Abstract: The incomplete information system is taken into consideration，in which unknown values are considered as not only absent but also missing.In this kind of incomplete information system，a new kind of weighted similarity measures based on relative degree is proposed according to the set pair analysis.From what have been discussed above，expressive forms of weighted similarity measures in two special incomplete information systems are investigated，an illustrative example is analyzed to indicate the validity of rough set model based upon set pair analysis.

摘要： 考虑一种不完备信息系统，其中同时具有缺席和遗漏型未知属性值，在这种不完备信息系统中，采用集对分析的方法构建了一种新的基于联系度的加权相似度量。在此基础上，分析了加权相似度量在两种特殊情形的不完备信息系统中的表现形式，并通过实例说明了它的有效性。