The most serious problems standing in the way of developing an adequate theory of computation are as much ontological as they are semantical. It is not that the semantic problems go away; they remain as challenging as ever. It is just that they are joined – on center stage, as it were – by even more demanding problems of ontology.
– Smith [1996, p. 14]How do you represent knowledge about a world to make it easy to acquire, debug, maintain, communicate, share, and reason with that knowledge? This chapter explores how to specify the meaning of symbols in intelligent agents, how to use the meaning for knowledge-based debugging and explanation, and, finally, how an agent can represent its own reasoning and how this may be used to build knowledge-based systems. As Smith points out in the quote above, the problems of ontology are central for building intelligent computational agents.
Knowledge Sharing
Having an appropriate representation is only part of the story of building a knowledge-based agent. We also should ensure that the knowledge can be acquired from people and from data. The knowledge for any non-trivial domain comes from diverse sources and at multiple points in time. Multiple sources need to interoperate, to work together, at both a syntactic level and a semantic level.
Recall (page 67) that an ontology is a specification of the meanings of the symbols in an information system. Here an information system can be a knowledge base, a sensor such as a thermometer, or some other source of information. The meaning of the symbols is sometimes just in the mind of the knowledge base designer, in a user manual, or in comments with the knowledge base. Increasingly, the specification of the meaning is in machine-interpretable form. This formal specification of the meaning is important for semantic interoperability – the ability of different knowledge bases to work together at a semantic level so that the meanings of symbols are respected.
Example 14.1 A purchasing agent has to know, when a website claims it has a good price on “chips,” whether these are potato chips, computer chips, wood chips, or poker chips.
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