Abstract
The tools of artificial intelligence (AI) can be divided into two broad types: knowledge-based systems (KBSs) and computational intelligence (CI). KBSs use explicit representations of knowledge in the form of words and symbols. This explicit representation makes the knowledge more easily read and understood by a human than the numerically derived implicit models in computational intelligence. KBSs include techniques such as rule-based, modelbased, and case-based reasoning. They were among the first forms of investigation into AI and remain a major theme. Early research focused on specialist applications in areas such as chemistry, medicine, and computer hardware. These early successes generated great optimism in AI, but more broad-based representations of human intelligence have remained difficult to achieve (Hopgood, 2003; Hopgood, 2005).
TopBackground
The principal difference between a knowledge-based system and a conventional program lies in its structure. In a conventional program, domain knowledge is intimately intertwined with software for controlling the application of that knowledge. In a knowledge-based system, the two roles are explicitly separated. In the simplest case there are two modules: the knowledge module is called the knowledge base and the control module is called the inference engine. Some interface capabilities are also required for a practical system, as shown in Figure 1.
Figure 1. The main components of a knowledge-based system
Within the knowledge base, the programmer expresses information about the problem to be solved. Often this information is declarative, i.e. the programmer states some facts, rules, or relationships without having to be concerned with the detail of how and when that information should be applied. These latter details are determined by the inference engine, which uses the knowledge base as a conventional program uses a data file. A KBS is analogous to the human brain, whose control processes are approximately unchanging in their nature, like the inference engine, even though individual behavior is continually modified by new knowledge and experience, like updating the knowledge base.
As the knowledge is represented explicitly in the knowledge base, rather than implicitly within the structure of a program, it can be entered and updated with relative ease by domain experts who may not have any programming expertise. A knowledge engineer is someone who provides a bridge between the domain expertise and the computer implementation. The knowledge engineer may make use of meta-knowledge, i.e. knowledge about knowledge, to ensure an efficient implementation.
Traditional knowledge engineering is based on models of human concepts. However, it has recently been argued that animals and pre-linguistic children operate effectively in a complex world without necessarily using concepts. Moss (2007) has demonstrated that agents using non-conceptual reasoning can outperform stimulus–response agents in a grid-world test bed. These results may justify the building of non-conceptual models before moving on to conceptual ones.
TopTypes Of Knowledge-Based System
Expert Systems
Expert systems are a type of knowledge-based system designed to embody expertise in a particular specialized domain such as diagnosing faulty equipment (Yanga, 2005). An expert system is intended to act like a human expert who can be consulted on a range of problems within his or her domain of expertise. Typically, the user of an expert system will enter into a dialogue in which he or she describes the problem – such as the symptoms of a fault – and the expert system offers advice, suggestions, or recommendations. It is often proposed that an expert system must offer certain capabilities that mirror those of a human consultant. In particular, it is often stated that an expert system must be capable of justifying its current line of inquiry and explaining its reasoning in arriving at a conclusion. This functionality can be integrated into the inference engine (Figure 1).
Key Terms in this Chapter
Knowledge-Based System: System in which the knowledge base is explicitly separated from the inference engine that applies the knowledge.
Model-Based Reasoning: The knowledge base comprises a model of the problem area, constructed from component parts. The inference engine reasons about the real world by exploring behaviors of the model.
Forward Chaining: Rules are applied iteratively whenever their conditions are satisfied, subject to a selection mechanism known as conflict resolution when the conditions of multiple rules are satisfied.
Heuristic or Shallow Knowledge: Knowledge, usually in the form of a rule, that links evidence and conclusions in a limited domain. Heuristics are based on observation and experience, without an underlying derivation or understanding.
Closed-World Assumption: The assumption that all knowledge about a domain is contained in the knowledge base. Anything that is not true according to the knowledge base is assumed to be false.
Deep Knowledge: Fundamental knowledge with general applicability, such as the laws of physics, which can be used in conjunction with other deep knowledge to link evidence and conclusions.
Production Rule: A rule of the form if then .
Inference Network: The linkages between a set of conditions and conclusions.
Case-Based Reasoning: Solving new problems by adapting solutions that were previously used to solve old problem.
Backward Chaining: Rules are applied through depth-first search of the rule base to establish a goal. If a line of reasoning fails, the inference engine must backtrack and search a new branch of the search tree. This process is repeated until the goal is established or all branches have been explored.