Describing and deriving certain answers over partial databases

Although there has been much work in recent years on answering queries using views, there has been less work on deriving answers from partial databases. That is given a partial database state D (V) , materialized via the view V, what queries can be asked over D (V) that can be answered with certainty using only the instance of the partial database and standard query evaluation mechanisms. We define these as the derivable answers and show several special cases in which we can compute and intensionally describe them.