UD-Cache: An efficient XML Cache system with upward-validation and downward-evaluation

Caching mechanism is widely used in database systems for improving performance. In this paper, we present a cache system, named UD-Cache, for the maintenance and utilization of cached XML views. To achieve an efficient query processing over cached views, a set of novel criteria on view answerability is proposed. The criteria are more relaxed as compared with the current ones, and hence the hit rate of view selection could be promoted. With these criteria, the answerability checking method which is actually based on suffix-string mapping is proposed to further improve the efficiency. With the mapping method, a two-phase view selection process is developed to efficiently find an appropriate view from the cache. An auxiliary structure is devised for view evaluation. With such a structure, the view evaluation process could be divided into upward validation and downward evaluation. Experimental results demonstrate that the UD-Cache system could bring a substantial performance improvement on view selection and view answering, and achieve a high hit rate as compared to the existing techniques.