7 research outputs found
FORMAL SEMANTICS FOR TIME IN DATABASES
The concept of an historical database is introduced as a tool for
modelling the dynamic nature of some part of the real world. Just as first-order
logic has been shown to be a useful formalism for expressing and
understanding the underlying semantics of the relational database model,
intensional logic is presented as an analogous formalism for expressing and
understanding the temporal semantics involved in an historical database.
The various components of the relational model, as extended to include
historical relations, are discussed in terms of the model theory for the logic
ILs, a variation of the logic IL formulated by Richard Montague. The
modal concepts of intensional and extensional data constraints and
queries are introduced and contrasted. Finally, the potential application of
these ideas to the problem of Natural Language Database Querying is discussed.Information Systems Working Papers Serie
Optimization of Boolean expressions for main memory database systems
With the ubiquity of main memory databases which are increasingly replacing the old disk-oriented databases, relations are being stored in denormalized form in order to increase the query throughput, thus, the dominance of join operators in terms of costsis being replaced by the costs of evaluating selection predicates. Boolean expressions containing selection predicates connected both conjunctively and disjunctively have been thus far solved by rather simple heuristics which leaves a large optimization potential unharvested.
To exacerbate the matter, such heuristics rely on the independent predicate selectivity assumption which typically does not hold, and the constant predicate costs assumption which in terms of main memory database systems does not hold either.
In this thesis we tackle the problem of optimizing Boolean expressions by not relying on the independence assumption nor the constant predicate costs assumption. We present optimization algorithms for queries containing both conjunctively and disjunctively connected predicates together with a cost model which precisely captures CPU architectural characteristics such as branch misprediction.
Our optimization algorithms achieve the optimum in terms of plan quality, thus, they harvest the entire optimization potential inherent in Boolean expressions
Information resources management, 1984-1989: A bibliography with indexes
This bibliography contains 768 annotated references to reports and journal articles entered into the NASA scientific and technical information database 1984 to 1989