Patrick C. Fischer

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Nondeterminism is one of the most elusive concepts in computing. In this paper we direct our efforts towards viewing nondeterminism as an additional resource at the disposal of time or space bounded Turing machine computations and study the classes of languages acceptable by these machines with <underline>restricted</underline> amounts of nondeterminism. (More)
The languages recognizable by time- and space-restricted multiple-counter machines are compared to the languages recognizable by similarly restricted multipletape Turing machines. Special emphasis is placed on languages definable by machines which operate in “real time”. Time and space requirements for counter machines and Turing machines are analyzed. A(More)
Introduction. Weak multivalued dependencies (WlVDs) mre introduced by Jaeschke ind Scheck in order to characterize when twc NEST operations on different single attributes muld conmute [JSI. Thomas extended this result to nesting cn arbitrary structures and also gave a graph-theoretic characterization [Tl. In this paper we give additional characterizations(More)
We consider relations not in lirst normal form, i.e., a data item in a relation may itself be a relation, and extend the relational algebra to include the restructuring operators NEST and UNNEST. Algebraic characterizations are given for the classes of normalization-lossless relations (obtainable by restructuring flat relations), the nested flat relations(More)