Mats Neovius

A Formal Model of Context-Awareness and Context-Dependency

The communication environment surrounding our daily experience is increasingly characterized by mobile devices that can exchange multimedia information and provide access to various services of complex nature. The trend is now clear that future consumer computing experience would be based on multiple pervasive communication devices and services, where navigability, context-sensitivity, adaptability and ubiquity are key characteristics. Several issues have been studied, models and methodologies proposed, and tools and systems implemented. However, we look at the foundation, where some of the most relevant issues probably are a formal model of context-awareness and context-dependency. In this paper, we discuss a formal foundation and software engineering techniques for mobile context-aware and context-dependent service derivation and application development, emphasizing the relationships between context and system

Formal Modular Modelling of Context-Awareness

Characterising for a context-aware software is its ability to adjust to the prevailing situation. Such software reacts and bases the context-aware decisions upon inputs describing its operating conditions, i.e. on context(s). In this paper, we will seek the roots of context(s) and reason on the methods for deducing information by processing contexts; that is, present a methodology to enhance the relevance from raw data to knowledge. Thus, this paper will point out the relationship between introducing, constructing, serving, gluing and utilising context. Moreover, we show how to in a structured manner construct a context-service that satisfies given requirements and supplement the context-aware utiliser. For the sake of reuse and scalability, we will separate an applications specification from context reasoning and consider them as systems in their own rights. The findings will be motivated on a general level, with an easily conceivable example and formalised with the action system formalism.

A design framework for wireless sensor networks

Wireless sensor networks (sensornets) are wirelessly communicating smart gadgets with the capability of sensing the environment. With the immense applicability of sensornets, there is an increasing need of a general organisational and architectural development framework for sensomet systems. This paper outlines an abstract framework for modelling responsibilities and tasks to sets of nodes according to their vocation. These guidelines are presented with the intension to ease reasoning about a sensomet as a system, and its applications.

The Distance-Availability Weighted Piece Selection Method for BitTorrent: A BitTorrent Piece Selection Method for On-demand Streaming

During the last few years, BitTorrent has become a popular way of transferring large files over the Internet. However, the original out-of-order nature of the BitTorrent protocol has made it difficult to enable playback of media files which have not yet been fully transferred. In this paper we propose a new BitTorrent piece selection method to enable simultaneous playback of the transferred media file without impacting on the speed and quality of the transfer. Unlike the original rarest-first piece selection method, the distance-availability weighted method compromises between selecting rare pieces and pieces which are soon to be played back, making playback possible before the transfer is complete.

Formal transformation of platform independent models into platform specific models

This paper introduces a method for formal transformation of platform independent models (PIM) to platform specific models (PSM) in a model driven architecture (MDA) context. The models are constructed using state-machines in the Unified Modeling Language (UML). As a formal framework for reasoning about the models we use Event B. In this paper we illustrate our method by introducing fault tolerance to the PSM. Fault tolerance is not considered in the PIM in order to make the models reusable for different platforms. On the other hand, the PSM often has to consider platform specific faults. However, fault tolerance mechanisms cannot usually be introduced as a refinement in the PSM. We present a model transformation of the PIM in order to preserve refinement properties in the construction of the PSM. Design patterns are used for guiding the development. Our method can be beneficial for developing reliable applications in many different areas, since both UML and B are used for practical applications.

An abstract model for incentive-enhanced trust in p2p networks

Peer-to-Peer (P2P) networks have emerged as a prime research topic, partly due to the vast unexploited possibilities unrestricted distribution of the workload provides. The main hindrance for unrestricted exploitation of the P2P topology is, due to lack of security-related issues, the gullible attitude taken towards unknown agents. Therefore, the severity of the vulnerabilities caused by gullibility must be mended by other means, for example, by an effective incentive scheme encouraging agents to trustworthy behaviour. This paper presents an abstract model for incentive enhanced trust, to progressively assign the participating agents rights for accessing distributed resources, emphasising consistent behaviour. The model consists of a degrading formula, an illustrative incentive triangle and a best-effort distributed supervision model. Moreover, the same incentive model facilitates anticipation of future behaviour concerning any given agent founded on several distinct agents’ opinion, suggesting that any knowledge concerning the counterpart is better than none.

A Theory of Service Dependency

Service composition has become commonplace nowadays, in large part due to the increased complexity of software and supporting networks. Composition can be of many types, for instance sequential, prioritising, non-deterministic. However, a fundamental feature of the services to be composed consists in their dependencies with respect to each other. In this paper we propose a theory of service dependency, modelled around a dependency operator in the Action Systems formalism. We analyze its properties, composition behaviour, and refinement conditions with accompanying examples.

On Proving Recoverability of Smart Electrical Grids

Smart electrical grids refer to networked systems for distributing and transporting electricity from producers to consumers, by dynamically configuring the network through remotely controlled disconnectors. The consumers of the grid have typically distinct priorities, e.g., a hospital and an airport have the highest priority and the street lighting has a lower priority. This means that when electricity supply is compromised, e.g., during a storm, then the highest priority consumers should either not be affected or should be the first for whom electricity provision is recovered. In this paper, we propose a general formal model to study the provability of such a property. We have chosen Event-B as our formal framework due to its abstraction and refinement capabilities that support correct-by-construction stepwise development of models; also, Event-B is tool supported. Being able to prove various properties for such critical systems is fundamental nowadays, as our society is increasingly powered by dynamic digital solutions to traditional problems.

Forming a context‐sensitive web of trust by relying on sentimentally like‐minded

Purpose – Trust in open networks has emerged as a prime research topic, partly due to the vast unexploited possibilities unrestricted distribution of ideas, innovations and information provided. This paper aims to present an abstract model for anticipating the probabilities of the target object to meet with the expectations of the inquirer, emphasising consistent behaviour and managing diverse conceptions by relying on sentimentally like‐minded.Design/methodology/approach – The basic building blocks of trust are presented and motivated. Each presented problem is addressed and formulas facilitating rightful interpretation are given.Findings – The paper presents some ideas how to approach the problems faced when rightfully interpreting information gathered from anonymous collaborates in a scalable manner by pointing out the basics of them.Research limitations/implications – This paper depicts ideas as illustrations that are easy to understand and give an overview of the fundamentals on which to conduct furt...

Quantifying Uncertainty for Preemptive Resource Provisioning in the Cloud

To satisfy quality of service requirements in a cost-efficient manner, cloud service providers would benefit from providing a means for quantifying the level of operational uncertainty within their systems. This uncertainty arises due to the dynamic nature of the cloud. Since tasks requiring various amounts of resources may enter and leave the system at any time, systems plagued by high volatility are challenging in preemptive resource provisioning. In this paper, we present a general method based on Dempster-Shafer theory that enables quantifying the level of operational uncertainty in an entire cloud system or parts thereof. In addition to the standard quality metrics, we propose monitoring of system calls tocapture historical behavior of virtual machines as an input tothe general method. Knowing the level of operationaluncertainty enables greater accuracy in online resourceprovisioning by quantifying the volatility of thedeployedsystem