Constraint Handling Rules (CHR) is a high-level programming language based on multi-headed guarded rules. The original highlevel operational semantics of CHR is very nondeterministic. Recently, instantiations of the high-level operational semantics have been proposed and implemented, removing sources of nondeterminism and hence allowing better execution control. Rule guards may be redundant und...

In this paper we describe the intelligent information systems that are used by the Dutch railway operator NS Reizigers for supporting its internal planning processes of generating efficient and robust duties for train drivers and guards. We focus on the TURNI system that provides real active support in creating such duties. The underlying model of the TURNI system is a set covering model with a...

For ML and Haskell, accurate warnings when a function definition has redundant or missing patterns are mission critical. But today’s compilers generate bogus warnings when the programmer uses guards (even simple ones), GADTs, pattern guards, or view patterns. We give the first algorithm that handles all these cases in a single, uniform framework, together with an implementation in GHC, and evid...

Previous ultra-dependable real-time computing architectures have been specialised to meet the requirements of a particular application domain. Over the last two years, a consortium of European companies and academic institutions has been investigating the design and development of a Generic Upgradable Architecture for Real-time Dependable Systems (GUARDS). The architecture aims to be tolerant o...

Most information systems that are driven by process models (e.g., workflow management systems) record events in event logs, also known as transaction logs or audit trails. We consider processes that not only keep track of their history in a log, but also make decisions based on this log. To model such processes we extend the basic Petri net framework with the notion of history and add guards to...

An open edge of a simple polygon is the set of points in the relative interior of an edge. We revisit several art gallery problems, previously considered for closed edge guards, using open edge guards. A guard edge of a polygon is an edge that sees every point inside the polygon. We show that every simple non-starshaped polygon admits at most one open guard edge, and give a simple new proof tha...

We prove that the satisfiability problem for the two-variable guarded fragment with transitive guards GF +TG is 2EXPTIME-hard. This result closes the open questions left in [4], [17]. In fact, we show 2EXPTIME-hardness of minGF + TG, a fragment of GF + TG without equality and with just one transitive relation ≺, which is the only non-unary symbol allowed. Our lower bound for minGF + TG matches ...

We use the concept of pointed pseudo-triangulations to establish new upper and lower bounds on a well known problem from the area of art galleries: What is the worst case optimal number of vertex π -guards that collectively monitor a simple polygon with n vertices? Our results are as follows: 1. Any simple polygon with n vertices can be monitored by at most n/2 general vertex π -guards. This bo...

By definition Timed Automata have an infinite state-space, thus for verification purposes, an exact finite abstraction is required. We propose a locationbased finite zone abstraction, which computes an abstraction based on the relevant guards for a particular state of the model (as opposed to all guards). We show that the location-based zone abstraction is sound and complete with respect to loc...