Eric M. Dashofy

An infrastructure for the rapid development of XML-based architecture description languages

Research and experimentation in software architectures over the past decade have yielded a plethora of software architecture description languages (ADLs). Continuing innovation indicates that it is reasonable to expect more new ADLs, or at least ADL features. This research process is impeded by the difficulty and cost associated with developing new notations. An architect in need of a unique set of modeling features must either develop a new architecture description language from scratch or undertake the daunting task of modifying an existing language. In either case, it is unavoidable that a significant effort will be expended in building or adapting tools to support the language. To remedy this situation, we have developed an infrastructure for the rapid development of new architecture description languages. Key aspects of the infrastructure are its XML-based modular extension mechanism, its base set of reusable and customizable architectural modeling constructs, and its equally important set of flexible support tools. This paper introduces the infrastructure and demonstrates its value in the context of several real-world applications.

A highly-extensible, XML-based architecture description language

Software architecture research focuses on models of software architectures as specified in architecture description languages (ADLs). As research progresses in specific areas of software architectures, more and more architectural information is created. Ideally, this information can be stored in the model. An extensible modeling language is crucial to experimenting with and building tools for novel modeling constructs that arise from evolving research. Traditional ADLs typically support a small set of modeling constructs very well, but adapt to others poorly. XML provides an ideal platform upon which to develop an extensible modeling language for software architectures. Previous XML-based ADLs successfully leveraged XMLs large base of off-the-shelf tool support, but did not take advantage of its extensibility. To give software architecture researchers more freedom to explore new possibilities and modeling techniques, while maximizing reuse of tools and modeling constructs, we have developed xADL 2.0, a highly extensible XML-based ADL. xADL 2.0 supports run-time and design time modeling, architecture configuration management and model-based system instantiation. Additionally, xADL 2.0 has a set of extensible infrastructure tools that support the creation, manipulation, and sharing of xADL 2.0 documents.

Towards architecture-based self-healing systems

Our approach to creating self-healing systems is based on software architecture, where repairs are done at the level of a software systems components and connectors. In our approach, event-based software architectures are targeted because they offer significant benefits for run-time adaptation. Before an automated planning agent can decide how to repair a self-healing system, a significant infrastructure must be in place to support making the planned repair. Specifically, the self-healing system must be built using a framework that allows for run-time adaptation, there must be a language in which to express the repair plan, and there must be a reconfiguration agent that can execute the repair plan once it is created. In this paper, we present tools and methods that implement these infrastructure elements in the context of an overall architecture-based vision for building self-healing systems. The paper concludes with a gap analysis of our current infrastructure vs. the overall vision, and our plans for fulfilling that vision.

A comprehensive approach for the development of modular software architecture description languages

Research over the past decade has revealed that modeling software architecture at the level of components and connectors is useful in a growing variety of contexts. This has led to the development of a plethora of notations for representing software architectures, each focusing on different aspects of the systems being modeled. In general, these notations have been developed without regard to reuse or extension. This makes the effort in adapting an existing notation to a new purpose commensurate with developing a new notation from scratch. To address this problem, we have developed an approach that allows for the rapid construction of new architecture description languages (ADLs). Our approach is unique because it encapsulates ADL features in modules that are composed to form ADLs. We achieve this by leveraging the extension mechanisms provided by XML and XML schemas. We have defined a set of generic, reusable ADL modules called xADL 2.0, useful as an ADL by itself, but also extensible to support new applications and domains. To support this extensibility, we have developed a set of reflective syntax-based tools that adapt to language changes automatically, as well as several semantically-aware tools that provide support for advanced features of xADL 2.0. We demonstrate the effectiveness, scalability, and flexibility of our approach through a diverse set of experiences. First, our approach has been applied in industrial contexts, modeling software architectures for aircraft software and spacecraft systems. Second, we show how xADL 2.0 can be extended to support the modeling features found in two different representations for modeling product-line architectures. Finally, we show how our infrastructure has been used to support its own development. The technical contribution of our infrastructure is augmented by several research contributions: the first decomposition of an architecture description language into modules, insights about how to develop new language modules and a process for integrating them, and insights about the roles of different kinds of tools in a modular ADL-based infrastructure.

Moving architectural description from under the technology lamppost

Software architecture description languages (ADLs) were a particularly active research area in the 1990s. In 2000, the author co-authored an extensive study of existing ADLs, which has served as a useful reference to software architecture researchers and practitioners. However, the field of software architecture and our understanding of it have undergone a number of changes in the past several years. In particular, the Unified Modeling Language (UML) has gained a lot of popularity and wide adoption, and as a result many of the ADLs the author had studied have been pushed into obscurity. In this paper, the author argues that the main reason behind this is that the early ADLs focused almost exclusively on the technological aspects of architecture, and mostly ignored the application domain and business contexts within which software systems, and development organizations, exist. Together, these three concerns - technology, domain, and business -constitute the three lampposts needed to appropriately illuminate software architecture and architectural description. The author use this new framework to evaluate both the languages from my original study, as well as several more recent ADLs (including UML 2.0)

Using off-the-shelf middleware to implement connectors in distributed software architectures

Software architectures promote development focused on modular building blocks and their interconnections. Since architecture-level components often contain complex functionality, it is reasonable to expect that their interactions will also be complex. Modeling and implementing software connectors thus becomes a key aspect of architecture-based development. Software interconnection and middleware technologies such as RMI, CORBA, ILU, and ActiveX provide a valuable service in building applications from components. The relation of such services to software connectors in the context of software architectures, however, is not well understood. To understand the tradeoffs among these technologies with respect to architectures, we have evaluated several off-the-shelf middleware technologies and identified key techniques for utilizing them in implementing software connectors. Our platform for investigation was C2, a component- and message-based architectural style. By encapsulating middleware functionality within software connectors, we have coupled C2s existing benefits such as component interchangeability, substrate independence and structural guidance with new capabilities of multi-lingual, multi-process and distributed application development in a manner that is transparent to architects.

The Role of Middleware in Architecture-Based Software Development

Software architectures promote development focused on modular functional building blocks (components), their interconnections (configurations), and their interactions (connectors). Since architecture-level components often contain complex functionality, it is reasonable to expect that their interactions will be complex as well. Middleware technologies such as CORBA, COM, and RMI provide a set of predefined services for enabling component composition and interaction. However, the potential role of such services in the implementations of software architectures is not well understood. In practice, middleware can resolve various types of component heterogeneity — across platform and language boundaries, for instance — but also can induce unwanted architectural constraints on application development. We present an approach in which components communicate through architecture-level software connectors that are implemented using middleware. This approach preserves the properties of the architecture-level connectors while leveraging the beneficial capabilities of the underlying middleware. We have implemented this approach in the context of a component- and message-based architectural style called C2 and demonstrated its utility in the context of several diverse applications. We argue that our approach provides a systematic and reasonable way to bridge the gap between architecture-level connectors and implementation-level middleware packages.

ArchStudio 4: An Architecture-Based Meta-Modeling Environment

We will demonstrate ArchStudio, an environment for software architecture modeling and meta-modeling. We will also showcase a set of innovative architecture-centric applications that use ArchStudio technologies as their basis.

Representing Product Family Architectures in an Extensible Architecture Description Language

Product family architectures need to be captured much like regular software architectures. Unfortunately, representations for product family architectures are scarce and a deep understanding of all of the necessary features of such representations is still lacking. In this paper, we introduce an extensible XML-based representation that is suitable as a basis for rapidly defining new representations for product family architectures. We describe some of the details of this representation and present how Koala and Mae, two early representations for product family architectures, can be mapped onto our XML-based representation with relatively little effort.

An (architecture-centric) approach for tracing, organizing, and understanding events in event-based software architectures

Applications built in a strongly decoupled, event-based interaction style have many commendable characteristics, including ease of dynamic configuration, accommodation of platform heterogeneity, and ease of distribution over a network. It is not always easy, however, to humanly grasp the dynamic behavior of such applications, since many threads are active and events are asynchronously (and profusely) transmitted. This paper presents a novel, complete approach that aids in the understanding, debugging, and visualization of the behaviors of event-based applications. It applies to real, implemented systems, without requiring the presence of component source code, and supports partial or incomplete, heuristic behavior specifications. A prototype implementation of our approach was applied to two systems, including the prototype itself, indicating that our approach is feasible, scalable, and shows promising results in terms of increasing the understandability of these types of systems.