(19th-July-2020)
• A simple form of a knowledge base that is told facts about what is true in the world. An agent can use such a knowledge base, together with its observations, to determine what else must be true in the world. When an agent is queried about what is true given a knowledge base, it can answer the query without enumerating the possible worlds, or even generating any possible worlds.
• This chapter presents a number of reasoning formalisms that use propositions. They differ in what is being proved, what background knowledge must be provided, and how the observations that the agent receives online are handled.
• Writing constraints extensionally as tables of legal values for variables is not very intuitive. It is difficult to see what the tables are saying. It is also difficult to debug the knowledge, and small changes in the problem can mean big changes to the tables. One way to write constraints intensionally is in terms of propositions.
• There are a number of reasons for using propositions for specifying constraints and queries:
• It is often more concise and readable to give a logical statement about the relationship between some variables than to use an extensional representation.
• The kind of queries an agent may have to answer may be richer than single assignments of values to variables.
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