In this paper, we extend the Disclosure Monitor (DiMon) security mechanism (Brodsky et al. [I]) to prevent illegal inferences via database constraints in dynamic databases. We study updates from two perspectives: 1) updates on tuples that were previously released to a user may cause that tuple to be "outdated", tbus providing greater freedom for releasing new tupies; 2) observation of changes in released tuples may create cardinality based inferences, which are not indicated by database dependencies. We present a mechanism, called Update Consolidator (UpCon) that propagates updates to the user's history file to ensure that no query is rejected based on outdated data. We also propose a Cardinality Inference Detection (CID) module, that generates all data that can be disclosed via cardinality based attacks. We show that UpCon and CID, when integrated into the DiMon architecture, guarantee conjidentiality (completeness property ofthe data-dependent disclosure inference aIgorithm) and maximal availability (soundness property of the data-dependent disclosure inference algorithm) even in the presence of updates.

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Results of searches using a variety of query formulations with several Internet search engines show that strategies intended to give narrower and more precise results may not give improvements in precision even though they result in fewer hits. Searches were performed by students in graduate information retrieval courses using different formulations for the same topic.