attention as an important sub#eld of software engineering. During that time there has been considerable progress in developing the technological and methodological base for treating architectural design as an engineering discipline. However, much remains to be done to achieve that goal. Moreover, the changing face of technology raises anumber of new challenges for software architecture. This paper examines some of the important trends of software architecture in research and practice, and speculates on the important emerging trends, challenges, and aspirations.

JBoss is an extensible, reflective, and dynamically reconfigurable Java application server. It includes a set of components that implement the J2EE specification, but its scope goes well beyond J2EE. JBoss is open-ended middleware, in the sense that users can extend middleware services by dynamically deploying new components into a running server. We believe that no other application server currently offers such a degree of extensibility. This paper focuses on two major architectural parts of JBoss: its middleware component model, based on the JMX model, and its meta-level architecture for generalized EJBs. The former requires a novel class loading model, which JBoss implements. The latter includes a powerful and flexible remote method invocation model, based on dynamic proxies, and relies on systematic usage of interceptors as aspect-oriented programming artifacts.

Component-based software engineering is a powerful paradigm for building large applications. However, our experience with building application of components is that the existing advanced component models (such as those offering component nesting, behavior specification and checking, dynamic reconfiguration to some extent, etc.) are subject to a lot of limitations and issues which prevent them from being accepted more widely (by industry in particular). We claim that these issues are specifically related to (a) the lack of support for dynamic reconfigurations of hierarchical architectures, (b) poor support for modeling and extendibility of the control part of a component, and (c) the lack of support for different communication styles applied in inter-component communication. In this paper, we show how these problems can be addressed and present an advanced component system SOFA 2.0 as a proof of the concept. This system is based on its predecessor SOFA, but it incorporates a number of enhancements and improvements. 1.

In speech synthesis, concatenative data-driven synthesis methods prevail. They use a database of recorded speech and a unit selection algorithm that selects the segments that match best the utterance to be synthesized. Transferring these ideas to musical sound synthesis allows a new method of high quality sound synthesis. Usual synthesis methods are based on a model of the sound signal. It is very difficult to build a model that would preserve the entire fine details of sound. Concatenative synthesis achieves this by using actual recordings. This data-driven approach (as opposed to a rule-based approach) takes advantage of the information contained in the many sound recordings. For example, very naturally sounding transitions can be synthesized, since unit selection is aware of the context of the database units. The CATERPILLAR software system has been developed to allow data-driven concatenative unit selection sound synthesis. It allows high-quality instrument synthesis with high level control, explorative free synthesis from arbitrary sound databases, or resynthesis of a recording with sounds from the database. It is based on the new software-engineering concept of component-oriented software, increasing flexibility and facilitating reuse.

Testing is an important part of any software development project, and can typically surpass more than half of the development cost. For safety-critical computer based systems, testing is even more important due to stringent reliability and safety requirements. However, most safety-critical computer based systems are real-time systems, and the majority of current testing and debugging techniques have been developed for sequential (non real-time) programs. These techniques are not directly applicable to real-time systems, since they disregard issues of timing and concurrency. This means that existing techniques for reproducible testing and debugging cannot be used. Reproducibility is essential for regression testing and cyclic debugging, where the same test cases are run repeatedly with the intention of verifying modified program code or to track down errors. The current trend of consumer and industrial applications goes from single microcontrollers to sets of distributed micro-controllers, which are even more challenging than handling real-time per-see, since multiple loci of observation and control additionally must be considered. In this thesis we try to remedy these problems by presenting an integrated approach to monitoring, testing, and debugging of distributed real-time systems. For monitoring

Event notification services enable loose coupling and they are therefore becoming an essential part of distributed systems' design. However, the development of event services follows the early stages of programming language evolution, disregarding the need for efficient mechanisms to structure event-based applications. In this paper, the well-known notion of scopes is introduced to event-based systems. We show that limiting the visibility of events is a simple yet powerful mechanism that allows to identify application structure and offers a module construct for the loosely coupled components in event-based systems. We are able to customize the semantics of scoped event notification services by binding meta-objects to the application structure that reify important aspects of notification delivery, like interface mappings and transmission policies. The scoping concept facilitates design and implementation by offering encapsulation and adaption of syntax and semantics of eventbased systems.

. In this paper we deal with object-oriented component integration issues. We argue that traditional framework customization techniques are inappropriate for componentbased programming since they lack support for non-invasive, encapsulated, dynamic customization. We propose a new language construct, called a pluggable composite adapter, for expressing component gluing. A pluggable composite adapter allows the separation of customization code from component implementation, resulting in better modularity, flexible extensibility, and improved maintenance and understandability. We also discuss alternative realizations of the construct. 1. Introduction Component software, i.e., software that is an assembly of individual, independently developed parts, is becoming the predominant architecture. We consider two factors as the driving force behind this development. First, as indicated in [22] component software represents a middle path between the two extremes that predominate traditional sof...

Abstract. Mobile client applications must discover and interoperate with application services available to them at their present location. However, these services will be developed upon a range of middleware types (e.g. RMI and publish-subscribe) and advertised using different service discovery protocols (e.g. UPnP and SLP) unknown to the application developer. Therefore, a middleware platform supporting mobile client applications should ideally adapt its behaviour to interoperate with any type of discovered service. Furthermore, these applications should be developed independently from particular middleware implementations, as the interaction type is unknown until run-time. This paper presents ReM-MoC, a reflective middleware platform that dynamically adapts both its binding and discovery protocol to allow interoperation with heterogeneous services. Furthermore, we present the ReMMoC programming model, which is based upon the Web Services concept of abstract services. We evaluate this work in terms of supporting mobile application development and the memory footprint cost of utilising reflection to create a mobile middleware platform. 1

Building distributed embedded systems from scratch is not cost-effective. Instead, designing and building these systems by using domain specific components has promise. However, in using components, the most difficult issues are ensuring that hidden dependencies won't cause failures and that non-functional properties such as real-time performance are being met. We have built the VEST toolkit whose aim is to provide a rich set of dependency checks based on the concept of aspects to support distributed embedded system development via components. We describe the toolkit and its novelty. We also use VEST on two case studies of a CORBA-based middleware for avionics. Data collected shows that VEST can significantly reduce the time it takes to build a distributed real-time embedded system by over 50%.

Significant economic and technical benefits accrue from the use of pre-existing and commercially available software components to develop new systems. However, challenges remain that, if not adequately addressed, will slow the adoption of software component technology. Chief among these are a lack of consumer trust in the quality of components, and a lack of trust in the quality of assemblies of components without extensive and expensive testing. This paper