Beyond depth-first strategies: improving tabled logic programs through alternative scheduling

Journal ArticleTabled evaluation ensures termination for programs with finite models by keeping track of which subgoals have been called. Given several variant subgoals in an evaluation, only the fi rst one encountered will use program-clause resolution; the rest will resolve with the answers generated by the first subgoal. This use of answer resolution prevents infi nite looping that sometimes happens in SLD. Because answers that are produced in one path of the computation may be consumed, asynchronously, in others, tabling systems face an important scheduling choice not present in traditional top-down evaluation: when to schedule answer resolution. This paper investigates alternate scheduling strategies for tabling in a WAM implementation, the SLG-WAM. The original SLG-WAM had a simple mechanism for scheduling answer resolution that was expensive in terms of trailing and choice-point creation. We propose here a more sophisticated scheduling strategy, batched scheduling, which reduces the overheads of these operations and provides dramatic space reduction as well as speedups for many programs. We also propose a second strategy, local scheduling, which has applications to nonmonotonic reasoning, and when combined with answer subsumption, can arbitrarily improve the performance of some programs

Classifying forest stands according to spatial species mingling

Legislature and international treaties increasingly underline the importance of biodiversity and sustainability, hence the need for accurate measurements, regarding the aforementioned concepts. Biodiversity is a comprehensive term, which can be very difficult/costly to measure directly. Therefore, surrogate measures can be used to quantify different aspects of biodiversity. An indicator closely linked to biodiversity in forest ecosystems is forest structure. To quantify different aspects of forest structure metrices from the field of point process statistics can be used. In this study we introduce the new function J(̅r) and evaluate its ability to describe species mingling in forest stands. This is done by incorporating data from 20 fully inventoried stands from different parts of the world. Producing curves from J(̅r) and from the mark mingling function, v(r) which is arguably the most similar established function. The curves are classified in groups based on characteristics. This is done separately for each function to be able to investigate how the groups differ between J(̅r) and v(r) and to see what new information J(̅r) could provide, additional to v(r). This study suggests that the new function of J(̅r) provides additional information to the mark mingling function, mostly related to J(̅r) being based on the nearest neighbour (NN) concept and thus providing more information on local neighbourhoods. This research also points to the value of J(̅r) being potentially more suitable to use on smaller plots, such as those commonly used in forest inventories.I lagstiftning och internationella fördrag betonas vikten av biodiversitet och hållbarhet, vilket medför ett behov av att kunna utföra korrekta mätningar och övervaka utvecklingen, relaterat till förenämnda begrepp. Biodiversitet är en övergripande term, som kan vara väldigt svår och dyr att mäta i sin helhet. Istället för att mäta biodiversitet direkt, kan man genomföra andra mätningar, vars resultat korrelerar med biologisk mångfald. I skogsekosystem är beståndsstrukturen ofta nära kopplad till biodiversitet. Genom att använda sig av mätetal från forskningsområdet point process statistics är det möjligt att kvantifiera olika aspekter av beståndsstruktur. I denna studie introduceras J(̅r), en ny funktion som är baserad på ett existerande mätetal. J(̅r) testas angående hur väl funktionen kan beskriva trädindividers spatiala fördelning i bestånd, med avseende på arttillhörighet. För att åstadkomma detta används data från 20 totalinventerade bestånd, från olika delar av världen. Kurvor från bestånden produceras med den nya funktionen J(̅r), och mark mingling-funktionen, v(r), som antas vara den mest likartade av existerande funktioner. Kurvorna delas därefter in i grupper baserat på egenskaper, detta görs separat för de enskilda funktionerna, med syftet att undersöka hur de resulterade grupperna skiljer sig åt, för J(̅r) och v(r), och för att kunna avgöra vilken ny information som J(̅r) kan tillföra. Denna studie antyder att den nya funktionen J(̅r) genererar delvis skiljaktig information jämfört med v(r), framförallt relaterat till att J(̅r) utgår från varje specifikt träd och jämför arttillhörighet med de närmaste träden i beståndet. J(̅r) kan potentiellt vara lämpligare att använda på små provytor, vilka vanligen används i skogliga inventeringar

Ontology-based infrastructure for intelligent applications

Ontologies currently are a hot topic in the areas of knowledge management and enterprise application integration. In this thesis, we investigate how ontologies can also be used as an infrastructure for developing applications that intelligently support a user with various tasks. Based on recent developments in the area of the Semantic Web, we provide three major contributions. We introduce inference engines, which allow the execution of business logic that is specified in a declarative way, while putting strong emphasis on scalability and ease of use. Secondly, we suggest various solutions for interfacing applications that are developed under this new paradigm with existing IT infrastructure. This includes the first running solution, to our knowledge, for combining the emerging areas of the Semantic Web Services. Finally, we introduce a set of intelligent applications, which is built on top of onologies and Semantic Web standards, providing a proof of concept that the engineering effort can largely be based on standard components.Ontologien sind derzeit ein viel diskutiertes Thema in Bereichen wie Wissensmanagement oder Enterprise Application Integration. Diese Arbeit stellt dar, wie Ontologien als Infrastruktur zur Entwicklung neuartiger Applikationen verwendet werden können, die den User bei verschiedenen Arbeiten unterstützen. Aufbauend auf den im Rahmen des Semantischen Webs entstandenen Spezifikationen, werden drei wesentliche Beiträge geleistet. Zum einen stellen wir Inferenzmaschinen vor, die das Ausführen von deklarativ spezifizierter Applikationslogik erlauben, wobei besonderes Augenmerk auf die Skalierbarkeit gelegt wird. Zum anderen schlagen wir mehrere Lösungen zum Anschluss solcher Systeme an bestehende IT Infrastruktur vor. Dies beinhaltet den, unseres Wissens nach, ersten lauffähigen Prototyp der die beiden aufstrebenden Felder des Semantischen Webs und Web Services verbindet. Schließlich stellen wir einige intelligente Applikationen vor, die auf Ontologien basieren und somit großteils von Werkzeugen automatisch generiert werden können

A grey systems analysis of water quantity allocation and quality protection in Xiamen, China

This study was designed to introduce the concepts of grey systems theory into water resources management as a means for accounting for uncertainty, and to conduct a grey systems analysis of the tradeoffs between meeting water quantity/quality objectives and maximizing economic income in the specific case of Xiamen, China. The literature on water resource systems analysis was reviewed to arrive at an understanding of how water quantity and quality problems were analyzed and incorporated, how uncertainty was accounted for, and what cases have been studied in water quantity and quality management. The literature revealed that ( 1) previous studies of water quantity and quality management were related to river or lake basins, and none was about a canal basin with strict water quality requirements; (2) none of the studies in China combined both quantity and quality problems in an optimization framework; and (3) no previous study attempted to communicate uncertain messages directly into optimization processes and solutions. This study has developed a grey linear programming (GLP) model for water quantity allocation and quality planning, and advanced a new solving approach which can effectively incorporate uncertain messages into the optimization framework. This method has been applied to water quantity and quality management in a water delivery canal in Xiamen, China. Results of the case study indicate that the derived decision schemes are feasible for the study area. When the canal water quality has precedence, the scheme for lower limit of objective function has to be adopted. Under this alternative, less cropping area, manure application and livestock numbers, and no fertilizer application are programmed. When agricultural income has precedence, the scheme for upper limit of objective function can be adopted. Under this alternative, more cropping areas, manure application and livestock numbers, and some fertilizer application are programmed. Therefore, decision makers can adjust the grey decision variables (including cropping area, manure and ferti1izer applications and livestock numbers) within their grey intervals according to the detailed situations. Reliability of the method has been proved through sensitivity tests of the impacts of pollutant loss constraints on agricultural income, the costs of reducing pollutant losses, the impacts of water quantity constraints on agricultural income, and the effects of grey inputs on grey outputs

Rethinking lawns as prevalent elements of urban green spaces

The lawn is one of the most visible elements of urban green spaces and Western landscape styles. China has seen a dramatic increase in planted lawn areas. However, there is an urgent need for sustainable lawn alternatives (SLTs) in China due to serious threats to the urban environment from intensive lawn maintenance and cultural inadequacy of lawns. This thesis attempts to examine the reasons behind the historical context and current situation of lawns in China and offers suggestions for SLTs via a case study of Xi’an using transdisciplinary research framework from social-cultural and ecological perspectives. A historical study was performed on reasons of lawn development in Chinese cities and modern European and Chinese examples of lawn alternatives by reviewing literature and through field observation. Face-to-face interviews, questionnaires and observations were conducted to evaluate how stakeholders and park visitors perceive lawns and how this affects their decisions in designing, managing and using lawns and lawn alternatives. To identify how the design and management shape plant and pollinator diversity, biodiversity inventories were conducted. Finally, results from the three studies were analysed following a framework based on theories in landscape sustainability and ecosystem services. The results suggested that the Chinese people’s paradigm of lawns is influenced by westernisation and globalisation after the 1840s. Lawns evolve from changes in the relation-ship between humans and the environment. In classical Chinese gardens, groundcover species were used according to their ecological characteristics and suitability to site conditions. Lawns in Xi’an have the same core grass species as lawns used in geographically distant regions, contributing to lawn plant species homogenisation worldwide. Intensive maintenance negatively affected plant species diversity and native plant species, while in more planned green spaces, older and larger lawns harbour diverse plant species and native plant species. The aesthetic value and regulating services of lawns are mostly recognised by park visitors and stakeholders although lawns impair the provision of some regulating services for the intensive maintenance. Lawns fail to provide some culture services because of their limited accessibility and symbolism of Western culture. Pollination services can be provided if certain spontaneous native plant species are allowed to flower. Concrete suggestions for SLTs in China were proposed, although challenges that impinge the transition to SLTs were identified. Meanwhile, current social-cultural, environmental and economic conditions in China encourage their implementation. The thesis contributes to knowledge that addresses the mismatch between perceived and actual ecosystem services provided by lawns. The results can be used as references for design and management of SLTs in practice

Project MEDSAT: The design of a remote sensing platform for malaria research and control

Project MEDSAT was proposed with the specific goal of designing a satellite to remotely sense pertinent information useful in establishing strategies to control malaria. The 340 kg MEDSAT satellite is to be inserted into circular earth orbit aboard the Pegasus Air-Launched Space Booster at an inclination of 21 degrees and an altitude of 473 km. It is equipped with a synthetic aperture radar and a visible thermal/infrared sensor to remotely sense conditions at the target area of Chiapas, Mexico. The orbit is designed so that MEDSAT will pass over the target site twice each day. The data from each scan will be downlinked to Hawaii for processing, resulting in maps indicating areas of high malaria risk. These will be distributed to health officials at the target site. A relatively inexpensive launch by Pegasus and a design using mainly proven, off-the-shelf technology permit a low mission cost, while innovations in the satellite controls and the scientific instruments allow a fairly complex mission