在只有单重继承的类层次结构中，类层次结构是(23)层次结构。

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Artificial　intelligence (AI) ,an　interdisciplinary　field,　is　usually　regarded　as　a　branch　of　computer　science,　dealing　with　models　and　systems　for　the　performance　of　functions　generally　associated　with　human　intelligence,　such　as(71)and　learning.In　AI,　knowledge-based　system　is　an　information(72)system　that　provides　for　solving　problems　in　a　particular　domain　or　application　area　by　drawing　inferences　from　a　knowledge　base.　Moreover,　some　knowledge-based　systems　have　learning　capabilities.　Expert　system (ES) indicates　the　knowledge-based　system　that　provides　for　solving　problems　in　a　particular　domain　or　application　area　by　drawing　inferences　from　a　knowledge　base　developed　from　human(73).　Some　expert　systems　are　able　to(74)their　knowledge　base　and　develop　new　inference　rules　based　on　their　experience　with　previous　problems.　The　term　"expert　system"　is　sometimes　used(75)with　"knowledge-based　system",　but　should　be　taken　to　emphasize　expert　knowledge.

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