Nowadays, a common problem to which many corporations or organizations face is how to easily and uniformly access over multiple, disparate information sources which includes database, object store, knowledge bases, file system, digital libraries, information retrieval system, and electronic mail system. The goal of a data integration system is to provide a uniform query to a multitude of data sources. The key advantage of a data integration system is that it frees users from having to locate the source relevant to their query, interact with each source independently, and manually combine the local answer from the different source to a global answer results. Although a lot of research in integration systems has been proposed over pass ten years, few work was concentrate on the cache consistency problem in such systems. In this paper, we first survey existing caching approach and later explore s strong cache consistency which is suitable to integration systems.