But because of the difficulty in resolving schematic heterogeneity, query processing, global transaction management and global view maintenance in multidatabase, there are still a lots of shortage in this research area.
但由于多库系统中实现模式集成、查询语言转换、全局事务管理、全局视图维护等有较大难度，使得在该领域的研究中仍存在不足之处，还有很多技术问题有待进一步解决。
参考来源 - 多数据库系统中关键技术的研究·2,447,543篇论文数据，部分数据来源于NoteExpress
Based on the analysis of view maintenance anomaly, the concurrent updates are found to be one of the main reasons that cause view maintenance anomaly.
通过对视图维护过程中的更新异常进行分析，发现并发更新是导致视图维护异常的主要原因。
Meanwhile, data update and schema change are possible to coexist under the concurrent environment which brings about many problems to view maintenance.
在并发环境下，数据更新和模式更新极有可能同时存在，这对视图维护工作带来极大的困难。
The view maintenance process in the loosely coupled environment was implemented as a conceptual transaction, by the definitions of concurrency dependency and same-source dependency.
通过定义不同数据源更新之间的并发依赖关系和同源依赖关系，利用概念化事务模型可实现松散耦合环境中视图的并发维护。
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