双焦点 meaning in English
bifocus
◇双焦点镜片 ultex; 双焦点透镜 bifocal
Examples
- Dual - focus tube
双焦点管 - Third , this dissertation analyzes the complicacy of result size estimation problem for xml structure based query optimization compared to its counterpart in traditionally relational database , and proposes a full - featured result size estimation algorithm for xml query , sxm . for simple path expression query , this dissertation proposes a dynamic synopsis model for xml data based on the concept of f - stable and b - stable , xmap . for complicated path expression query , this dissertation adopts an improved bifocal sampling method for result size estimation
第三，分析了xml结构化查询优化中的查询代价估计问题与传统关系型数据库中的查询代价估计问题的区别，提出了一套完整的xml结构化查询代价估计体系sxm ，包括对简单路径表达进行查询代价估计的动态xml数据统计模型xmap ，对复杂路径表达进行查询代价估计的双焦点例举法，以及对值匹配条件进行查询代价估计的基于小波的多维直方图方法，并能将多种查询表达的查询代价估计结果结合在一起，以给出一个完整的xpath查询的代价估计。