Distributed Approximation of Fixed-Points in Trust Structures

Recently, Carbone, Nielsen and Sassone introduced the trust-structure framework; a semantic model for trust-management in global-scale distributed systems. The framework is based on the notion of trust structures; a set of ``trust-levels'' ordered by two distinct partial orderings. In the model, a unique global trust-state is defined as the least fixed-point of a collection of local policies assigning trust-levels to the entities of the system. However, the framework is a purely denotational model: it gives precise meaning to the global trust-state of a system, but without specifying a way to compute this abstract mathematical object. This paper complements q the denotational model of trust structures with operational techniques. It is shown how the least fixed-point can be computed using a simple, totally-asynchronous distributed algorithm. Two efficient protocols for approximating the least fixed-point are provided, enabling sound reasoning about the global trust-state without computing the exact fixed-point. Finally, dynamic algorithms are presented for safe reuse of information between computations, in face of dynamic trust-policy updates

IMPORTANCE OF CAP REFORMS FOR THE DUTCH AGRICULTURAL SECTOR IN 2000-2020

Since 2000, the two important reforms of The EU Common Agricultural Policy (CAP) took place. The Agenda 2000 Berlin Agreement of March 1999 aimed to increase EU agriculture market orientation and focuses on the grain, oilseed, dairy and the beef sectors. It reduced intervention prices in these sectors and lowered the set-aside requirements for crops and by implementation of non-crop specific compensatory payments. The core of The Luxembourg Agreement from June 2003 was an acceleration of decoupling of farm support initiated by the Agenda 2000 complementary payment. It introduces a system of direct payments (known as single payment scheme - SPS), which are no longer linked to the production (decoupling). This CAP reform also includes commodity specific measures, especially in dairy sector. The Luxemburg Agreement links the direct payments to farmers with farm management practices which maintain environmental and other requirements set at EU and national levels (‘Cross-compliance’). The goal of this paper is twofold. First, we investigate the impact of the CAP reform on the Dutch agricultural sector in 2004 – 2007; second we examine effects of possible future CAP reform decision on the Dutch agriculture till 2020. The study is based on the AGMEMOD econometric model developed within the framework of projects financed by the European Commission. It reflects a sectoral, dynamic, partial equilibrium model, which takes into account the national specificities and is built up of models for the Member States of the EU27. The foundation for AGMEMOD is laid in the establishment of country model templates, which must achieve compatibility of the models to be built and the communality of data. The most important differences between the national models are macroeconomic assumptions, components of policies under the CAP and SAPS (in respect with the new Member States) and assumptions on the impact of direct payments on agricultural production (degree of decoupling). On the country level, commodity templates must encapsulate the modeling system to be used. Many components of these templates are based on the information and guidelines delivered by Hanrahan (2001), but then adapted to country-specific conditions. At least, they must contain issues on market and policy description, flow charts, key market and specification of the functional forms of the commodity model. The AGMEMOD model covers all important CAP commodities: grains, oilseeds, potatoes, sugar and sugar beets, livestock products, milk and dairy products. We will investigate the CAP impact on the Dutch agriculture by mean of policy simulations with the Dutch AGMEMOD model. To isolate policy effect in the historical period 2000 - 2007, counterfactual simulations for 2000 - 2007 will be run. To simulate the response of the Dutch agriculture on different policy changes in 2008 - 2020, the no-policy change baseline scenario will be developed and several policy experiments will be conducted: milk quota abolition, biofuel directive implementation and animal premiums decoupling. To indentify the policy effects the policy scenarios will be compared with the baseline.CAP, CAP Reform, Dutch agriculture, Agricultural and Food Policy, Research Methods/ Statistical Methods, Q10, Q18,

A Formal Framework for Concrete Reputation Systems

In a reputation-based trust-management system, agents maintain information about the past behaviour of other agents. This information is used to guide future trust-based decisions about interaction. However, while trust management is a component in security decision-making, many existing reputation-based trust-management systems provide no formal security-guarantees. In this extended abstract, we describe a mathematical framework for a class of simple reputation-based systems. In these systems, decisions about interaction are taken based on policies that are exact requirements on agents’ past histories. We present a basic declarative language, based on pure-past linear temporal logic, intended for writing simple policies. While the basic language is reasonably expressive (encoding e.g. Chinese Wall policies) we show how one can extend it with quantification and parameterized events. This allows us to encode other policies known from the literature, e.g., ‘one-out-of-k’. The problem of checking a history with respect to a policy is efficient for the basic language, and tractable for the quantified language when policies do not have too many variables

Markov Decision Processes with Applications in Wireless Sensor Networks: A Survey

Wireless sensor networks (WSNs) consist of autonomous and resource-limited devices. The devices cooperate to monitor one or more physical phenomena within an area of interest. WSNs operate as stochastic systems because of randomness in the monitored environments. For long service time and low maintenance cost, WSNs require adaptive and robust methods to address data exchange, topology formulation, resource and power optimization, sensing coverage and object detection, and security challenges. In these problems, sensor nodes are to make optimized decisions from a set of accessible strategies to achieve design goals. This survey reviews numerous applications of the Markov decision process (MDP) framework, a powerful decision-making tool to develop adaptive algorithms and protocols for WSNs. Furthermore, various solution methods are discussed and compared to serve as a guide for using MDPs in WSNs

A Formal Model for Trust in Dynamic Networks

We propose a formal model of trust informed by the Global Computing scenario and focusing on the aspects of trust formation, evolution, and propagation. The model is based on a novel notion of trust structures which, building on concepts from trust management and domain theory, feature at the same time a trust and an information partial order

Cross-layer design of multi-hop wireless networks

MULTI -hop wireless networks are usually defined as a collection of nodes equipped with radio transmitters, which not only have the capability to communicate each other in a multi-hop fashion, but also to route each others’ data packets. The distributed nature of such networks makes them suitable for a variety of applications where there are no assumed reliable central entities, or controllers, and may significantly improve the scalability issues of conventional single-hop wireless networks. This Ph.D. dissertation mainly investigates two aspects of the research issues related to the efficient multi-hop wireless networks design, namely: (a) network protocols and (b) network management, both in cross-layer design paradigms to ensure the notion of service quality, such as quality of service (QoS) in wireless mesh networks (WMNs) for backhaul applications and quality of information (QoI) in wireless sensor networks (WSNs) for sensing tasks. Throughout the presentation of this Ph.D. dissertation, different network settings are used as illustrative examples, however the proposed algorithms, methodologies, protocols, and models are not restricted in the considered networks, but rather have wide applicability. First, this dissertation proposes a cross-layer design framework integrating a distributed proportional-fair scheduler and a QoS routing algorithm, while using WMNs as an illustrative example. The proposed approach has significant performance gain compared with other network protocols. Second, this dissertation proposes a generic admission control methodology for any packet network, wired and wireless, by modeling the network as a black box, and using a generic mathematical 0. Abstract 3 function and Taylor expansion to capture the admission impact. Third, this dissertation further enhances the previous designs by proposing a negotiation process, to bridge the applications’ service quality demands and the resource management, while using WSNs as an illustrative example. This approach allows the negotiation among different service classes and WSN resource allocations to reach the optimal operational status. Finally, the guarantees of the service quality are extended to the environment of multiple, disconnected, mobile subnetworks, where the question of how to maintain communications using dynamically controlled, unmanned data ferries is investigated

Introducing Dynamic Behavior in Amalgamated Knowledge Bases

The problem of integrating knowledge from multiple and heterogeneous sources is a fundamental issue in current information systems. In order to cope with this problem, the concept of mediator has been introduced as a software component providing intermediate services, linking data resources and application programs, and making transparent the heterogeneity of the underlying systems. In designing a mediator architecture, we believe that an important aspect is the definition of a formal framework by which one is able to model integration according to a declarative style. To this purpose, the use of a logical approach seems very promising. Another important aspect is the ability to model both static integration aspects, concerning query execution, and dynamic ones, concerning data updates and their propagation among the various data sources. Unfortunately, as far as we know, no formal proposals for logically modeling mediator architectures both from a static and dynamic point of view have already been developed. In this paper, we extend the framework for amalgamated knowledge bases, presented by Subrahmanian, to deal with dynamic aspects. The language we propose is based on the Active U-Datalog language, and extends it with annotated logic and amalgamation concepts. We model the sources of information and the mediator (also called supervisor) as Active U-Datalog deductive databases, thus modeling queries, transactions, and active rules, interpreted according to the PARK semantics. By using active rules, the system can efficiently perform update propagation among different databases. The result is a logical environment, integrating active and deductive rules, to perform queries and update propagation in an heterogeneous mediated framework.Comment: Other Keywords: Deductive databases; Heterogeneous databases; Active rules; Update