This paper contextualises and interprets a text seldom addressed in Anglophone scholarship: De die natali (‘On the birthday’), written by Censorinus to celebrate his patron Caerellius’ birthday in 238 c.e. By exploring both gestation (natalis) and time measurement (dies), the work seeks to elucidate and isolate Caerellius’ birthday in time; it is the ultimate guide to his dies natalis. Despite a seemingly narrow focus, De die natali is best understood as part of a broad ‘spectrum’ of encyclopaedic texts, exemplifying the ‘totalising’ impetus of knowledge ordering in the Roman Empire, while simultaneously exposing the limits of such efforts. An interlocking set of tensions underlie the text, which resonate with other encyclopaedic projects — tensions between unity and plurality, centre and periphery, and the relationship between nature and culture. De die natali is both a product of, and commentary on, the conditions of human knowledge and the Empire's cultural diversity in the early third century.

Answer Set Programming (ASP) is a well-known declarative formalism in logic programming. Efficient implementations made it possible to apply ASP in many scenarios, ranging from deductive databases applications to the solution of hard combinatorial problems. State-of-the-art ASP systems are based on the traditional ground&solve approach and are general-purpose implementations, i.e., they are essentially built once for any kind of input program. In this paper, we propose an extended architecture for ASP systems, in which parts of the input program are compiled into an ad-hoc evaluation algorithm (i.e., we obtain a specific binary for a given program), and might not be subject to the grounding step. To this end, we identify a condition that allows the compilation of a sub-program, and present the related partial compilation technique. Importantly, we have implemented the new approach on top of a well-known ASP solver and conducted an experimental analysis on publicly-available benchmarks. Results show that our compilation-based approach improves on the state of the art in various scenarios, including cases in which the input program is stratified or the grounding blow-up makes the evaluation unpractical with traditional ASP systems.

In this article, three important issues in organizational multilevel research are discussed and clarified, namely: (a) The interpretation of “cross-level direct effects” in theoretical and research multilevel models, (b) the specification of the emergence processes involved in higher-level constructs, and (c) the sample size recommendations for using multilevel statistical methods. By doing so, this article hopes to contribute to the improvement of organizational multilevel research.

Gelfond and Zhang recently proposed a new stable model semantics based on Vicious Circle Principle in order to improve the interpretation of logic programs with aggregates. The paper focuses on this proposal, and analyzes the complexity of both coherence testing and cautious reasoning under the new semantics. Some surprising results highlight similarities and differences versus mainstream stable model semantics for aggregates. Moreover, the paper reports on the design of compilation techniques for implementing the new semantics on top of existing ASP solvers, which eventually lead to realize a prototype system that allows for experimenting with Gelfond-Zhang's aggregates.

In order to achieve competitive performance, abstract machines for Prolog and related languages end up being large and intricate, and incorporate sophisticated optimizations, both at the design and at the implementation levels. At the same time, efficiency considerations make it necessary to use low-level languages in their implementation. This makes them laborious to code, optimize, and, especially, maintain and extend. Writing the abstract machine (and ancillary code) in a higher-level language can help tame this inherent complexity. We show how the semantics of most basic components of an efficient virtual machine for Prolog can be described using (a variant of) Prolog. These descriptions are then compiled to C and assembled to build a complete bytecode emulator. Thanks to the high-level of the language used and its closeness to Prolog, the abstract machine description can be manipulated using standard Prolog compilation and optimization techniques with relative ease. We also show how, by applying program transformations selectively, we obtain abstract machine implementations whose performance can match and even exceed that of state-of-the-art, highly-tuned, hand-crafted emulators.

In prior work, we showed that logic programming compilation can be given a proof-theoretic justification for generic abstract logic programming languages, and demonstrated this technique in the case of hereditary Harrop formulas and their linear variant. Compiled clauses were themselves logic formulas except for the presence of a second-order abstraction over the atomic goals matching their head. In this paper, we revisit our previous results into a more detailed and fully logical justification that does away with this spurious abstraction. We then refine the resulting technique to support well-moded programs efficiently.

Control flow compilation is a hybrid between classical WAM compilation and meta-call, limited to the compilation of non-recursive clause bodies. This approach is used successfully for the execution of dynamically generated queries in an inductive logic programming setting (ILP). Control flow compilation reduces compilation times up to an order of magnitude, without slowing down execution. A lazy variant of control flow compilation is also presented. By compiling code by need, it removes the overhead of compiling unreached code (a frequent phenomenon in practical ILP settings), and thus reduces the size of the compiled code. Both dynamic compilation approaches have been implemented and were combined with query packs, an efficient ILP execution mechanism. It turns out that locality of data and code is important for performance. The experiments reported in the paper show that lazy control flow compilation is superior in both artificial and real life settings.

The logic programming paradigm provides the basis for a new intensional view of higher-order notions. This view is realized primarily by employing the terms of a typed lambda calculus as representational devices and by using a richer form of unification for probing their structures. These additions have important meta-programming applications but they also pose non-trivial implementation problems. One issue concerns the machine representation of lambda terms suitable to their intended use: an adequate encoding must facilitate comparison operations over terms in addition to supporting the usual reduction computation. Another aspect relates to the treatment of a unification operation that has a branching character and that sometimes calls for the delaying of the solution of unification problems. A final issue concerns the execution of goals whose structures become apparent only in the course of computation. These various problems are exposed in this paper and solutions to them are described. A satisfactory representation for lambda terms is developed by exploiting the nameless notation of de Bruijn as well as explicit encodings of substitutions. Special mechanisms are molded into the structure of traditional Prolog implementations to support branching in unification and carrying of unification problems over other computation steps; a premium is placed in this context on exploiting determinism and on emulating usual first-order behaviour. An extended compilation model is presented that treats higher-order unification and also handles dynamically emergent goals. The ideas described here have been employed in the Teyjus implementation of the $\lambda$Prolog language, a fact that is used to obtain a preliminary assessment of their efficacy.

We introduce a methodology and framework for expressing general preference information in logic programming under the answer set semantics. An ordered logic program is an extended logic program in which rules are named by unique terms, and in which preferences among rules are given by a set of atoms of form s [pr ] t where s and t are names. An ordered logic program is transformed into a second, regular, extended logic program wherein the preferences are respected, in that the answer sets obtained in the transformed program correspond with the preferred answer sets of the original program. Our approach allows the specification of dynamic orderings, in which preferences can appear arbitrarily within a program. Static orderings (in which preferences are external to a logic program) are a trivial restriction of the general dynamic case. First, we develop a specific approach to reasoning with preferences, wherein the preference ordering specifies the order in which rules are to be applied. We then demonstrate the wide range of applicability of our framework by showing how other approaches, among them that of Brewka and Eiter, can be captured within our framework. Since the result of each of these transformations is an extended logic program, we can make use of existing implementations, such as dlv and smodels. To this end, we have developed a publicly available compiler as a front-end for these programming systems.

A number of mitochondrial (mt) tRNAs have strong structural deviations from the classical tRNA cloverleaf secondary structure and from the conventional L-shaped tertiary structure. As a consequence, there is a general trend to consider all mitochondrial tRNAs as “bizarre” tRNAs. Here, a large sequence comparison of the 22 tRNA genes within 31 fully sequenced mammalian mt genomes has been performed to define the structural characteristics of this specific group of tRNAs. Vertical alignments define the degree of conservation/variability of primary sequences and secondary structures and search for potential tertiary interactions within each of the 22 families. Further horizontal alignments ascertain that, with the exception of serine-specific tRNAs, mammalian mt tRNAs do fold into cloverleaf structures with mostly classical features. However, deviations exist and concern large variations in size of the D- and T-loops. The predominant absence of the conserved nucleotides G18G19 and T54T55C56, respectively in these loops, suggests that classical tertiary interactions between both domains do not take place. Classification of the tRNA sequences according to their genomic origin (G-rich or G-poor DNA strand) highlight specific features such as richness/poorness in mismatches or G-T pairs in stems and extremely low G-content or C-content in the D- and T-loops. The resulting 22 “typical” mammalian mitochondrial sequences built up a phylogenetic basis for experimental structural and functional investigations. Moreover, they are expected to help in the evaluation of the possible impacts of those point mutations detected in human mitochondrial tRNA genes and correlated with pathologies.