It is shown that the existential theory of G with rational constraints, over an HNN-extension G = 〈H, t; tat = φ(a)(a ∈ A)〉 is decidable, provided that the same problem is decidable in the base group H and that A is a finite group. The positive theory of G is decidable, provided that the existential positive theory of G is decidable and that A and φ(A) are proper subgroups of the base group H w...

We present the architecture and design details of a logic database system that extends functionality in a number of ways. The system supports indefinite (non-Horn) facts in extensional database (EDB) and existential quantification in intensional database (IDB) rules. Semantic query optimization is integrated as part of the query processing module. The system also deals with efficient rule manag...

Bedside psychotherapy with medically ill patients can help counter their demoralization, which is the despair, helplessness, and sense of isolation that many patients experience when affected by illness and its treatments. Demoralization can be usefully regarded as the compilation of different existential postures that position a patient to withdraw from the challenges of illness. A fruitful in...

We establish connections between the size of circuits and formulas computing monotone Boolean functions and the size of firstorder and nonrecursive Datalog rewritings for conjunctive queries over OWL2QL ontologies. We use known lower bounds and separation results from circuit complexity to prove similar results for the size of rewritings that do not use non-signature constants. For example, we ...

Existential rules have been proposed for representing on-tological knowledge, specifically in the context of Ontology-BasedQuery Answering. Entailment with existential rules is undecidable.We focus in this paper on conditions that ensure the terminationof a breadth-first forward chaining algorithm known as the chase.First, we propose a new tool that allows to extend existing...

This paper investigates some fundamental properties of 2-way alternating multi-counter automata (2amca’s) with only existential (universal) states which have sublinear space and 1 inkdot. It is shown that for any function s(n) ≥ log n such that log s(n) = o(log n), s(n) space-bounded 1-inkdot 2amca’s with only existential states are incomparable with the ones with only universal states, and the...

We are interested in the kind of well-being that can occur as a person approaches death; we call it "existential maturity." We describe a conceptual model of this state that we felt was realized in an individual case, illustrating the state by describing the case. Our goal is to articulate a generalizable, working model of existential maturity in concepts and terms taken from fundamentals of ps...

This study examined concurrent influences on the will to live in 189 patients with end-stage cancer The authors found significant correlations between the will to live and existential, psychological, social, and, to a lesser degree, physical sources of distress. Existential variables proved to have the most influence, with hopelessness, burden to others, and dignity entering into the final mode...

We study conjunctive query answering and first-order rewritability of conjunctive queries for binary guarded existential rules. In particular, we prove that the problem of establishing whether a given set of binary guarded existential rules is such that all conjunctive queries admit a first-order rewriting is decidable, and present a technique for solving this problem. These results have a impo...