Explicitly Context-Aware Publish/Subscribe with Context-Invariant Subscriptions

Although context could be exploited to improve the performance, elasticity and adaptation in most distributed systems that adopt the publish/subscribe (P/S) model of communication, only very few works have explored domains with highly dynamic context, whereas most adopted models are context agnostic. In this paper, we present the key design principles underlying a novel context-aware content-based P/S (CA-CBPS) model of communication, where the context is explicitly managed, focusing on the minimization of network overhead in domains with recurrent context changes thanks to contextual scoping. We highlight how we dealt with the main shortcomings of most of the current approaches. Our research is some of the first to study the problem of explicitly introducing context-awareness into the P/S model to capitalize on contextual information. The envisioned CA-CBPS middleware enables the cloud ecosystem of services to communicate very efficiently, in a decoupled, but contextually scoped fashion

Efficient State Update Exchange in a CPS Environment for Linked Data-based Digital Twins

International audienceThis paper addresses the problem of reducing the number of messages needed to exchange state updates between the Cyber-Physical System (CPS) components that integrate with the rest of the CPS through Digital Twins in order to maintain uniform communication interface and carry out their tasks correctly and safely. The main contribution is a proposed architecture and the discussion of its suitability to support correct execution of complex tasks across the CPS. A new State Event Filtering component is presented to provide event-based communication among Digital Twins that are based on the Linked Data principles while keeping the fan-out limited to ensure the scalability of the architecture

Context-Aware Publish Subscribe in Mobile ad Hoc Networks

The publish-subscribe communication paradigm is enjoying increasing popularity thanks to its ability to simplify the development of complex distributed applications. However, existing solutions in the publish-subscribe domain address only part of the challenges associated with the development of applications in dynamic scenarios such as mobile ad hoc networks. Mobile applications must be able to assist users in a variety of situations, responding not only to their inputs but also to the characteristics of the environment in which they operate. In this paper, we address these challenges by extending the publish-subscribe paradigm with the ability to manage and exploit context information when matching events against subscriptions. We present our extension in terms of a formal model of context-aware publish-subscribe. We propose a solution for its implementation in MANETs; and finally we validate our approach by means of extensive simulations

Mobile Spatial Subscriptions for Location-Aware Services

Spatial subscriptions have been used to specify locations of interest in Distributed Event-based Systems (DEBSs). However, current DEBSs representations to support spatial subscriptions are not expressive enough to describe some forms of subscriptions in mobile settings. For instance, users are not allowed to specify a spatial subscription that refers to other more well-known locations, in case they are not familiar with the names of their current locations. In addition, the middleware in existing DEBSs does not support changes at runtime, and modification to these middleware systems to support spatial subscriptions are highly coupled with specific DEBS infrastructures. In this thesis, I argue that by enhancing the expressiveness of spatial subscriptions, a new model of mobile spatial subscriptions for location-aware services can be defined and a reusable plug-in implementation approach that supports existing DEBSs can be developed. This thesis first summarizes the essential abstractions to specify mobile spatial subscriptions, and analyze the expressiveness of existing DEBSs to support these abstractions. Second, it proposes a three-level mobile spatial subscription model, which supports the essential abstractions used to specify spatial subscriptions. The first level of the model handles subscriptions consisting of geometric coordinates; the second level supports subscriptions with location labels; the third level interprets subscriptions which specify locations by stating their dynamic properties. Next, a plug-in implementation approach is introduced, and hence, the three-level model can be integrated with different DEBSs with minimal modification to the middleware. The subscription model is implemented as a subscriber/publisher component, instead of directly modifying the existing DEBS. Finally, I develop a prototype system, Dynamic Mobile Subscription System (DMSS), and illustrate the usefulness and applicability of the three-level model and the plug-in implementation approach

On Introducing Location Awareness in Publish-Subscribe Middleware

Having the possibility of routing messages only toward specific areas or subscribing to messages originating in specific locations seems natural when a publish-subscribe model of communication is adopted. Unfortunately, very few work have investigated such kind of services and none of the most widely adopted publish-subscribe middleware implements them. In this paper we first classify possible location-based publish-subscribe services, then we describe an algorithm to efficiently implement them in a distributed publish-subscribe middleware.

On Introducing Location Awareness in Publish-Subscribe Middleware

Having the possibility of routing messages only toward specific areas or subscribing to messages originating in specific locations seems natural when a publish-subscribe model of communication is adopted. Unfortunately, very few work have investigated such kind of services and none of the most widely adopted publish-subscribe middleware implements them. In this paper we first classify possible location-based publish-subscribe services, then we describe an algorithm to efficiently implement them in a distributed publish-subscribe middleware

Disseminação de dados em redes de sensores

Tese de mestrado, Engenharia Informática (Arquitectura, Sistemas e Redes de Computadores), Universidade de Lisboa, Faculdade de Ciências, 2010As redes de sensores sem fios (RSSF) são compostas por um grande número de pequenos dispositivos que monitorizam o ambiente em que estão inseridas. Estes dispositivos são caracterizados pelas restrições a nível energético, poder de processamento e de memória. As fortes restrições a que os dispositivos estão sujeitos obrigam à utilização de paradigmas de comunicação específicos, que tenham em consideração uma utilização racional dos recursos. Com a especialização dos nós receptores surge a necessidade destes conseguirem expressar o interesse em informação que considerem relevante, independentemente dos restantes participantes. O paradigma de comunicação usado tipicamente nas RSSF não considera os interesses que os nós receptores têm na informação que está a ser transmitida, pelo que pode ser enviado um grande número de mensagens nas quais nenhum nó receptor está interessado. O envio de mensagens desnecessárias é particularmente penalizador nas RSSF, uma vez que a actividade do rádio é responsável pelo consumo de grande parte da energia que os dispositivos dispõem. Sendo a memória um recurso escasso, importa também que o paradigma de comunicação seja igualmente eficiente em termos da quantidade de memória utilizada. Este trabalho apresenta e avalia experimentalmente um sistema Publicador/Subscritor que tem em conta o interesse dos nós em determinados tipos de informação e suprime o envio de informação sem relevância. Para além disso, o sistema adapta-se às restrições de energia e de memória dos dispositivos. Adicionalmente é apresentada uma concretização dum algoritmo de disseminação para o sistema operativo TinyOS que sugere que o sistema apresentado é exequível em sensores reais.Wireless sensor networks (WSN) are composed of a large number of small devices which monitor the environment in which they operate. These devices are characterized by restrictions like energy, processing and memory. The strong restrictions on the devices enforce the use of paradigms of communication which take into account a rational use of resources. With the specialization of the receptor nodes arises the need for them to be able express interest in information they deem relevant, regardless the interests of other participants. The paradigm of communication typically used in WSNs does not consider the receivers’ interests in information being transmitted, so it is possible to send a large number of messages in which no receiver node is interested. Sending unnecessary messages is particularly expensive in WSNs, since the activity of the radio is responsible for consuming much of the power the devices have. Since memory is a scarce resource, the paradigm of communication must also be efficient in the amount of memory used. This work presents and experimentally evaluates a Publisher/Subscriber system which takes into account the interest of the nodes in certain types of information and suppresses the sending of information without relevance. In addition, the system adapts to the resource constraints of devices such as reduced energy capacity and scarce memory space. Additionally, an implementation of an dissemination algorithm to the TinyOS operating system is presented. This implementation suggests that the presented system is feasible in real sensors

The influences of the just-in-time social cloud on real world decisions

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 209-224).People have intertemporal biases towards choices that result in immediate gratification versus delayed rewards. The social context can accentuate or downplay preferences towards virtues or vices when making choices in the moment. Especially in our modern world where social networks are virtually accessible at anytime, from anywhere, how our day-today decisions are affected by the "always-on" connection to our social networks via mobile devices is an open question. By understanding the dimensions of these social forces, we can utilize the just-in-time social cloud to nudge people towards decisions that have long term benefits for health and finances, while counterbalancing the forces of the marketers that trigger our impulses towards immediate temptations that we may regret later. This work presents an empirical inquiry into the effect of just-in-time social influences in human decision-making. In order to understand these effects and discover their parameters, I design and deploy real-world experiments with the just-in-time social cloud using mobile phones as platforms for just-in-time social influence. The Open Transaction Network forms the basis of generating just-in-time social networks based on the transactions shared by people in the context of commerce. The Open Transaction Network is extended to several systems to conduct real-world experiments involving real choices. By augmenting mobile commerce applications with just-in-time social networks, I design a mobile commerce environment that can socially influence our just-in-time choices. The Open Credit Card Application Framework augments existing methods of payment by using transactions as triggers to enable mobile applications that facilitate just-in-time decisions or reflections. Friends within communities show significant similarity in their hourly transaction behaviors. Varying manifestations of the just-in-time social cloud (individual friends, groups of friends and popularity information) can be used to nudge people's choices in the dimensions of taste, price and time as they decide.by Kwan Hong Lee.Ph.D

Protocols for the efficient dissemination of context-aware messages

Context-aware applications are able to react and adapt to the context of their users. This context includes, for instance, location, properties of the user or their surroundings, nearby devices, etc. Over the last years, powerful mobile devices, i.e., smartphones or tablet computers, have become an important part in many people's computing life. Most of these devices maintain a continuous high-speed network connection, allowing to provide distributed applications with an uninterrupted stream of data. Additionally, a huge number of sensors, both in these mobile devices and deployed in our surroundings, enable the creation of comprehensive context models. Such large-scale context models open up new possibilities for the development of context-aware applications by providing access to relevant context information from providers all over the world. However, until now, applications need to query the context model for relevant information or register for events or messages; it is not possible to "push" information to the mobile devices, neither from the infrastructure nor from other mobile devices. To support application developers, we propose Contextcast, a novel communication paradigm that allows for the dissemination of context-aware (or contextual) messages in a system of context-aware routers. This includes the fundamental semantics to address clients using context constraints and a reference dissemination scheme for such messages. To enable Contextcast to grow to scales similar to the context-aware systems that it is intended to be used with, we also propose a couple of optimized routing approaches. They are designed to reduce the number of maintenance messages that are necessary for the dissemination of contextual messages. One optimized routing algorithm uses coarse context information to reduce the amount of context updates propagated to routers. To this end, routers use the similarity of contexts to automatically find groups of similar clients, whose information can then be propagated as a single, coarse context. While this reduces the amount of context information to be propagated, the resulting information loss causes more messages to be forwarded, since routers no longer possess exact information to match against the constraints in contextual messages. A configurable similarity threshold allows for various trade-offs between the coarseness of the context information and the resulting additional message load. The second orthogonal routing approach relies on statistics to determine the characteristics of contexts and messages in the system. Without context knowledge, routers must assume the presence of a matching recipient and forward a message speculatively to disseminate it to all recipients. Using statistics, routers can determine how often certain messages occur and then calculate the benefit of propagating contexts corresponding to these messages. Several parameters enable an administrator to adjust how fast the system reacts to changes, depending on the observed messages and context updates. Additionally, temporal support extends Contextcast with a powerful mechanism that allows application developers and clients to address messages to certain contexts in the past or future. This includes an additional context attribute \cattr{time} and a constraint with various, easy to use temporal operators. We also propose efficient routing approaches for historical and future messages. Routing historical messages focuses on efficient routing while effectively protecting the clients' privacy, i.e., their respective context history. The routing approach for future messages delays forwarding messages until a matching context is registered, thus preventing needlessly forwarded messages