利用约束优化数据库Web视图上的查询

当前，许多大的Web站点的信息和数据呈现出结构化或半结构化的特点，因而可经抽象，作为类似关系数据库或者面向对象数据库并加以处理，以提高操作效率，特别是在此基础上进行的查询操作．但查询这些抽象的结构化或半结构化的视图需要新的技术．由于数据存储比较分散，并且多数以HTML，XML等的形式存放，因而网络访问成为主要的查询代价构成要素．为此通过利用’Web数据库的冗余来减少网络访问．采用数据模型Araneus的一个子集作为数据模型，并利用链接约束、包含约束、范围约束以及多种规则重写关系代数表达式，以期达到优化查询结果的目的。

OPTIMIZING QUERY OF THE DATABASE WEB VIEW USING CONSTRAINTS

The information and data on many large web sites are of structuredness or semi structuredness, which can be abstracted and then processed similarly as relational database or object oriented database to raise the operation efficiency, especially the query efficiency. However, new techniques are required for querying the view of such abstracted structural or semi structural data. Due to the distribution of data, which normally exist in the form of HTML or XML, the access of the web becomes the main factor of the query expense. Therefore, the access of the web may be reduced through using the redundancy of the web database. A subset of the Araneus data model is used in this paper, and also the link constraint, inclusion constraint, scope constraint and several rules rewriting the relational algebraic expressions are used to optimize the query results.