1. A system comprising: one or more machine readable media encoded with, a first virtual table corresponding to a first data; a second virtual table corresponding to a second data; a common table that is associated with the first and second virtual tables; a list with information about associations between the first and second virtual tables and the common table; a generating section that, accesses the list to determine the common table is associated with the first virtual table and the second virtual table, rewrites a received database query, which indicates the common table, to generate a first rewritten database query to indicate the first virtual table instead of the common table and to generate a second rewritten database query to indicate the second virtual table instead of the common table, and generates a plurality of access plans that include at least a first access plan for the first rewritten database query and at least a second access plan for the second rewritten database query, wherein each of the plurality of access plans are for either the first rewritten database query or the second rewritten database query; a selecting section that selects one of the plurality of access plans generated by the generating section; a storing section that caches the plurality of access plans generated by the generating section; a managing section that, in response to being notified that the first data has become unavailable, disables those of a plurality of access plans generated for the first rewritten database query, and in response to being notified that the first data has become available, enables those of the plurality of access plans generated for the first rewritten database query; and a monitoring section that, monitors whether or not the first and second data are available, once the first data has become unavailable, notifies the managing section that the first data has become unavailable, and once the first data has become available, notifies the manage section that the first data has become available.