Roland Reichle

A comprehensive context modeling framework for pervasive computing systems

Context management in pervasive computing environments must reflect the specific characteristics of these environments, e.g. distribution, mobility, resource-constrained devices, or heterogeneity of context sources. Although a number of context models have been presented in the literature, none of them supports all of these requirements to a sufficient extent at the same time. In this paper, we present a comprehensive and integrated approach for context modeling in pervasive computing environments. It combines the advantages of existing approaches and addresses the need for supporting effective software development. The proposed context model follows an ontology-based approach and has three layers of abstraction, i.e. conceptual layer, exchange layer, and functional layer. This layered approach facilitates a model-driven development of context-aware applications. Throughout the paper we compare our solution with the related work in order to clearly demonstrate why we needed to develop a new context management framework and where we have adopted existing ideas.

A Context Query Language for Pervasive Computing Environments

This paper identifies requirements for querying and accessing context information in mobile and pervasive computing environments. Furthermore it studies existing query languages showing that they satisfy only a subset of these requirements or cover some of them only to a limited extent. A new context query language is presented to overcome these shortcomings, improving the state of the art in several respects: heterogeneous representations of context information, definition of complex filtering mechanisms, elaborate aggregation functions and ontology integration, all in one language.

Modeling of Context-Aware Self-Adaptive Applications in Ubiquitous and Service-Oriented Environments

Mobile computing in ubiquitous environments has to cope with both predictable and unpredictable changes in the execution context, which introduces the need for context-aware adaptive applications. Such environments are also characterized by dynamically discoverable services that can be utilized by applications to improve their functionality and quality of service (QoS). Thus, application adaptation decisions not only depend on context properties, but also on service availability and QoS-properties. In this chapter we present a novel comprehensive modeling approach that facilitates the model-driven development of such applications. Our focus is on modeling concepts which align the description of services and their QoS-properties with the context modeling approach. We provide a harmonized view on context and service properties, bridging the syntactical and semantic differences through an ontology. We also consider related aspects like semantic service discovery and service level agreements.

Architectural Constraints in the Model-Driven Development of Self-Adaptive Applications

In component-based software development, a composition of connected components represents a software systems architecture. This component framework supports adaptation through application variability. The adaptation decision is made at runtime by resolving the variation points and computing the utility of all application variants. Following the application variability model, a huge number of application variants may arise, many of which are not feasible in reality. Architectural constraints may be applied to filter out such infeasible variants before checking their utilities. This article presents an approach to specify architectural constraints while following a model-driven development approach.

Modeling of component-based adaptive distributed applications

A challenge in distributed system design is to cope with the dynamic nature of the execution environment. In this paper, we present an approach for modeling adaptation of component based distributed applications. The approach supports component-based design of different variants of the applications, and a framework for selecting proper variants based on the current state of the execution environment and the user preferences. XML is used as the specification language. Transformation of the XML based design specifications to programming languages like Java is also discussed.

Heuristic Approaches for QoS-Based Service Selection

In a Service Oriented Architecture (SOA) business processes are commonly implemented as orchestrations of web services, using the Web Services Business Process Execution Language (WS-BPEL). Business processes not only have to provide the required functionality, they also need to comply with certain Quality-of-Service (QoS) constraints which are part of a service-level agreement between the service provider and the client. Different service providers may offer services with the same functionality but different QoS properties, and clients can select from a large number of service offerings. However, choosing an optimal collection of services for the composition is known to be an NP-hard problem.

Context inference of users' social relationships and distributed policy management

Inference of high-level context is becoming crucial in development of context-aware applications. An example is social context inference - i.e., deriving social relations based upon the users daily communication with other people. The efficiency of this mechanism mainly depends on the method(s) used to draw inferences based on existing evidence and sample information, such as a training data. Our approach uses rule-based data mining, Bayesian network inference, and user feedback to compute the probabilities of another user being in the specific social relationship with a user whose daily communication is logged by a mobile phone. In addition, a privacy mechanism is required to ensure the users personal integrity and privacy when sharing this users sensitive context data. Therefore, the derived social relations are used to define a users policies for context access control, which grant the restricted context information scope depending on the users current context. Finally, we propose a distributed architecture capable of managing this context information based upon these context access policies.

A component-based planning framework for adaptive systems

Recently, many researchers have focused on designing generic and reusable middlewares to overcome the complexity in building adaptive systems There is a general agreement that the openness provided by component-based approaches coupled with reflection mechanisms is the minimum prerequisites for supporting dynamic reconfigurations However, this is not sufficient to implement the heart of the adaptation loop namely the decision making on the required reconfiguration that adapts the system in a given context In this regard, this paper proposes a planning framework that subsumes and automates the adaptation decision-making in reflective component-based adaptive systems The salient feature of this framework is to model the variability of the adaptive system as a set of variation points at which alternative component compositions and implementations can be selected to form an application configuration The selection of a feasible configuration in a given context is based on the concept of component wise utility functions that estimates the user benefit of including a specific implementation alternative at a variation point in the composition We show that the selection problem can be modelled as a multi constraint shortest path that can be found in polynomial time Our approach is validated through a real world example implementing adaptive scenarios in the domain of mobile computing.

Context as a service - Requirements, design and middleware support

Context-aware self-adaptive applications monitor and exploit knowledge about external operating conditions and adapt to changes in the execution context. Modern smartphones are equipped with several sensors, like GPS sensor or accelerometer. Additionally, context reasoners and external context providers exist. Thus, it is possible that several context providers offer information of the same type (e.g. location) but differ in quality levels (e.g. accuracy), representations (e.g. position represented in coordinates and as an address) and cost (e.g. battery consumption) for providing the information. In this paper, we provide a comprehensive approach and an according middleware architecture to support the selection and activation of dynamically appearing context providers according to specific context requests. Local context providers are activated dynamically on demand in order to save resources. Furthermore we provide support to overcome heterogeneous representations of dynamically discovered context information and their metadata.

Modeling of Component-Based Self-Adapting Context-Aware Applications for Mobile Devices

A challenge in distributed system design is to cope with the dynamic nature of the execution environment. In this paper, we present a model-driven development approach for adaptive component-based applications running on mobile devices. Context dependencies and adaptation capabilities of applications are modeled in UML. We present our new modeling approach and UML profile. A short description of the required middleware infrastructure is given and the transformation technique of the UML models to platform specific code is briefly introduced. An application example illustrates the modeling and development approach. The presented research results have been obtained as part of the European IST project MADAM.