTENTS • Introduction • Components of production system • Production Rules • Data Base • Control program • Working of production system • Control of search in production system • Data driven search • goal driven search • Advantages • Limitations

Introduction • The production system is a model of computation that has proved particularly important in Artificial intelligence, both for implementing search algorithms and for modeling human problem solving. • A production system provides pattern directed control of a problem-solving process and consists of a set of production rules, a working memory and a recognize-act control cycle. • A production system provides the mechanism necessary to execute productions in order to achieve some goal for the system. BACK

Components of production system • A production system is defined by three components: Components of production system Control Program Production Rules Data Base BACK

Production Rules • These are often simply called productions. • A production is a condition action pair and defines a single chunk of problem-solving knowledge. • A rule or production is a statement that has two parts: (a) antecedent i.e. condition also known as premise (b) consequent i.e. action also known as conclusion • The condition part of the rule is a pattern that determines when that rule may be applied to a problem instance. The action part defines the associated problem-solving step. • For Exp:- IF patient has high fever and body ache THEN disease is flu. In the above production rule antecedent is “patient has high fever and body ache” and consequent is “disease is flu”. BACK

Data Base • This is also known as working memory. • It contains a description of the current state of the world in a reasoning process. • This description is a pattern that is matched against the condition part of a production to select appropriate problem-solving actions. • When the condition element of a rule is matched by the contents of working memory, the action associated with that condition may then be performed. • The actions of production rules are specifically designed to alter the contents of working memory. BACK

Control program • This is also known as recognize-act cycle. • The control structure for a production system is straightforward. • Working memory is initialized with the beginning problem description. • The pattern in working memory are matched against the conditions of the production rules; this produces a subset of the productions called conflict set, whose conditions match the pattern in working memory. • The production in the conflict set are said to be enabled. • One of the production in the conflict set is then selected and the production is fired.

Cont…. • That is, the action of the rule is performed, changing the contents of working memory. • After the selected production rule is fired, the control cycle repeats with the modified working memory. • The process terminates when no rule conditions are matched by the contents of working memory. BACK

Working of production system The working of a production system can be explained using the following algorithm: 1. DATA initial database 2. Until DATA satisfies termination condition do: 3. begin: Match the rules in R with DATA to find the applicable rules. If more than one rule are applicable to DATA then resolve the conflict and select some rule, R. DATA result of applying R to DATA.

Cont…. Following figure shows the working process of production system. This process is carried out recursively in three stages:- Knowledge Base Match Conflict Set Select Execute Working Memory Working of production System BACK

Control of search in production system There are two strategies for controlling the search in production system. • Data driven search • Goal driven search

Data driven search • Data-driven search begins with a problem description and infers new knowledge from the data, • This is done by applying rules of inference, legal moves in a game, or other state-generating operations to the current description of the world and adding the results to that problem description. • This process continues until a goal is reached.

Cont….. For Exp:- Production set: 1. p & q goal 2. r & s p 3. w & r q 4. t & u q 5. v s 6. start v & r & q BACK Data Driven Search

Goal Driven Search • The goal-driven search begins with a goal and works backward to establish its truth. • To implement this in a production system, the goal is placed in working memory and matched against the ACTIONs of the production rules. • These ACTIONs are matched just as the CONDITIONs of the productions were matched in the data-driven reasoning. • All production rules whose ACTIONs match the goal form the conflict set. • When the ACTION of a rule is matched, the CONDITIONs are added to working memory and become the new sub goals of the search. • The process continues until a start is reached.

Cont….. For Exp:- Production set: 1. p & q goal 2. r & s p 3. w & r q 4. t & u q 5. v s 6. start v & r & q Goal Driven Search BACK

Advantages The major advantages of production systems for artificial intelligence include: • Explanation • Modification • Understanding • Modularity of Production Rules • Pattern-Directed Control • Separation of knowledge and control • Language Independence BACK

Limitations • In spite of these advantages, production rules do have the following shortcomings: • Production rules lack expressive power for description of situations. • When the number of rules is large, it becomes difficult to check whether or not a new rule brought into the system is redundant or in conflict with the existing ones. • Production rules have a fixed format. BACK

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Production System