Transformation-Based Bottom-Up Computation of the Well-Founded Model

We present a framework for expressing bottom-up algorithms to compute the well-founded model of non-disjunctive logic programs. Our method is based on the notion of conditional facts and elementary program transformations studied by Brass and Dix for disjunctive programs. However, even if we restrict their framework to nondisjunctive programs, their residual program can grow to exponential size, whereas for function-free programs our program remainder is always polynomial in the size of the extensional database (EDB). We show that particular orderings of our transformations (we call them strategies) correspond to well-known computational methods like the alternating fixpoint approach, the well-founded magic sets method and the magic alternating fixpoint procedure. However, due to the confluence of our calculi, we come up with computations of the well-founded model that are provably better than these methods. In contrast to other approaches, our transformation method treats magic set transformed programs correctly, i.e. it always computes a relevant part of the well-founded model of the original program.Comment: 43 pages, 3 figure

Experimental Analysis of a 4-Qubit Cluster State

Linear optics quantum logic operations enabled the observation of a four-photon cluster state. We prove genuine four-partite entanglement and study its persistency, demonstrating remarkable differences to the usual GHZ state. Efficient analysis tools are introduced in the experiment, which will be of great importance in further studies on multi-particle entangled states.Comment: 5 pages, 4 figures, submitte

Multimode quantum interference of photons in multiport integrated devices

We report the first demonstration of quantum interference in multimode interference (MMI) devices and a new complete characterization technique that can be applied to any photonic device that removes the need for phase stable measurements. MMI devices provide a compact and robust realization of NxM optical circuits, which will dramatically reduce the complexity and increase the functionality of future generations of quantum photonic circuits

A Distinctive Pd-Hg Signature in Detrital Gold Derived from Alkalic Cu-Au Porphyry Systems

This study comprises the first systematic classification of native gold geochemistry within alkalic porphyry Cu-Au systems and the placer expression of such systems. The geochemistry and mineral associations of gold from four alkalic porphyry deposits in British Columbia, Canada (Afton, Mount Milligan, Mount Polley and Copper Mountain) have been compared to comment on the likely detrital gold expression of similar systems globally. Populations of gold grains collected from in situ hypogene mineralization as well as fluvial deposits downstream of these deposits have been characterized in terms of their alloy composition (Au, Ag, Cu, Hg, and Pd) and associated mineral inclusions. These data are combined to generate a ‘microchemical signature’. Gold compositions vary according to the alteration zone within a porphyry system. Previous compositional studies of gold in porphyry systems have focused on the most economically important ore associated with potassic alteration, wherein native gold hosted either by bornite or chalcopyrite comprises tiny blebs (typically 5-20 μm), containing detectable Cu in the gold alloy to a maximum of around 5% but quite variable (2-30 wt.%) Ag. The presence of such grains have been confirmed in hypogene ore from the four systems studied, but they have been shown to be compositionally distinct from detrital gold collected from nearby fluvial placers which exhibit a strong Pd and Hg signature, both in the alloy and as mineral inclusions. Several workers have described late stage veins associated with alkalic porphyries which contain distinctive Pd-Hg bearing minerals in association with other sulphides and sulphosalts. This unusual mineralogy has been observed in the mineral inclusion suites of populations of detrital gold grains collected in the environs of the porphyry systems. We conclude that whilst the micron-scale Cu-rich gold grains formed in potassically altered rocks are in general too small to be recovered during routine sediment sampling, those formed in later stage hydrothermal systems are larger, and exhibit a distinctive microchemical signature which may be differentiated from those of gold formed in other mineralizing systems. Consequently, compositional studies of detrital gold could underpin a mineral indicator methodology in the exploration for alkalic porphyry Cu-Au deposits

Flexible Computation of the Well-Founded Semantics of Normal Logic Programs

The development and maintenance of modern information systems, that are getting more and more complex and, at the same time, require a high flexibility, is a great challenge for current information and communication technology. One contribution is the usage of a rule-based specification mechanism that allows the compact and declarative description of complex situations. One such rule language is given by normal logic programs. The well-founded semantics has been accepted as the most relevant semantics for logic-based information systems. It assigns a unique (partial) model to every normal logic program, i.e., it allows specifications using any kind of recursion including cyclic positive and negative dependencies. Further, the time complexity of computing the well-founded model of a given intensional database is polynomial in the size of the extensional database. Several evaluation methods for the well-founded semantics are known. Each of these approaches has its advantages and disadvantages. Thus, for practical applications it will not be sufficient to select one static evaluation algorithm and apply it uniformly to any kind of application. However, it is difficult to combine evaluation methods because they all are based on different data structures, applicable to different classes of programs, or whose control strategies are not compatible. In this work we present a framework based on a set of program transformations that generalizes all major computation approaches using a common data structure and provides a common language to describe their evaluation strategy. We allow strategies from set-oriented bottom-up to single-answer top-down or any combination in this range just by rearranging the order of program transformations using an intuitive regular expression lik..

The deductive database system LOLA

The LOLA system has been designed as the query answering component of a deductive database system and integrates ideas from logic programming and relational query processing. LOLA is based on a clausal logic programming language with function symbols, negation, grouping and aggregation, special predicate