Abstract not found

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.

There is a real need for clear and sound design specifications of distributed systems at the architectural level. This is the level of the design which deals with the high-level organisation of computational elements and the interactions between those elements. The paper presents the Darwin notation for specifying this high-level organisation. Darwin is in essence a declarative binding language which can be used to define hierarchic compositions of interconnected components. Distribution is dealt with orthogonally to system structuring. The language supports the specification of both static structures and dynamic structures which may evolve during execution. The central abstractions managed by Darwin are components and services. Services are the means by which components interact. In addition to its use in specifying the architecture of a distributed system, Darwin has an operational semantics for the elaboration of specifications such that they may be used at runtime to di...

Architectures for software use rich abstractions and idioms to describe system components, the nature of interactions among the components, and the patterns that guide the composition of components into systems. These abstractions are higher-level than the elements usually supported by programming languages and tools. They capture packaging and interaction issues as well as computational functionality. Well-established (if informal) patterns guide architectural design of systems. We sketch a model for defining architectures and present an implementation of the basic level of that model. Our purpose is to support the abstractions used in practice by software designers. The implementation provides a testbed for experiments with a variety of system construction mechanisms. It distinguishes among different types of components and different ways these components can interact. It supports abstract interactions such as data flow and scheduling on the same footing as simple procedure...

As software systems become more complex, the overall system structure---or software architecture---becomes a central design problem. A system's architecture provides a model of the system that suppresses implementation detail, allowing the architect to concentrate on the analyses and decisions that are most crucial to structuring the system to satisfy its requirements. Unfortunately, current representations of software architecture are informal and ad hoc. While architectural concepts are often embodied in infrastructure to support specific architectural styles and in the initial conceptualization of a system configuration, the lack of an explicit, independently-characterized architecture or architectural style significantly limits the benefits of software architectural design in current practice. In this dissertation, I show that an Architecture Description Language based on a formal, abstract model of system behavior can provide a practical means of describing and analyzing softwar...

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

There is increasing interest in having software systems execute and interoperate over the Internet. Execution and interoperation at this scale imply a degree of loose coupling and heterogeneity among the components from which such systems will be built. One common architectural style for distributed; loosely-coupled, heterogeneous software systems is a structure based on event generation, observation and notification. The technology to support this approach is well-developed for local area networks, but it is illsuited to networks on the scale of the Internet. Hence, new technologies are needed to support the construction of large-scale, event-based software systems for the Internet. We have begun to design a new facility for event observation and notification that better serves the needs of Internet-scale applications. In this paper we present results from our first step in this design process, in which we defined a framework that captures many of the relevant design dimensions. Our framework comprises seven models-an object model, an event model, a naming model, an observation model, a time model, a notification model, and a resource model. The paper discusses each of these models in detail and illustrates them using an example involving an update to a Web page. The paper also evaluates three existing technologies with respect to the seven models.

a "one-of-a-kind" process, where most software is developed from scratch, even though much of the code is similar to code written for other applications. The cost of these systems can be drastically reduced and the capability of these systems improved by providing a suitable software framework for all R&A sys~ terns, We describe a novel software framework, based on the notion of dynamically reconfigurable software for sensor-based control systems. Tools to support the implementation of this framework have been built into the Chimera 3.0 Real-Time Operating System. The framework provides for the systematic development and predictable execution of flexible R&A applications while maintaining the ability to reuse code f)om previous applications. It combines object-oriented design of software with port-automaton design of digital control systems. A control module is an instance of a class of port-based objects. A task set is formed by integrating objects from a module library to form a specific configuration. An implementation using global state variables for the automatic integration of port-based objects is presented. A control subsystem is a collection of jobs which are executed one at a time, and can be programmed by a user. Multiple control subsystems can execute in parallel, and operate either independently or cooperatively. One of the fundamental concepts of reconfigurable software design is that modules are developed independent of the target hard- ware. Our framework defines classes of reconfigurable device driver objects for proving hardware independence to IJO devices, sensors, actuators, and special purpose processors. Hardware independent real-time communication mechanisms for inter-subsystem eommurtication are also described. A/ong with providing a foundatio...

Abstract not found