There are six chapters in this paper . the concept of hetergensous databases and the importance of data exchange among hetergeneous databases are illustrated in the first chapter . the adopted technology of hetergeneous databases exchange is introduced in the second chapter . and the idea exploring xml implementing hetergeneous databases exchange is proposed . the development of xml and its application are reviewed and the relation of the logical structure of xml and dtd and schema is analyzed in the third chapter . the structure of the system exploring middleware tecknology implementing data exchange among hetergeneous databases is investigated in the fifth chapter . conclusion is given in the sisth chapter as a summary for this paper 全文共分六章：第一章阐述了异构数据库的概念以及异构数据库间数据交换的重要性；第二章介绍了通常情况下异构数据库间数据交换所采用的各种技术，在此基础上提出了利用xml实现异构数据库间数据交换的思想；第三章回顾了xml的发展历程和其主要应用领域，分析了xml的逻辑构成以及dtd和schema的关系；第四章介绍了xml数据库的基本概念和相关技术并对其使用方法进行了分析；第五章介绍了利用xml中间件技术实现异构数据库间数据交换时的系统结构以及中间件的实现；第六章对全文进行了总结。
