Given a model of the polymorphic typed lambda calculus based upon a Cartesian closed category K, there will be functors from K to K whose action on objects can be expressed by type expressions and whose action on morphisms can be expressed by ordinary expressions. We show that if T is such a functor then there is a weak initial T -algebra and if, in addition, K possesses equalizers of all subse...

In this paper, we present a multi-layered architecture for spatial and temporal agents. The focus is laid on the declarativity of the approach, which makes agent scripts expressive and well understandable. They can be realized as (constraint) logic programs. The logical description language is able to express actions or plans for one and more autonomous and cooperating agents for the RoboCup (S...

A sartorial query language facilitates the formulation of queries to a (string) database. One step towards an implementation of such a query language can be taken by defining a logical formalism expressing a known solution for the particular problem at hand. The simplicity of the logic is a desired property, because the simpler the logic that the query language is based on, the more efficiently...

In property testing a small, random sample of an object is taken and one wishes to distinguish with high probability between the case where it has a desired property and the case where it is far from having the property. Much of the recent work has focused on graphs. In the present paper three generalized models for testing relational structures are introduced and relationships between these va...

We show that the directed st-connectivity problem cannot be expressed in symmetric Datalog, a fragment of Datalog introduced in [5]. It was shown there that symmetric Datalog programs can be evaluated in logarithmic space and that this fragment of Datalog captures logspace when augmented with negation, and an auxiliary successor relation S together with two constant symbols for the smallest and...

In this paper we will use the following notation. Given a set of positive integers S, we let S(x) denote the number of elements in S that are ≤ x, and we let |S| denote the total number of elements of S. Given two sets of positive integers A and B, we denote the sumset {a + b : a ∈ A, b ∈ B} by A + B; and so, the number of elements in A + B that are ≤ x will be (A + B)(x). For a finite set of i...

It is well-known that every first-order property on words is expressible using atmost three variables. The subclass of properties expressible with only two variables is alsoquite interesting and well-studied. We prove precise structure theorems that characterizethe exact expressive power of first-order logic with two variables on words. Our resultsapply to both the case with and...

We introduce a quadratic programming framework on graphs (which incorporates MAXIMUM-CUT and MAXIMUM-INDEPENDENT-SET) and show that problems which are expressible in the framework can be solved in polynomial time on graphs without long odd cycles.

Timed pushdown automata (tpda) are an expressive formalism combining recursion with a rich logic of timing constraints. We prove that reachability relations tpda expressible in linear arithmetic, generalising Presburger arithmetic and rational arithmetic. The main technical ingredients novel quantifier elimination result for clock constraints (used to simplify the syntax transitions), use diffe...

We study the problem of evolution for Knowledge Bases (KBs) expressed in Description Logics (DLs) of the DL-Lite family. DL-Lite is at the basis of OWL 2 QL, one of the tractable fragments of OWL 2, the recently proposed revision of the Web Ontology Language. We propose some fundamental principles that KB evolution should respect. We review known model and formula-based approaches for evolution...