Abstract: Description Logics（short for DLs） are very important for the expression of ontologies，which allow reasoning about individuals and concepts.Typically，DLs can not process the indefinite knowledge existing widely in nature.Based on the cloud model，Cloud-ALC，the extension of the important description logic ALC，is presented to deal with the indefinite knowledge.The syntax and semantic of it are defined，the properties are studied in detail，and the techniques to solving the entailment problem are also presented.Case analysis proves that Cloud-ALC can provide a formal underpinning for the indefinite extension of ontology description languages.

Key words: clould model, enterprise knowledge presentation, Description Logic, indifinite inference

摘要： 描述逻辑是本体的重要表示方式，但只能处理严格的确定性的知识，并不能处理自然界中广泛存在的模糊的和不确定的知识。通过对最基本的描述逻辑ALC进行扩展，提出了能够处理不确定知识的基于本体和云模型不确定描述逻辑：Cloud-ALC，给出了Cloud-ALC的语法和语义及其蕴涵推理关系，研究了Cloud-ALC所具有的相关性质。实例分析说明Cloud-ALC可以为扩展本体描述语言以便能够处理不确定知识提供语义支持。

关键词: 云模型, 企业知识表示, 描述逻辑, 不确定性推理