关键词: 网络传输代价, 查询时间, 局部处理代价, 代价函数

Abstract: A new cost model of distributed database query based on the study of availability semi-joins is put forward in this paper，which can describe the cost of distributed database query precisely by including selection of relation copies，query order of multi-join，determination of performance sites，transaction of data and cost of local computation.Then the cost model is analyzed，designed in detail and realized.

Key words: net cost, query time, local cost, cost function