A probability model of uncertainty in data bases

Uncertainty in the contents of a data base can be due to several reasons: errors in the data which is entered, changes in the real data which have not been introduced into the data base in the form of updates, errors in the data collection process, unreliable operation of the computer system, "don´t care" conditions which are purposely left open by the data base designer, etc. The purpose of this paper is to present a formal model of uncertainty in terms of a probabilistic representation of the data base, and to evaluate the effect of this uncertainty on query processing and on the aggregate or summary information which may suffice in many applications. Our model leads to precise quantifiable engineering estimates and to theorems on the robustness of answers to queries as a function of the uncertainty in the data.