This paper argues for a set of requirements that an architectural style for self-healing systems should satisfy: adaptability, dynamicity, awareness, autonomy, robustness, distributability, mobility, and traceability. Support for these requirements is discussed along five dimensions we have identified as distinguishing characteristics of architectural styles: external structure, topology rules, behavior, interaction, and data flow. As an illustration, these requirements are used to assess an existing architectural style. While this initial formulation of the requirements appears to have utility, much further work remains to be done in order to apply it in evaluating and comparing architectural styles for self-healing systems. 1

CWI is a founding member of ERCIM, the European Research Consortium for Informatics and Mathematics. CWI's research has a theme-oriented structure and is grouped into four clusters. Listed below are the names of the clusters and in parentheses their acronyms.

Abstract When designing a mobile application, we have to be aware of the properties and facilities of the target platform. At a conceptual level, this platform can be specified by a style, defining the structures and operations available to applications. In this paper, we use a UML-like meta model for the structural aspect and graph transformation rules over its instances to specify the dynamics of a style of mobile systems. The model is layered to separate clearly the software from the hardware and the geographic view of the system.

Abstract. We present SynchNet, a compositional meta-level language for coordination of distributed. Its design is based on the principle of separation of concerns, namely separation of the coordination from computational aspects. SynchNet can be used in combination with any objectbased language capable of expressing sequential behavior of objects. SynchNet, which is inspired by Petri nets, has a simple syntax and semantics, but is expressive enough to code many of the commonly used coordination patterns. The level of abstraction that it provides allows tools and techniques developed for Petri nets to be readily applied to analysis and verification of the specified coordination patterns.

Service-oriented development offers a novel architectural approach that addresses crucial char-acteristics of modern business process development such as dynamic evolution, intra- and inter-enterprise cooperation, and distribution/mobility. In previous papers, we have shown how the mechanisms that regulate the relationships, functioning and cooperation of business activities in such architectural models can be externalised from business rules in terms of connectors that can be superposed dynamically on stable core business entities. That is to say, we focused on what, in the literature, has been called the ”service composition layer ” of service-oriented architectures or, for short, their ”composition logic”. Our emphasis in this paper is on the distribution aspects: we show how a corresponding ”dis-tribution logic ” can be defined in terms of another set of architectural primitives that address the way business rules depend on ”locations”. These primitives address what are sometimes called ”business channels ” (ATMs, PDAs, Pay-TV, Internet, inter alia) as offered in typical contem-porary ICT-infrastructures with substantial added-value to business processes. We argue that interacting (core) business entities located at or endowed with such mobility/distribution capabil-ities should be modelled in a way that separates the composition from the distribution logic so that business interactions can be understood and evolved in a location-transparent way. Our approach is based on a mathematical model that we have recently developed for modelling context-aware interactions. An example from banking is used for illustrating its applicability.

Abstract. Architectural styles represent composition patterns and constraints at the software architectural level and are targeted at families of systems with shared characteristics. They enable architectural reuse and hence can bring economy to the design of software architecture. Existing approaches support systematic description of style-based software architectures. Our approach, Alfa, focuses on the construction, instead of description, of style-based software architectures using architectural primitives. This is based on our observation that architectural styles and, indeed, software architectures share many underlying concepts that lead to architectural primitives. Previously, Alfa’s primitives were shown to be sufficient for modeling architectural styles. In this paper, we present the composition of a diverse set of styles for network-based systems using xAlfa, a systematic notation for composing styles from Alfa’s primitives. We then show that two reuse mechanisms in xAlfa, inheritance and composition, enable concise style compositions and unambiguously bring out similarities among architectural styles. 1

Abstract. The growing importance of context-awareness in the construction of adaptable systems requires the development of formal models and notations that can bring this new dimension from middleware concerns into the higher levels of modelling. In this paper, we propose a formal approach to the design of con-text-aware systems that is well integrated with the concepts and techniques that have been proposed for software architectures. This approach is based on a set of primitives through which the notion of context can be modelled as a first-class entity and context-awareness addressed explicitly as an additional dimen-sion of architectural elements. We illustrate the approach around an image search system. 1

COMMUNITY is a formal approach to software architecture. It has a precise, yet intuitive mathematical semantics based on category theory. It supports, at the methodological level, a clear separation between computation, coordination, and distribution (including mobility). It provides a simple state-based language for describing component behaviour that is inspired by Unity and Interacting Processes. It also addresses composition as a first class concern and accounts for the emergence of global system properties from interconnections. This paper describes the approach and available tool support by modelling essential aspects of the GSM handover protocol. We also sketch a framework that we are implementing for the distributed execution of such specifications using Klava, a Java library for mobile agent systems based on tuple spaces.

A common approach to defining architectural views is to have independent heterogeneous representations that are tailored to each view’s purpose, but this makes reconciling views into an overall architectural description harder. In this paper we put forward a complementary (not alternative) approach in which some views are derived from a given architecture description language (ADL) in a systematic way, by listing the design questions each view should answer. The approach is based on constructing the language’s metamodel and extending it with the entities and associations needed to capture and explicitly relate the required views. 1.