The Second-Order Approach and its Application to View-Based Query Processing
- Contact Christoph Wernhard
- since April 1, 2015
- funded by DFG
In the project, an approach to logic-based knowledge processing, to be called here second-order approach, will be investigated. The idea is that expressive representation languages are, on the one hand, available to formulate applications in a very natural way, but on the other hand, are processed by reduction to poorer languages that are better suited for computation. Such reductions are made possible because the expressive language constructs are used in specific application contexts.
Proofs of concept for this approach have been given in the late 90s with the use of second-order quantifier elimination for computing circumscription, and recently with applications of uniform interpolation (which can be expressed as second-order quantifier elimination) in description logics. The approach typically allows to trace concepts from the application area back to fundamental concepts of logic, indicating new application possibilities and parallels between areas that enable transfer and combination of techniques.
The project connects two lines of work that will stimulate each other: (1) Concepts of a particular application area, view-based query processing, will be formally modeled with second-order operators. (2) Computational methods will be developed that realize applications, on the basis of the formalization, essentially by elimination of second-order operators.
The basic idea of view-based query processing is to translate and decompose queries such that multiple agents with specialized knowledge bases and processing capabilities can contribute to answer computation. By its is close relation to definability, a general concept of logic, view-based query processing is well suited to the approach of the project. Central objectives of the project with respect to view-based query processing are semantic clarification of the involved concepts, availability of second-order operator elimination to compute query transformations, and generalization beyond databases.
With respect to computational methods, new techniques for second-order operator elimination will be developed, based on propositional logic - related to recent SAT preprocessors, based on first-order logic, and by taking specific formula patterns into account that occur in view-based query processing.
The results of the project should serve as an elaborate formal and automated foundation for a multitude of further applications that are suited for the second-order approach. These include, for example, variants of non-standard inferences, abductive reasoning, modularization of knowledge bases, non-monotonic reasoning, and reasoning about knowledge.
Talks and Miscellaneous