瀑布模型中软件生命周期划分为8个阶段：问题的定义、可行性研究、软件需求分析、系统总体设计、详细设计、编码、测试和运行、维护。8个阶段又可归纳为3个大的阶段：计划阶段、开发阶段和(12)。

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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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