Abduction in Well-Founded Semantics and Generalized Stable Models

Abductive logic programming offers a formalism to declaratively express and solve problems in areas such as diagnosis, planning, belief revision and hypothetical reasoning. Tabled logic programming offers a computational mechanism that provides a level of declarativity superior to that of Prolog, and which has supported successful applications in fields such as parsing, program analysis, and model checking. In this paper we show how to use tabled logic programming to evaluate queries to abductive frameworks with integrity constraints when these frameworks contain both default and explicit negation. The result is the ability to compute abduction over well-founded semantics with explicit negation and answer sets. Our approach consists of a transformation and an evaluation method. The transformation adjoins to each objective literal $O$ in a program, an objective literal $not(O)$ along with rules that ensure that $not(O)$ will be true if and only if $O$ is false. We call the resulting program a {\em dual} program. The evaluation method, \wfsmeth, then operates on the dual program. \wfsmeth{} is sound and complete for evaluating queries to abductive frameworks whose entailment method is based on either the well-founded semantics with explicit negation, or on answer sets. Further, \wfsmeth{} is asymptotically as efficient as any known method for either class of problems. In addition, when abduction is not desired, \wfsmeth{} operating on a dual program provides a novel tabling method for evaluating queries to ground extended programs whose complexity and termination properties are similar to those of the best tabling methods for the well-founded semantics. A publicly available meta-interpreter has been developed for \wfsmeth{} using the XSB system.Comment: 48 pages; To appear in Theory and Practice in Logic Programmin

Every normal logic program has a 2-valued semantics: theory, extensions, applications, implementations

Trabalho apresentado no âmbito do Doutoramento em Informática, como requisito parcial para obtenção do grau de Doutor em InformáticaAfter a very brief introduction to the general subject of Knowledge Representation and Reasoning with Logic Programs we analyse the syntactic structure of a logic program and how it can influence the semantics. We outline the important properties of a 2-valued semantics for Normal Logic Programs, proceed to define the new Minimal Hypotheses semantics with those properties and explore how it can be used to benefit some knowledge representation and reasoning mechanisms. The main original contributions of this work, whose connections will be detailed in the sequel, are: • The Layering for generic graphs which we then apply to NLPs yielding the Rule Layering and Atom Layering — a generalization of the stratification notion; • The Full shifting transformation of Disjunctive Logic Programs into (highly nonstratified)NLPs; • The Layer Support — a generalization of the classical notion of support; • The Brave Relevance and Brave Cautious Monotony properties of a 2-valued semantics; • The notions of Relevant Partial Knowledge Answer to a Query and Locally Consistent Relevant Partial Knowledge Answer to a Query; • The Layer-Decomposable Semantics family — the family of semantics that reflect the above mentioned Layerings; • The Approved Models argumentation approach to semantics; • The Minimal Hypotheses 2-valued semantics for NLP — a member of the Layer-Decomposable Semantics family rooted on a minimization of positive hypotheses assumption approach; • The definition and implementation of the Answer Completion mechanism in XSB Prolog — an essential component to ensure XSB’s WAM full compliance with the Well-Founded Semantics; • The definition of the Inspection Points mechanism for Abductive Logic Programs;• An implementation of the Inspection Points workings within the Abdual system [21] We recommend reading the chapters in this thesis in the sequence they appear. However, if the reader is not interested in all the subjects, or is more keen on some topics rather than others, we provide alternative reading paths as shown below. 1-2-3-4-5-6-7-8-9-12 Definition of the Layer-Decomposable Semantics family and the Minimal Hypotheses semantics (1 and 2 are optional) 3-6-7-8-10-11-12 All main contributions – assumes the reader is familiarized with logic programming topics 3-4-5-10-11-12 Focus on abductive reasoning and applications.FCT-MCTES (Fundação para a Ciência e Tecnologia do Ministério da Ciência,Tecnologia e Ensino Superior)- (no. SFRH/BD/28761/2006

Distributed Abductive Reasoning: Theory, Implementation and Application

Abductive reasoning is a powerful logic inference mechanism that allows assumptions to be made during answer computation for a query, and thus is suitable for reasoning over incomplete knowledge. Multi-agent hypothetical reasoning is the application of abduction in a distributed setting, where each computational agent has its local knowledge representing partial world and the union of all agents' knowledge is still incomplete. It is different from simple distributed query processing because the assumptions made by the agents must also be consistent with global constraints. Multi-agent hypothetical reasoning has many potential applications, such as collaborative planning and scheduling, distributed diagnosis and cognitive perception. Many of these applications require the representation of arithmetic constraints in their problem specifications as well as constraint satisfaction support during the computation. In addition, some applications may have confidentiality concerns as restrictions on the information that can be exchanged between the agents during their collaboration. Although a limited number of distributed abductive systems have been developed, none of them is generic enough to support the above requirements. In this thesis we develop, in the spirit of Logic Programming, a generic and extensible distributed abductive system that has the potential to target a wide range of distributed problem solving applications. The underlying distributed inference algorithm incorporates constraint satisfaction and allows non-ground conditional answers to be computed. Its soundness and completeness have been proved. The algorithm is customisable in that different inference and coordination strategies (such as goal selection and agent selection strategies) can be adopted while maintaining correctness. A customisation that supports confidentiality during problem solving has been developed, and is used in application domains such as distributed security policy analysis. Finally, for evaluation purposes, a flexible experimental environment has been built for automatically generating different classes of distributed abductive constraint logic programs. This environment has been used to conduct empirical investigation of the performance of the customised system

The CIFF Proof Procedure for Abductive Logic Programming with Constraints: Definition, Implementation and a Web Application

Abduction has found broad application as a powerful tool for hypothetical reasoning with incomplete knowledge, which can be handled by labeling some pieces of information as abducibles, i.e. as possible hypotheses that can be assumed to hold, provided that they are consistent with the given knowledge base. Attempts to make the abductive reasoning an effective computational tool gave rise to Abductive Logic Programming (ALP) which combines abduction with standard logic programming. A number of so-called proof procedures for ALP have been proposed in the literature, e.g. the IFF procedure, the Kakas and Mancarella procedure and the SLDNFA procedure, which rely upon extensions of different semantics for logic programming. ALP has also been integrated with Constraint Logic Programming (CLP), in order to combine abductive reasoning with an arithmetic tool for constraint solving. In recent years, many proof procedures for abductive logic programming with constraints have been proposed, including ACLP and the A-System which have been applied to many fields, e.g. multi-agent systems, scheduling, integration of information. This dissertation describes the development of a new abductive proof procedure with constraints, namely the CIFF proof procedure. The description is both at the theoretical level, giving a formal definition and a soundness result with respect to the three-valued completion semantics, and at the implementative level with the implemented CIFF System 4.0 as a Prolog meta-interpreter. The main contributions of the CIFF proof procedure are the advances in the expressiveness of the framework with respect to other frameworks for abductive logic programming with constraints, and the overall computational performances of the implemented system. The second part of the dissertation presents a novel application of the CIFF proof procedure as the computational engine of a tool, the CIFFWEB system, for checking and (possibly) repairing faulty web sites. Indeed, the exponential growth of the WWW raises the question of maintaining and automatically repairing web sites, in particular when the designers of these sites require them to exhibit certain properties at both structural and data level. The capability of maintaining and repairing web sites is also important to ensure the success of the Semantic Web vision. As the Semantic Web relies upon the definition and the maintenance of consistent data schemas (XML/XMLSchema, RDF/RDFSchema, OWL and so on), tools for reasoning over such schemas (and possibly extending the reasoning to multiple web pages) show great promise. The CIFFWEB system is such a tool which allows to verify and to repair XML web sites instances, against sets of requirements which have to be fulfilled, through abductive reasoning. We define an expressive characterization of rules for checking and repairing web sites' errors and we do a formal mapping of a fragment of a well known XML query language, namely Xcerpt, to abductive logic programs suitable to fed as input to the CIFF proof procedure. Finally, the CIFF proof procedure detects the errors and possibly suggests modifications to the XML instances to repair them. The soundness of this process is directly inherited from the soundness of CIFF

Fresh Perspectives on the 'War on Terror'

On 20 September 2001, in an address to a Joint Session of Congress and the American people, President George W Bush declared a ‘war on terror’. The concept of the ‘war on terror’ has proven to be both an attractive and a potent rhetorical device. It has been adopted and elaborated upon by political leaders around the world, particularly in the context of military action in Afghanistan and Iraq. But use of the rhetoric has not been confined to the military context. The ‘war on terror’ is a domestic one, also, and the phrase has been used to account for broad criminal legislation, sweeping agency powers and potential human rights abuses throughout much of the world. This collection seeks both to draw on and to engage critically with the metaphor of war in the context of terrorism. It brings together a group of experts from Australia, Canada, the United Kingdom, France and Germany who write about terrorism from a variety of disciplinary perspectives including international law and international relations, public and constitutional law, criminal law and criminology, legal theory, and psychology and law

Defying Victimhood: Women and Post-Conflict Peacebuilding

The chapters in this volume cover a wide range of women’s post-conflict peacebuilding experiences in different parts of the world. Post-conflict situations are windows of opportunity during which gender relations can and should be rethought and which, if properly utilized, can serve as the right moment to “rewrite” the rules and practices that previously served as obstacles to the participation of women in society. Overall, our book is meant to challenge the popular and often-propagated assumption that women should be supported, empowered and given a voice merely in their roles as victims. Collectively, we provide evidence in support of the growing understanding at international, national and local levels that while – and because – women are disproportionately affected by war, they can be powerful agents of positive and sustainable change if brought on board and given the chance to participate in every aspect of a society’s peacebuilding process

Controlling the circulation of small arms in international law

International humanitarian law (IHL) and international human rights law (IHRL) have shown an influence on the conventional arms control. A series of negotiations to control the trade of small arms, in particular the diplomatic conference on the arms trade treaty in July 2012, provide some evidence of this increasing influence. The negative impact of the widespread availability of small arms on human security justifies the linking of the use of these weapons with humanitarian and human rights law. The Security Council arms embargo, a reactive sanction measure imposed retrospectively, the only legal mechanism restricting small arms transfers, is often ineffective in achieving its objective. What is required is preventive action. Other international mechanisms, such as the 2001 United Nations Programme of Action on small arms, the UN Register, and the 2005 International Tracing Instrument cannot be implemented effectively for several reasons, in particular, because they are not legally binding instruments. The contemporary principle of State responsibility obliges States to regulate the small arms trade in the interest of preventing violence and ensuring security of all peoples. This obligation extends to those within and beyond their boundaries, in other words to the global population as a whole. Therefore, a selling State should not transfer weapons to another State if it is aware that the weapons may be used by the receiving State for internationally wrongful acts which would constitute a violation of international law. States have a responsibility to act in accordance with international norms of human rights and humanitarian law. Hence, a small arms transfer to another State, including for the purpose of self-defence, should be compatible with the requirements of IHL and IHRL. An examination of the treaties regarding conventional weapons from the 1868 St Petersburg Declaration to the 2008 Convention on Cluster Munitions shows the increasing reference to principles of humanitarian law and human rights law. Their influence is also evident in the regional and sub-regional instruments. The recent adoption of the Mine Ban Convention and the Convention on Cluster Munitions was finalised outside the United Nations with a wide participation of civil society which promotes respect for human rights. This suggests that a future arms control negotiation may have to take into consideration human rights and humanitarian concerns, and can be pursued outside the United Nations framework

Kenya’s changing counterterrorism policy: From the unsecuritization to the securitization of terrorism

This study investigates why Kenya, unlike other states around the world, did not enact anti-terrorism legislation that would have enabled it to have counterterrorism measures in the aftermath of 9/11 and only did so in 2012. Previous studies argue that concerns about the negative effects of anti-terrorism laws on Kenya’s nascent democratic system and its civil liberties were the main reasons why Kenya’s government could not enact proposed anti-terrorism legislation in 2003 and 2006. However, these studies do not explain why those who had previously opposed anti-terrorism legislation supported the enactment of an anti-terrorism law in 2012 even though their views about the importance of civil liberties and democracy had not changed. Similarly, previous studies which suggest that Kenya enacted anti-terrorism legislation in 2012 because of the detrimental effects of terrorism on the country’s security and economic interests do not explain why these factors did not elicit the same response in 2003 and 2006. Departing from previous studies, this research hypothesises that Kenya’s enactment of counterterrorism measures was dependent on consensus building among the country’s executive and legislative arms of government. To test this hypothesis, this thesis proposed six contextual factors that were used to explain how and why perceptions about the terrorism threat in Kenya developed and changed. Two methods, discourse analysis and process tracing, were used to establish the relationships between the variables in this study. In this regard, discourse analysis provided rich descriptions of the construction and evolution of the terrorist threat in Kenya. The rich descriptions were initially derived from written texts including the Kenya National Assembly Hansard, policy documents, court documents and public testimonies. The data was then triangulated with descriptions obtained from spoken texts including semi-structured interviews, archival press conferences and media recordings. The recurring linguistic patterns obtained from these descriptions formed the narratives that explained how Kenya’s government framed terrorism and the impact that this had on the enactment of anti-terrorism legislation. Process tracing supplemented discourse analysis by pinpointing the conditions under which the securitization of terrorism occurred. In addition to unravelling Kenya’s puzzling counterterrorism behaviour, this thesis contributes to knowledge in two ways. First, it identifies and expounds on new variables that explain Kenya’s puzzling counterterrorism behaviour. Second, this thesis extends literature in securitization studies by explaining how contextual factors can be used to understand both unsecuritization and securitization processes

On 'a continuum with expansion' : UK-US intelligence relations & wider reflections on international intelligence liaison

Since 9/11, intelligence liaison has increased exponentially. Yet, both in international affairs and within the academic fields of international relations (IR) and intelligence studies, the phenomenon of intelligence liaison remains under-researched and under-theorised. Moreover, intelligence studies remain remarkably disconnected from IR. Accordingly, this study attempts to advance a timely understanding of both international intelligence liaison generally, and UK-US intelligence liaison specifically, in a contemporary context. Methodologically, this is accomplished through conducting a qualitative analysis of UK-US intelligence liaison focussed on two ‘critical’ and ‘intensive’ case studies. These represent the key issues over which the UK and US have liaised, namely counter-terrorism and weapons of mass destruction (WMD) non-/counter-proliferation. In practical terms, the ‘rise’ of intelligence liaison can be substantially explained. However, the phenomenon itself can only be ‘theorised’ so far. Intelligence is, by its very nature, a fragmented subject. Accordingly, cascades of complexities increasingly enter, especially at the lower/micro levels of analysis - where the details and specifics concerning particular sources and operations matter further. Therefore, intelligence liaison effectively represents the concept of ‘complex co-existence plurality’ in action. This is both at and across all its different, yet closely interrelated, levels of analysis, and also when broken down into eight systemic variables or attributes. Notwithstanding this complexity, wider conclusions can be drawn, allowing this thesis to advance the proposition that we are now witnessing the globalisation of intelligence. Overall, this trend is facilitated through the developments occurring in a web of overlapping international intelligence liaison arrangements, which collectively span the globe. Reflective of a continuously evolving attempt for ‘optimum outreach’, these intraliaison developments include: firstly, the establishing of frameworks and defining of operational parameters for the intelligence liaison arrangements, and then their subsequent consolidation (or normalisation) and optimisation over time. These wider trends are simultaneously observable in the microcosm of UK-US intelligence liaison relations, which are also on ‘a continuum with expansion’ as the UK and US remain broadly exemplary ‘friends and allies’