Maintaining materialized views without accessing base data (Q1115648)

Access to a database through a user view can be serviced quickly when the view is materialized, i.e., the transformed data is explicitly stored. In the presence of database updates, however, the materialized view can be come costly to maintain, often it must be completely rederived from the base data using the view definition. Under some conditions the view can be updated directly given only the view definition, the current contents of the materialized view, and the update operation (still expressed against the base data), without accessing the base data itself. We consider relational views defined by projection, selection, and join. We present necessary and sufficient conditions on the view definition, contents, and update operations for insertions and deletions to be reflected in the view without reference to base data. Because the possibility of such view-based updating is dependent on the current contents of view, we call the update conditionally autonomously computable.