# chapter03 - Chapter 3 Methods of Inference Expert Systems...

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Chapter 3: Methods of Inference Expert Systems: Principles and Programming, Fourth Edition

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Expert Systems: Principles and Programming, Fourth Edition 2 Objectives Learn the definitions of trees, lattices, and graphs Learn about state and problem spaces Learn about AND-OR trees and goals Explore different methods and rules of inference Learn the characteristics of first-order predicate logic and logic systems
Expert Systems: Principles and Programming, Fourth Edition 3 Objectives Discuss the resolution rule of inference, resolution systems, and deduction Compare shallow and causal reasoning How to apply resolution to first-order predicate logic Learn the meaning of forward and backward chaining

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Expert Systems: Principles and Programming, Fourth Edition 4 Objectives Explore additional methods of inference Learn the meaning of Metaknowledge Explore the Markov decision process
Expert Systems: Principles and Programming, Fourth Edition 5 Trees A tree is a hierarchical data structure consisting of: Nodes – store information Branches – connect the nodes The top node is the root, occupying the highest hierarchy. The leaves are at the bottom, occupying the lowest hierarcy.

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Expert Systems: Principles and Programming, Fourth Edition 6 Trees Every node, except the root, has exactly one parent. Every node may give rise to zero or more child nodes. A binary tree restricts the number of children per node to a maximum of two. Degenerate trees have only a single pathway from root to its one leaf.
Expert Systems: Principles and Programming, Fourth Edition 7 Figure 3.1 Binary Tree

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Expert Systems: Principles and Programming, Fourth Edition 8 Graphs Graphs are sometimes called a network or net. A graph can have zero or more links between nodes – there is no distinction between parent and child. Sometimes links have weights – weighted graph; or, arrows – directed graph. Simple graphs have no loops – links that come back onto the node itself.
Expert Systems: Principles and Programming, Fourth Edition 9 Graphs A circuit (cycle) is a path through the graph beginning and ending with the same node. Acyclic graphs have no cycles. Connected graphs have links to all the nodes. Digraphs are graphs with directed links. Lattice is a directed acyclic graph.

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Expert Systems: Principles and Programming, Fourth Edition 10 Figure 3.2 Simple Graphs
11 Making Decisions Trees / lattices are useful for classifying objects in a hierarchical nature. Trees / lattices are useful for making decisions. We refer to trees / lattices as structures. Decision trees are useful for representing and

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chapter03 - Chapter 3 Methods of Inference Expert Systems...

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