Perimetry is a commonly used clinical test for visual function, limited by high variability. The sources of this variability need to be better understood. In this paper, we investigate whether noise intrinsic to neural firing could explain the variability in normal subjects. We present the most physiologically accurate model to date for stimulus detection… (More)
PURPOSE Studies in glaucoma patients show that standard automated perimetry results increase in variability as sensitivity decreases. However, the reasons for this change are unclear. This study presents the principle of Divergent Dysfunction as a possible explanation for this change in variability, and incorporates it into a model that can be used to… (More)
The view update problem is concerned with indirectly modifying those tuples that satisfy a view (or derived table) by an appropriate update against the corresponding base tables. The notion of a deduction tree is defined and the relationship between such trees and the view update problem for indefinite deductive databases is considered. It is shown that a… (More)
The computational complexity of a number of problems relating to minimal models of non-Horn deductive databases is considered. In particular, the problem of determining minimal model membership is shown to be NP-complete for non-recursive propositional databases. The structure of minimal models is also examined using the notion of a cyclic tree, and methods… (More)
The relationship between cyclic covers and perfect models of indefinite stratified deductive databases is discussed with respect to query answering, view updates and partial evaluation. The notion of a conjunctive answer to a database query is introduced, and such answers are shown to have a number of advantages over (the more commonly studied) "… (More)
Cyclic covers are shown to characterise disjunctive stable models of unstrati-fied deductive databases, and to facilitate top-down query processing, query compilation and view updating under the disjunctive stable model semantics. Such processing is shown to be more complex than comparable processing of stratified databases.