Optimal view caching

A view in a database is a subset of records selected from several files to satisfy some condition, e.g. the join of two relations.It has been shown that it is more efficient to store pointers to the satisfying records of the base relations rather than the complete records of the view. We are interested in efficient caching of such pointers (in effect constructing the view) when the database lies in secondary storage and only a limited number of buffers exists in memory.
A view caching is optimal if it is done with the minimum number of reads from secondary storage. We prove that optimal view caching is NP -complete.