Estimating record selectivitiesEstimating record selectivities Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2015-11-251983enIn this paper we examine the problem of modelling data base contents and user requests. This modelling is necessary in analytic data base performance evaluation studies in order to estimate the number of records of a file that have to be retrieved in response to user(s) requests. The cpu, io, and telecommunication costs of the system are directly or indirectly expressed in terms of these quantities. We first show that certain assumptions-used for modelling data base contents, data placement on devices and user requests often are not satisfied in actual data base environments. Thereafter we provide more detailed modelling techniques based on a multivariate statistical model, and we demonstrate their use in improving data base performance.http://creativecommons.org/licenses/by/4.0/Information Systems 82105-115 Christodoulakis Stavros Χριστοδουλακης Σταυρος Elsevier Information Systems