The cost of retrievals in what-if databases

Multiple scenarios are critical to what-if analysis. Alternate versions of a database are required. Each version is manipulated and updated as if it were the real database; however, only differences between the version and the real database are stored. Extensions to relational databases to support alternate versions include hypothetical relations and derived relations with exceptions. This paper introduces independently-updated views (IUVs) for creating multiple scenarios and analyzes the overhead for supporting different types of views and queries. The overhead is minimum for creating what-if scenarios based on aggregate views and on views which are small subsets of the database. In case of views which require retrieval of entire or large portions of base tables, the overhead can be high