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ÇëÎÊÒ»¸ö·­ÒëÎÊÌâ More general settings for concept definitions have recently received some atten- tion, deriving from attempts to establish formal relationships between Description Logics and other formalisms and from attempts to satisfy a need for increased ex- pressive power. In particular, the admission of cyclic definitions has led to different semantic interpretations of the declarations, known as greatest/least fixed-point, and descriptive semantics. Although it has been argued that different semantics may be adopted depending on the target application, the more commonly adopted one is descriptive semantics, which simply requires that all the declarations be sat- isfied in the interpretation. Moreover, by dropping the requirement that on the left-hand side of a definition there can only be an atomic concept name, one can consider so-called (general) inclusion axioms of the form C v D where C and D are arbitrary concept expressions. Notice that a concept defini- tion can be expressed by two general inclusions. As a result of several theoretical studies concerning both the decidability of and implementation techniques for cyclic TBoxes, the most recent DL systems admit rather powerful constructs for defining concepts. Õâ¶Î»°Ó¦¸ÃÔõô·­Òë,ÌرðÊǺìÉ«±ê¼ÇµÄ´ÊÓïÊÇʲôÒâ˼,Çë¸÷λxdjmÖ¸µãÒ»ÏÂ,ллÁË    Êղؠ  ·ÖÏí   ¶¥(0)