Parallelism in logic programs

This paper presents methods to concurrently exploit AND and OR parallelism in logic programs. The execution sequence of the system is driven by the demand to reduce complexity. The concept of environment copying is applied to achieve modularity when OR parallelism is exploited. As a result, multiple independent structures can be dynamically constructed according to the data dependency to solve various systolic algorithms.

In this paper, we present a method for bottom-up evaluation of Datalog programs in deductive databases that “pushes” derived facts immediately to other rules where they are used for deriving more facts. In this way, the materialization of derived relations is avoided as far as possible. Derived facts are represented by values in variables and a location in the program, and not as explicitly constructed tuples. This helps to avoid copying operations and to keep the actively used memory small to make better use of modern processors. The method can be quite easily explained by translating Datalog to functions in a standard programming language like C++ and then using optimizations of the C++ compiler like inlining. First performance tests with benchmarks from the OpenRuleBench collection give good results. This is interesting because systems based on SLD-resolution with tabling such as XSB have beaten older deductive database implementations based on bottom-up evaluation. Now it seems that bottom-up evaluation can be done in a very competitive way.

We show how the language Constraint Handling Rules (CHR), a high-level logic language for the implementation of constraint solvers, can be slightly extended to become a general-purpose logic programming language with an expressive power subsuming the expressive ower of Horn clause programs with SLD resolution. The extended language, called “CHR∀”, retains however the extra features of CHR, e.g., committed choice and matching, which axe important for other purposes, especially for efficiently solving constraints. CHR∀ turns out to be a very flexible query language in the sense that it supports several (constraint) logic programming paradigms and allows to mix them in a single program. In particular, it supports top-down query evaluation and also bottom-up evaluation as it is frequently used in (disjunctive) deductive databases.

The term "Logic Programming" refers to a variety of computer languages and execution models which are based on the traditional concept of Symbolic Logic. The expressive power of these languages offers promise to be of great assistance in facing the programming challenges of present and future symbolic processing applications in Artificial Intelligence, Knowledge-based systems, and many other areas of computing. The sequential execution speed of logic programs has been greatly improved since the advent of the first interpreters. However, higher inference speeds are still required in order to meet the demands of applications such as those contemplated for next generation computer systems. The execution of logic programs in parallel is currently considered a promising strategy for attaining such inference speeds. Logic Programming in turn appears as a suitable programming paradigm for parallel architectures because of the many opportunities for parallel execution present in the implementation of logic programs. This dissertation presents an efficient parallel execution model for logic programs. The model is described from the source language level down to an "Abstract Machine" level suitable for direct implementation on existing parallel systems or for the design of special purpose parallel architectures. Few assumptions are made at the source language level and therefore the techniques developed and the general Abstract Machine design are applicable to a variety of logic (and also functional) languages. These techniques offer efficient solutions to several areas of parallel Logic Programming implementation previously considered problematic or a source of considerable overhead, such as the detection and handling of variable binding conflicts in AND-Parallelism, the specification of control and management of the execution tree, the treatment of distributed backtracking, and goal scheduling and memory management issues, etc. A parallel Abstract Machine design is offered, specifying data areas, operation, and a suitable instruction set. This design is based on extending to a parallel environment the techniques introduced by the Warren Abstract Machine, which have already made very fast and space efficient sequential systems a reality. Therefore, the model herein presented is capable of retaining sequential execution speed similar to that of high performance sequential systems, while extracting additional gains in speed by efficiently implementing parallel execution. These claims are supported by simulations of the Abstract Machine on sample programs.

Reviewed by: Remembering Papua New Guinea: An Eccentric Ethnography Dan Jorgensen Remembering Papua New Guinea: An Eccentric Ethnography, by William C Clarke. Canberra: Pandanus Books and Research School of Pacific and Asian Studies, Australian National University, 2003. ISBN 1-74076-034-4; viii + 176 pages, figures, maps, photographs, notes, bibliography. A$49.50 (includes GST). When Australian administration was extended through the relatively poorly known highlands of New Guinea after the Second World War, it wasn't long before the first wave of ethnographers followed in the patrol officers' wake. The region became a testing ground for some of the day's latest anthropological ideas, and many viewed the highlands as a laboratory for ethnographic analysis. A number of coordinated research programs were launched, and none was more ambitious than A P Vayda's project on "Human Ecology in the New Guinea Rainforest." Set among the Maring of the Jimi and Simbai Valleys, the project gave rise to a number of studies of the relation of the Maring to their environment, including Roy Rappaport's famous Pigs for the Ancestors (1968). Trained both as an anthropologist and geographer, Bill Clarke joined the project in 1964. Originally brought in with fellow geographer John M Street, Clarke undertook survey work to assess agricultural practices, land use, and the possible effects of resource constraints on Maring culture and behavior. He then stayed on among a small Maring group, the Bomagai-Angoiang, and completed the research that he published in his own book on the Maring, Place and People (1971). Clarke's stay among the Maring also yielded a large photographic archive. When the film began to deteriorate in the 1990s, he began salvaging his photographs with digital technology, a process that triggered many of the memories he recalls in this book, written nearly four decades after his original visit. True to its title, the book's organization is eccentric—a cross between a glossy picture book and a collection of short ethnographic notes. It has upwards of sixty color plates, mostly of the Bomagai-Angoiang. The photos are often striking, but the tone is unspectacular and quiet, the collection offering a combination of individual portraits, scenes from everyday life, and landscape shots illustrating the context of Maring livelihood. This works well to foster a mood of nostalgia for a past marked by subsistence affluence and few of the troubles that fill accounts of PNG life today. Each photograph is paired with a page of text. Sometimes Clarke is content to simply describe the photograph, place it in context, and offer a few relevant observations, as when he tells us that a raised cooking platform is more convenient but less efficient than an earth oven (32), or that ringworm can render an otherwise pretty young woman unattractive to potential suitors (78). Occasionally, especially at the beginning of the book, he rhetorically addresses his comments to particular individuals whose photos appear on the facing pages. More often, however, he uses the photographs as points of departure for reflections that tack back and forth between academic debates and contemporary concerns about the environment, [End Page 176] development, and the situation of the Maring and people like them. Melanesianists will recognize certain themes that reprise some of Clarke's contributions to earlier ethnographic discussions, such as his argument that episodes of madness in the New Guinea highlands often have a theatrical quality in which temporarily crazy individuals and their neighbors seem to be in cahoots with one another (124). Beyond that, much of the book can be read as a relaxed but pointed conversation with other Maring ethnographers (Roy Rappaport, Georgeda Buchbinder, Chris Healey, Edward LiPuma, and A P Vayda) concerning their overlapping projects. By far the most important talking point is the significance ofenvironmental limitations in understanding Maring culture. One of Clarke's key contributions to ecological anthropology was a debunking of the notion of "carrying capacity," a seemingly hard-edged concept that proved to be as mushy as they come. His work among the Maring and other New Guinea peoples showed that local productive systems are extremely elastic because people have a large repertoire of techniques of intensification that can effectively push back apparent...

Proximate drivers of population inter-annual variation in seed output for a masting conifer species

People experiencing homelessness are often absent from the development and implementation of new housing projects. As mounting evidence demonstrates the link between health and housing, it seems ineffective to design solutions without the participation and insight of those who are chronically unhoused. This study describes a method for program and product evaluation that people with lived experience of homelessness can use to determine the value of new offerings and then design improvements based on their evaluation. Specifically, this article reports the experience of evaluating a handbook describing the operations of a new type of housing for people experiencing homelessness. The research team, which included people with lived experience of homelessness, performed interviews to evaluate plans in the handbook, analyzed those results, and designed improvements in the operations of the housing based on the program evaluation. The team utilized participatory analysis of the interview data and then used a Human-Centered Design approach to generate ideas based on the analysis and develop concepts to improve the operational plan. The evaluation identified four high-priority problems with the operational plan and the group then designed three unique solutions to address those problems. This project demonstrates that people with lived experience of homelessness can participate as equal partners in the evaluation of a program and the subsequent program improvement design that was based on their evaluations.

Given a set of Datalog rules, facts, and a query, answers to the query can be inferred bottom-up starting with the facts or top-down starting with the query. The dominant strategies to improve the performance of answering queries are reusing answers to subqueries for top-down methods, and transforming rules based on demand from the query, such as the well-known magic sets transformation, for bottom-up methods. However, the performance of these strategies vary drastically, and the most effective method has remained unknown.

In machine work, the productivity, energy efficiency, and the quality of the work depend strongly on the skills of the human operator. This paper proposes a hierarchical method for skill evaluation of human operators in machine work during their normal work. The method refines skill metrics obtained from work cycle recognition-based evaluation system proposed earlier by the authors. The proposed skill components are: machine controlling skills, control parameter tuning skills, knowledge of the work technique and strategy, and planning and decision making skills. The skill components in each task are evaluated by a dedicated fuzzy inference system, whose rule base is generated automatically. The method is utilized to evaluate skills of nine operators of a cut-to-length forest harvester.

As discussed in previous chapters, there are limitations in the existing methods of cost benefit analysis. For economic evaluation of health programs to be useful and meaningful, certain adjustments are needed- Omission of extra-welfaristic elements in social costs and social benefits, inappropriate measures of benefits, difficulties in measuring benefits and a lack of proper integration of cost benefit analysis methods of health programs with the underlying evaluation processes which make it difficult to understand how the cost benefit analysis is being used for social choices, narrow the scope of analysis. An evaluation method needs to be developed on the basis of the right and relevant principles of welfare economics and social choice theory (by explicating social preferences), so that it can test the economic and social efficiency of health programs, containing the benefits and costs which are measured adequately and appropriately. Extra-welfaristic considerations (such as equity, freedom, and so on) in ethics, incorporated in the integrated operational framework and methods of cost benefit analysis, can then be applied in the evaluation.KeywordsSocial WelfareSocial ChoiceWelfare EconomicSocial Welfare FunctionShadow PrexThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Pruning operators, such as cut, are important to develop efficient logic programs as they allow programmers to reduce the search space and thus discard unnecessary computations. For parallel systems, the presence of pruning operators introduces the problem of speculative computations. A computation is named speculative if it can be pruned during parallel evaluation, therefore resulting in wasted effort when compared to sequential execution. In this work we discuss the problems behind the management of speculative computations in or-parallel tabled logic programs. In parallel tabling, not only the answers found for the query goal may not be valid, but also answers found for tabled predicates may be invalidated. The problem here is even more serious because to achieve an efficient implementation it is required to have the set of valid tabled answers released as soon as possible. To deal with this, we propose a strategy to deliver tabled answers as soon as it is found that they are safe from being pruned, and present its implementation in the OPTYap parallel tabling system.

The basic sequential rule induction algorithm does not define a specific class order. Class order is generally selected based on heuristics. We have implemented the basic rule induction algorithm together with several discretization and evaluation methods and varying class orders. Tests in several basic data sets show that the class order considerably influences the resulting accuracy of sequential rule induction. While the class order sometimes has a higher influence than the tested rule quality measures (FOIL and Likelihood Ratio) and the simple discretization algorithms, there is no single class order that provides best results for all tested combinations of discretization and rule quality measure approaches in all cases.

Traditional database query languages such as datalog and SQL allow the user to specify only mandatory requirements on the data to be retrieved from a database. In many applications, it may be natural to express not only mandatory requirements but also preferences on the data to be retrieved. Lacroix and Lavency10) extended SQL with a notion of preference and showed how the resulting query language could still be translated into the domain relational calculus. We explore the use of preference in databases in the setting of datalog. We introduce the formalism of preference datalog programs (PDPs) as preference logic programs without uninterpreted function symbols for this purpose. PDPs extend datalog not only with constructs to specify which predicate is to be optimized and the criterion for optimization but also with constructs to specify which predicate to be relaxed and the criterion to be used for relaxation. We can show that all of the soft requirements in Reference10) can be directly encoded in PDP. We first develop anaively-pruned bottom-up evaluation procedure that is sound and complete for computing answers to normal and relaxation queries when the PDPs are stratified, we then show how the evaluation scheme can be extended to the case when the programs are not necessarily stratified, and finally we develop an extension of themagic templates method for datalog14) that constructs an equivalent but more efficient program for bottom-up evaluation.

The estimation and control of resource usage is now an important challenge in an increasing number of computing systems. In particular, requirements on timing and energy arise in a wide variety of applications such as internet of things, cloud computing, health, transportation, and robots. At the same time, parallel computing, with (heterogeneous) multi-core platforms in particular, has become the dominant paradigm in computer architecture. Predicting resource usage on such platforms poses a difficult challenge. Most work on static resource analysis has focused on sequential programs, and relatively little progress has been made on the analysis of parallel programs, or more specifically on parallel logic programs. We propose a novel, general, and flexible framework for setting up cost equations/relations which can be instantiated for performing resource usage analysis of parallel logic programs for a wide range of resources, platforms, and execution models. The analysis estimates both lower and upper bounds on the resource usage of a parallel program (without executing it) as functions on input data sizes. In addition, it also infers other meaningful information to better exploit and assess the potential and actual parallelism of a system. We develop a method for solving cost relations involving the max function that arise in the analysis of parallel programs. Finally, we instantiate our general framework for the analysis of logic programs with Independent And-Parallelism, report on an implementation within the CiaoPP system, and provide some experimental results. To our knowledge, this is the first approach to the cost analysis of parallel logic programs.

A parallel program is deterministic if it produces the same output on every execution with a given input, regardless of the parallel schedule chosen. Determinism makes parallel programs much easier to write, understand, debug, and maintain. Further, many parallel programs are intended to be deterministic. Therefore a deterministic programming model (i.e., one in which all programs that pass compile-time checking are guaranteed to run deterministically) is attractive. However, aliasing poses difficulties for such a model, because hidden read-write conflicts through shared memory can cause unwanted nondeterminism and even data races. This article surveys the state of the art in program annotations for controlling aliasing in a way that can support a deterministic parallel programming model. It discusses the following techniques: the Deterministic Parallel Java effect system; other effect systems, including systems based on object ownership; permission-based type systems; and annotations based on program logic.