Eike Steffen Reetz

Survey of Context Provisioning Middleware

In the scope of ubiquitous computing, one of the key issues is the awareness of context, which includes diverse aspects of the users situation including his activities, physical surroundings, location, emotions and social relations, device and network characteristics and their interaction with each other. This contextual knowledge is typically acquired from physical, virtual or logical sensors. To overcome problems of heterogeneity and hide complexity, a significant number of middleware approaches have been proposed for systematic and coherent access to manifold context parameters. These frameworks deal particularly with context representation, context management and reasoning, i.e. deriving abstract knowledge from raw sensor data. This article surveys not only related work in these three categories but also the required evaluation principles.

Effect of caching in a broker based context provisioning system

Caching is a well-established mechanism used in distributed systems for improving overall performance. In this paper, we analyse the effect of using a context cache in a broker-based context provisioning system. An experiment is carried out using a simulation based on our framework architecture of context consumers, context broker and context providers exchanging different types of context data over time. The results show notable improvement in the context query response time.

Towards global smart spaces: Merge Wireless Sensor Networks into context-aware systems

The integration of Wireless Sensor Networks at a global scale is a crucial step on the road to a tighter coupling between the virtual and real world. In a context-aware system with thousands or even millions of data items describing the current situation, it is obvious that this data needs to be filtered and aggregated in order to distribute the detection and processing efficiently. The need to aggregate data exists also from the perspective of the Wireless Sensor Network since energy is limited and there is a strong requirement to reduce communication traffic. Therefore, this paper illustrates the general concept of a context-aware system and explains in detail how to integrate Wireless Sensor Networks in such a system for global usage of information detected by numerous nodes. The concept is proven by implementation, measurements, and a theory of operation.

Test-Enabled Architecture for IoT Service Creation and Provisioning

The information generated from the Internet of Things (IoT) potentially enables a better understanding of the physical world for humans and supports creation of ambient intelligence for a wide range of applications in different domains. A semantics-enabled service layer is a promising approach to facilitate seamless access and management of the information from the large, distributed and heterogeneous sources. This paper presents the efforts of the IoT.est project towards developing a framework for service creation and testing in an IoT environment. The architecture design extends the existing IoT reference architecture and enables a test-driven, semantics-based management of the entire service lifecycle. The validation of the architecture is shown though a dynamic test case generation and execution scenario.

Performance evaluation of topologies for cooperative and Dynamic Resource Relaying

Relaying has been proposed to support users suffering from high shadowing or high interference and therefore being not able to receive high data rates. With adaptive relaying, a higher modulation and coding scheme (MCS) can be used which increases the feasible data rate. The investigation of relaying techniques widely concentrates on information theoretical methods. Instead, this paper focuses on system level simulations to exploit the achievable results within a realistic environment. The question which relaying methodology is the best choice if unicast and a multicast transmissions are possible is investigated. The results show that relaying techniques can improve the median cell throughput and decrease the outage probability in a mixed unicast and multicast environment. Cooperative relaying results in the lowest outage probability, whereas the introduced concept of dynamic resource relaying (DRR) offers a higher cell throughput. For the investigated LTE (3GPP long term evolution) system with a frequency re-use factor of one, the outage probability can be decreased by using relaying without further frequency planning.

Performance simulation of a context provisioning middleware based on empirical measurements

The evaluation of context middleware systems is a challenging endeavour. On the one hand, testbed investigations suffer from an unrealistic environment in terms of number of users, high implementation effort for changes and questionable portability of results. On the other hand simulation of middleware systems is complex due to the high abstraction of implementation. This article contributes to the understanding of a broker based context provisioning system based on black-box measurements of a testbed which are further utilised to increase the accuracy of a simulation model. Both simulations and measurements help in understanding the complex behaviour of a context provisioning middleware and enable the evaluation of complex distributed systems. The presented investigations identify significant parameters and corresponding models for the response delay of the key components of a context provisioning middleware and discuss their integration into an overall simulation model.

An artificial chemistry based framework for personal and social context aware smart spaces

Supporting context-aware services and applications that are delivered to a user as they move through a smart space is a challenge. The complexity of awareness and interaction requires an efficient interaction and adaptation model. Most research prototypes comprise of many models and extensive middleware which seems excessive for simple context-aware applications involving pervasive devices. Part of the problem is finding a conceptual abstraction which is compact and concise yet can exclusively model all the dynamism and expressivity required for such a system. In this paper we propose a context aware architecture based on a smart space context model and a middleware inspired by chemical reactions.

Agent based decision support system for optimizing logistical processes in agricultural production

The KOMOBAR project utilizes a software agent based approach to create a decision support system for the purpose of optimizing logistic processes in the agricultural domain. This domain requires a flexible approach, which has the ability to work decentralized. The paper explains an architecture for software agent based decentralised decision support structures and discusses the problems of mobile networks in rural areas. It points out possible solutions for a transparent multi-hop routing mechanism including store-carry-forward solutions. Furthermore, the paper outlines the usage of web-based technology to facilitate platform independent system components and a broad variety of client-side devices.

Automated Testing of Context-Aware Applications

The development of context-aware applications is a difficult and error-prone task. The dynamics of the environmental context combined with the complexity of the applications poses a vast number of possibilities for mistakes during the creation of new applications. Therefore it is important to test applications before they are deployed in a life system. For this reason, this paper proposes a testing tool, which will allow for automatic generation of various test cases from application description documents. Semantic annotations are used to create specific test data for context-aware applications. A test case reduction methodology based on test case diversity investigations ensures scalability of the proposed automated testing approach.

Performance evaluation of a context provisioning middleware

The evaluation of context middleware systems is a challenging endeavour. Testbed investigations suffer from an unrealistic environment in terms of number of users, high implementation effort for changes and questionable portability of results. Simulation of middleware systems is complex due to the high abstraction of implementation. This paper contributes towards the understanding of a broker based context provisioning system based on black-box measurements of a testbed which are further utilised to increase the accuracy of a simulation model. Both simulations and measurements help in understanding the complex behaviour of a context provisioning middleware and enable the evaluation of complex distributed systems. The presented investigations identify significant parameters and corresponding models for the response delay of the key components of a context provisioning middleware and discuss their integration into an overall simulation model.