Partial关系上的聚合操作研究

On Aggregate Operations over Partial Relationship

现实世界中存在着许多非精确数据,在数据库系统中一般用Null值表示[2],表明目前不知道该值,显然这种表示丢失了许多信息.Grant总结定义了部分值(partial values)的概念来取代空值,使得关系表中的属性值可以不局限于不可分的原子.一个部分值被定义为一个可能值的有限集,在该有限集中只有一个值为'true”值.

Arbee and Frank defined extended aggregate operations over partial relationship[1]. And they presented aggregate algorithms about COUNT,MIN and MAX. This paper extends their works,designs and implements algorithms of SUM and AVG based on. a single attribute,and SUM ased on groups. The paper analyses algorithm's complexity and verifies algorithms given by us are much better.