Program behavior that relies on contextual information, such as physical location or network accessibility, is common in today's applications, yet its representation is not sufficiently supported by programming languages. With context-oriented programming (COP), such context-dependent behavioral variations can be explicitly modularized and dynamically activated. In general, COP could be used to manage any context-specific behavior. However, its contemporary realizations limit the control of dynamic adaptation. This, in turn, limits the interaction of COP's adaptation mechanisms with widely used architectures, such as event-based, mobile, and distributed programming. The JCop programming language extends Java with language constructs for context-oriented programming and additionally provides a domain-specific aspect language for declarative control over runtime adaptations. As a result, these redesigned implementations are more concise and better modularized than their counterparts using plain COP. JCop's main features have been described in our previous publications. However, a complete language specification has not been presented so far. This report presents the entire JCop language including the syntax and semantics of its new language constructs. / Das Verhalten von modernen Software-Anwendungen benötigt häufig Informationen über den Kontext ihrer Ausführung, z.B. die geografische Position, die Tageszeit oder die aktuelle Netzwerkbandbreite. Dennoch bieten heutige Programmiersprachen nur wenig Unterstützung für die Repräsentation kontextspezifischen Verhaltens. Kontextorientiertes Programmieren ist ein Ansatz, der die explizite Modularisierung und Laufzeitaktivierung von kontextspezifischem Verhalten auf der Ebene von Programmiersprachkonstrukten ermöglicht. Die bisherigen Umsetzungen von kontextorientiertem Programmieren schränken jedoch die Kontrolle der Laufzeitaktivierungen solches kontextspezifischen Verhaltens ein. Daraus folgt eine Einschränkung der Anwendungsbereiche für kontextorientiertes Programmieren, unter anderem für solche Domänen, in denen Programme sehr häufig kontextabhängiges Verhalten bereitstellen, z.B. ereignisbasierte, mobile und dienstorientierte Systeme. Die Programmiersprache JCop erweitert Java um Sprachkonstrukte für kontextorientieres Programmieren und bietet zusätzlich eine domänenspezifische Aspektsprach an, mit deren Hilfe Laufzeitadaptionen deklarativ spezifiziert werden können. Die Kernkonzepte von JCop wurden bereits in mehrern Publikationen vorgestellt, dieser Bericht enthält nun eine umfassende Sprachspezifikation von JCop.

Context-aware computing requires software that can adapt to changes in context. When contextual circumstances trigger multiple adaptations, software must also understand the relationships between these adaptations and react according to the rules governing these relationships. Adaptable software needs a means to establish and interpret these rules in order to avoid any undesirable and potentially catastrophic conflicts. This dissertation designs and implements the Adaptation Rules Management API (ArmAPI). ArmAPI has been demonstrated to work with a Context-Oriented Programming variation for Java called ContextJ* to execute conflict-free adaptations in two software applications. ArmAPI allows programmers to define relationship types between adaptations, and transfers these definitions to Prolog facts and rules. The Prolog engine, encapsulated within ArmAPI, then works with imperative algorithms to determine the appropriate adaptations to execute based on the current set of facts, rules, and contextual circumstances. Context represents all of the conditions for all of the entities known to an observing device. In any environment, context represents a large amount of data that can influence a multitude of conflicting adaptations. This research provides an incremental step towards overcoming the problem of adaptation conflict by constructing an API that considers the relationship types of inclusion, exclusion, ordering, conditional dependency, and independence. The API has been validated via two prototypes that provide typical scenarios.

In the vision of Ambient Intelligence, people are assisted in their everyday activities through the proactive, opportunistic support of non-intrusive computing devices offering intuitive interaction modalities. The usefulness and quality of delivered services can be improved considerably if the devices are able to adapt their behaviour according to sensed changes in their surrounding environment, both at the physical and logical levels. This interplay between context-awareness and dynamic software adaptability is key to the construction of applications that are smart with respect to user needs. Unfortunately, most current applications do not reach this level of adaptability, due to a lack of appropriate programming technology. Most applications exhibit fixed functionality and seldom do they sense their environment and adapt their services in a context-aware fashion. Many chances of delivering improved services to users and network peers are thus missed. This dissertation presents a programming model to ease the construction of applications that can react to changes in their execution context by adapting their behaviour dynamically. The starting point of our research is the development of novel language abstractions and the adaptation of existing abstractions to render context-aware, self-adaptable applications easier to develop. We demonstrate that a simple yet powerful computation model readily provides the needed support, leading to straightforward application code that is not concerned with context adaptation, behaviour that can be adapted dynamically to different contexts in a non-intrusive fashion, and context-aware applications with software architectures that are not biased towards context adaptation ---rather, they can be designed freely according to their domain. The proposed computation model is realised through the Ambience programming language, and its underlying open implementation, the Ambient Object System. A small-step operational semantics describes it formally. Much in the vein of prototype-based programming, the model has been designed with simplicity and concreteness in mind. It is highly dynamic, featuring dynamic (multiple) dispatch, dynamic inheritance, dynamic typing, and dynamic method scoping. Application logic adaptation is enabled by means of an intuitive, first-class reification of context that is straightforwardly connected to dynamic behaviour selection. We describe needed management techniques for such context, and a few programming guidelines on how to develop context-aware applications using our approach. The approach is validated by showing its application in a number of scenarios inspired on Ambient Intelligence.