Nenad Medvidovic

A classification and comparison framework for software architecture description languages

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.

An architecture-based approach to self-adaptive software

Self-adaptive software requires high dependability robustness, adaptability, and availability. The article describes an infrastructure supporting two simultaneous processes in self-adaptive software: system evolution, the consistent application of change over time, and system adaptation, the cycle of detecting changing circumstances and planning and deploying responsive modifications.

Architecture-based runtime software evolution

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.

Towards a taxonomy of software connectors

Software systems of today are frequently composed of prefabricated, heterogeneous components that provide complex functionality and engage in complex interactions. Existing research on component based development has mostly focused on component structure, interfaces, and functionality. Recently, software architecture has emerged as an area that also places significant importance on component interactions, embodied in the notion of software connectors. However, the current level of understanding and support for connectors has been insufficient. This has resulted in their inconsistent treatment and a notable lack of understanding of what the fundamental building blocks of software interaction are and how they can be composed into more complex interactions. The paper attempts to address this problem. It presents a comprehensive classification framework and taxonomy of software connectors. The taxonomy is obtained through an extensive analysis of existing component interactions. The taxonomy is used both to understand existing software connectors and to suggest new, unprecedented connectors. We demonstrate the use of the taxonomy on the architecture of a large, existing system.

A language and environment for architecture-based software development and evolution

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 architecture-based 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.

Runtime software adaptation: framework, approaches, and styles

Our ICSE 1998 paper showed how an application can be adapted at runtime by manipulating its architectural model. In particular, our paper demonstrated the beneficial role of (1) software connectors in aiding runtime change, (2) an explicit architectural model fielded with the system and used as the basis for runtime change, and (3) architectural style in providing both structural and behavioral constraints over runtime change. This paper examines runtime evolution in the decade hence. A broad framework for studying and describing evolution is introduced that serves to unify the wide range of work now found in the field of dynamic software adaptation. This paper also looks to the future, identifying what we believe to be highly promising directions.

Early prediction of software component reliability

The ability to predict the reliability of a software system early in its development, e.g., during architectural design, can help to improve the systems quality in a cost-effective manner. Existing architecture-level reliability prediction approaches focus on system-level reliability and assume that the reliabilities of individual components are known. In general, this assumption is unreasonable, making component reliability prediction an important missing ingredient in the current literature. Early prediction of component reliability is a challenging problem because of many uncertainties associated with components under development. In this paper we address these challenges in developing a software component reliability prediction framework. We do this by exploiting architectural models and associated analysis techniques, stochastic modeling approaches, and information sources available early in the development lifecycle. We extensively evaluate our framework to illustrate its utility as an early reliability prediction approach.

A style-aware architectural middleware for resource-constrained, distributed systems

A recent emergence of small, resource-constrained, and highly mobile computing platforms presents numerous new challenges for software developers. We refer to development in this new setting as programming-in-the-small-and-many (Prism). This paper provides a description and evaluation of Prism-MW, a middleware platform intended to support software architecture-based development in the Prism setting. Prism-MW provides efficient and scalable implementation-level support for the key aspects of Prism application architectures, including their architectural styles. Additionally, Prism-MW is extensible to support different application requirements suitable for the Prism setting. Prism-MW has been applied in a number of applications and used as an educational tool in graduate-level software architecture and embedded systems courses. Recently, Prism-MW has been successfully evaluated by a major industrial organization for use in one of their key distributed embedded systems. Our experience with the middleware indicates that the principles of architecture-based software development can be successfully, and flexibly, applied in the Prism setting.

Integrating architecture description languages with a standard design method

Software architecture descriptions are high-level models of software systems. Some researchers have proposed special-purpose architectural notations that have a great deal of expressive power but are not well integrated with common development methods. Others have used mainstream development methods that are accessible to developers, but lack semantics needed for extensive analysis. We describe an approach to combining the advantages of these two ways of modeling architectures. We present two examples of extending UML, an emerging standard design notation, for use with two architecture description languages, C2 and Wright. Our approach suggests a practical strategy for bringing architectural modeling into wider use, namely by incorporating substantial elements of architectural models into a standard design method.

ADLs and dynamic architecture changes

Existing ADLs typically support only static architecture specification and do not provide facilities for the support of dynamically changing architectures. This paper presents a possible solution to this problem: in order to adequately support dynamic architecture changes, ADLs can leverage techniques used in dynamic programming languages. In particular, changes to ADL specifications should be interpreted. To enable interpretation, an ADL should have an architecture construction component that supports explicit and incremental specification of architectural changes, in addition to the traditional architecture description facilities. This will allow software architects to specify the changes to an architecture after it has been built. The paper expands upon the results from an ongoing project -building a development environment for CZstyle architectures.’