Software architectures shift the focus of developers from lines-of-code to coarser-grained architectural elements and their overall interconnection structure. Architecture description languages (ADLs) have been proposed as modeling notations to support architecture-based development. There is, however, little consensus in the research community on what is an ADL, what aspects of an architecture should be modeled in an ADL, and which of several possible ADLs is best suited for a particular problem. Furthermore, the distinction is rarely made between ADLs on one hand and formal specification, module interconnection, simulation, and programming languages on the other. This paper attempts to provide an answer to these questions. It motivates and presents a definition and a classification framework for ADLs. The utility of the definition is demonstrated by using it to differentiate ADLs from other modeling notations. The framework is used to classify and compare several existing ADLs, enabling us in the process to identify key properties of ADLs. The comparison highlights areas where existing ADLs provide extensive support and those in which they are deficient, suggesting a research agenda for the future.

The World Wide Web has succeeded in large part because its software architecture has been designed to meet the needs of an Internet-scale distributed hypermedia system. The Web has been iteratively developed over the past ten years through a series of modifications to the standards that define its architecture. In order to identify those aspects of the Web that needed improvement and avoid undesirable modifications, a model for the modern Web architecture was needed to guide its design, definition, and deployment. Software architecture research investigates methods for determining how best to partition a system, how components identify and communicate with each other, how information is communicated, how elements of a system can evolve independently, and how all of the above can be described using formal and informal notations. My work is motivated by the desire to understand and evaluate the architectural design of network-based application software through principled use of architectural constraints, thereby obtaining the functional, performance, and social properties desired of an architecture. An architectural style is a named, coordinated set of architectural constraints. This dissertation defines a framework for understanding software architecture via architectural styles and demonstrates how styles can be used to guide the architectural design of network-based application software. A survey of architectural styles for network-based applications is used to classify styles according to the architectural properties they induce on an architecture for distributed hypermedia. I then introduce the Representational State Transfer (REST) architectural style and describe how REST has been used to guide the design and development of the architecture for the modern Web. REST emphasizes scalability of component interactions, generality of interfaces, independent deployment of components, and intermediary components to reduce interaction latency, enforce security, and encapsulate legacy systems. I describe the software engineering principles guiding REST and the interaction constraints chosen to retain those principles, contrasting them to the constraints of other architectural styles. Finally, I describe the lessons learned from applying REST to the design of the Hypertext Transfer Protocol and Uniform Resource Identifier standards, and from their subsequent deployment in Web client and server software.

Abstract. Web Services will transform the web from a collection of information into a distributed device of computation. In order to employ their full potential, appropriate description means for web services need to be developed. For this purpose we define a fullfledged Web Service Modeling Framework (WSMF) that provides the appropriate conceptual model for developing and describing web services and their composition (complex web services). Spoken in a nutshell its philosophy is based on the following principle: maximal de-coupling complemented by scalable mediation service.

Continuous availability is a critical requirement for an important class of software systems. For these systems, runtime system evolution can mitigate the costs and risks associated with shutting down and restarting the system for an update. We present an architecture-based approach to runtime software evolution and highlight the role of software connectors in supporting runtime change. An initial implementation of a tool suite for supporting the runtime modification of software architectures, called ArchStudio, is presented. 1

: Separation of concerns is at the core of software engineering, and has been for decades. This has led to the invention of many interesting, and effective, modularization approaches. Yet many of the problems it is supposed to alleviate are still with us, including dangerous and expensive invasive change, and obstacles to reuse and component integration. A key reason is that one needs different decompositions according to different concerns at different times, but most languages and modularization approaches support only one "dominant" kind of modularization (e.g., by class in object-oriented languages). Once a system has been decomposed, extensive refactoring and reengineering are needed to remodularize it. Multi-dimensional separation of concerns allows simultaneous separation according to multiple, arbitrary kinds (dimensions) of concerns, with on-demand remodularization. Concerns can overlap and interact. This paper discusses multi-dimensional separation of concerns in general, our particular approach to providing it, called hyperspaces , and our support for hyperspaces in Java^TM , called Hyper/J^TM. 2 Chapter # 1.

Ubiquitous computing poses a number of challenges for software architecture.

Software architecture describes the structure of a system, enabling more effective design, program understanding, and formal analysis. However, existing approaches decouple implementation code from architecture, allowing inconsistencies, causing confusion, violating architectural properties, and inhibiting software evolution. ArchJava is an extension to Java that seamlessly unifies software architecture with implementation, ensuring that the implementation conforms to architectural constraints. A case study applying ArchJava to a circuit-design application suggests that ArchJava can express architectural structure effectively within an implementation, and that it can aid in program understanding and software evolution.

In this paper, we propose a means to enhance an architecture description language with a description of component behavior. A notation used for this purpose should be able to express the "interplay" on the component's interfaces and reflect step-by-step refinement of the component's specification during its design. In addition, the notation should be easy to comprehend and allow for formal reasoning about the correctness of the specification refinement and also about the correctness of an implementation in terms of whether it adheres to the specification. Targeting all these requirements together, the paper proposes to employ behaviorprotocols which are based on a notation similar to regular expressions.

Software architectures have the potential to substantially improve the development and evolution of large, complex, multi-lingual, multi-platform, long-running systems. However, in order to achieve this potential, specific techniques for architecture-based modeling, analysis, and evolution must be provided. Furthermore, one cannot fully benefit from such techniques unless support for mapping an architecture to an implementation also exists. This paper motivates and presents one such approach, which is an outgrowth of our experience with systems developed and evolved according to the C2 architectural style. We describe an architecture description language (ADL) specifically designed to support architecturebased evolution and discuss the kinds of evolution the language supports. We then describe a component-based environment that enables modeling, analysis, and evolution of architectures expressed in the ADL, as well as mapping of architectural models to an implementation infrastructure. The architecture of the environment itself can be evolved easily to support multiple ADLs, kinds of analyses, architectural styles, and implementation platforms. Our approach is fully reflexive: the environment can be used to describe, analyze, evolve, and (partially) implement itself, using the very ADL it supports. An existing architecture is used throughout the paper to provide illustrations and examples. Keywords Software architecture, architecture description language,

The use of component models such as Enterprise Java Beans and the CORBA Component Model (CCM) in application development is expanding rapidly. Even in real-time safety/mission-critical domains, component-based development is beginning to take hold as a mechanism for incorporating non-functional aspects such as realtime, quality-of-service, and distribution. To form an effective basis for development of such systems, we believe that support for reasoning about correctness properties of component-based designs is essential. In this paper, we present Cadena – an integrated environment for building and modeling CCM systems. Cadena provides facilities for defining component types using CCM IDL, specifying dependency information and transition system semantics for these types, assembling systems from CCM components, visualizing various dependence relationships between components, specifying and verifying correctness properties of models of CCM systems derived from CCM IDL, component assembly information, and Cadena specifications, and producing CORBA stubs and skeletons implemented in Java. We are applying Cadena to avionics applications built using Boeing’s Bold Stroke framework. 1.