【摘要】 <正> 1 引言数据库中的视图机制主要是根据用户或应用的需要对数据进行剪裁以增加数据库的灵活性。数据库的视图是适合某一特定用户或应用的数据库中部分数据的一种抽象。视图是依照视图声明语言(View Specification Language)来定义的,视图的声明是施加于源数据库(或等价的基数据库)上的。通常,数据库视图既可以是虚拟的(Virtual)、也可以是实际化的更多还原

【Abstract】 In this paper we introduce the view specification language and consider the problem of answering queries posed on semistructured data views. The two main approaches,query rewriting and view materialization,are outlined. We also discuss the views and its maintenance for XML data. Based on the above discussion a view architecture for integrating data from heterogeneous source or from the WWW is proposed.更多还原