On the k-Boundedness for Existential Rules

The chase is a fundamental tool for existential rules. Several chase variants are known, which differ on how they handle redundancies possibly caused by the introduction of nulls. Given a chase variant, the halting problem takes as input a set of existential rules and asks if this set of rules ensures the termination of the chase for any factbase. It is well-known that this problem is undecidable for all known chase variants. The related problem of boundedness asks if a given set of existential rules is bounded, i.e., whether there is a predefined upper bound on the number of (breadth-first) steps of the chase, independently from any factbase. This problem is already undecidable in the specific case of datalog rules. However, knowing that a set of rules is bounded for some chase variant does not help much in practice if the bound is unknown. Hence, in this paper, we investigate the decidability of the k-boundedness problem, which asks whether a given set of rules is bounded by an integer k. We prove that k-boundedness is decidable for three chase variants, namely the oblivious, semi-oblivious and restricted chase.Comment: 20 pages, revised version of the paper published at RuleML+RR 201

Interval temporal logic model checking: The border between good and bad HS fragments

The model checking problem has thoroughly been explored in the context of standard point-based temporal logics, such as LTL, CTL, and CTL 17, whereas model checking for interval temporal logics has been brought to the attention only very recently. In this paper, we prove that the model checking problem for the logic of Allen\u2019s relations started-by and finished-by is highly intractable, as it can be proved to be EXPSPACE-hard. Such a lower bound immediately propagates to the full Halpern and Shoham\u2019s modal logic of time intervals (HS). In contrast, we show that other noteworthy HS fragments, namely, Propositional Neighbourhood Logic extended with modalities for the Allen relation starts (resp., finishes) and its inverse started-by (resp., finished-by), turn out to have\u2014maybe unexpectedly\u2014the same complexity as LTL (i.e., they are PSPACE-complete), thus joining the group of other already studied, well-behaved albeit less expressive, HS fragments

Physical Electronics

Contains reports on three research projects

Physical Electronics

Contains reports on three research projects

Feeding the crusades: archaeobotany, animal husbandry and livestock alimentation on the Baltic frontier

The integrated results of micromorphology, plant macrofossil, pollen, phytolith, and non-pollen palynomorph analyses represent an important study of two thirteenth-century Teutonic Order castles at Karksi (Livonia), and Elbląg (Prussia). The research examines deposits that formed during the period of active crusading. At Karksi, the investigation of a midden and of the organic-rich sediment beneath allows the diachronic use of this area to be understood. Freshwater aquatic indicators are consistent with the occurrence of shallow stagnant water, as also suggested by a waterlaid pond sediment identified in thin-section. Coprophilous spore taxa suggest the use of the pond as a watering hole. Plant macrofossils from the midden represent a range of habitats, mostly from wet/damp areas, as well as pastures and meadows, and also woodlands. Fragments of millet are embedded within herbivore dung in thin-section showing the use of this grain as fodder. At Elbląg, parasite ova may derive from animal feces as they also occur in the dung observed in thin-section, and a range of coprophilous fungal spore taxa were extracted. The results reveal information about the range of livestock that the Teutonic Knights kept, whereabouts within the castles the animals were stabled, and what fodder was used