Joachim Kröger

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With the substantial change of declarative query languages from plain SQL to the so-called \object SQLs", in particular OQL, there has surprisingly been not much c hange in the way problems of query representation and optimization for such languages are tackled. We i d e n tify some of the diiculties pure algebraic approaches experience when facing object(More)
In query optimization, a given query will be transformed by rewrite rules into an equivalent execution plan that is cheaper than the straightforwardly assigned plan according to some cost model. Finding the cheapest of all equivalent execution plans is a challenge since the rewriting of complex queries on the basis of a large set of rewriting rules may(More)
The conceptual development of the rule{based component of the CROQUE query rewrite and optimization system led to the derivation of an ordering of the rules present in the rule base according to their \optimization potential" in order to increase the eeciency of the logical term rewriting 5]. This heuristic may indeed be used for any other rule{based(More)
Examples of a combined approach using in vivo as well as in vitro methods for the assessment of prenatal toxicity are presented. The topics discussed include the analysis of the possible embryotoxic potential of valproic acid (VPA), female sex hormones, bis(tri-n-butyltin) oxide (TBTO), and acyclovir and the problem of supplementing in vitro systems with(More)