【摘要】 关系数据库中空值存在不同的语义,并且会影响模糊查询结果。针对该问题,提出用标号来区分空值的语义,并且在EPTV逻辑的基础上,对关系运算和一些复杂的嵌套查询进行扩展,给出相关定义和计算方法。通过实例说明,与常规模糊查询相比,该方法能较好地反映空值对模糊查询结果的影响。更多还原

【Abstract】 Null values have different semantics in relational databases and influence the results of fuzzy queries.This paper distinguishes the different semantics of null values and attaches labels to these semantics.Relational operations and the complex nested queries are extended on the base of Extended Possibilistic Truth Values(EPTV) logic.Related definitions and calculation methods are proposed.Instances illuminate that the method can reflect the effects of different null values on query results compared with regular fuzzy queries.更多还原