R.N. Taylor’s research while affiliated with CA Technologies and other places

To guard against malicious peers, peer-to-peer applications must incorporate suitable trust mechanisms. Current decentralized trust-management research focuses mainly on producing trust models and algorithms, whereas the actual composition of trust models into real applications has been largely unexplored. The practical architectural approach for composing egocentric trust (Pace) provides detailed design guidance on where and how developers can incorporate trust models into decentralized applications. In addition, Pace's guiding principles promote countermeasures against threats to decentralized systems. Several prototypes demonstrate the approach's use and feasibility.

We present an architectural style to directly support the formal and informal relationships that underlie work activity. Rather than defining the dependencies between activities, our focus is on the structure of coordination within the organization. The approach is guided by a need for scoped information and communication spaces, decentralized ownership of work product and process, and support for varying levels of work definition, integrating structured models of work process with ad-hoc activities. The base of the approach is a peer-to-peer style with peers supporting work participants. Peers are subdivided into active task spaces, associating information resources, software components, and communication. Independent connectors define the relationships between peers and provide the mechanism for defining larger more complex structures. This paper describes the style in detail and discusses a prototype implementation.

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.

Distributed applications that lack a central, trustworthy authority for control and validation are properly termed decentralized. Multiple, independent agencies, or "partners", cooperate to achieve their separate goals. Issues of trust are paramount for designers of such partners. While the research literature has produced a variety of trust technology building blocks, few have attempted to articulate how these various technologies can regularly be composed to meet trust goals. This paper presents a particular, event-based, architectural style, PACE, that shows where and how to incorporate various types of trust-related technologies within a partner, positions the technologies with respect to the rest of the application, allows variation in the underlying network model, and works in a dynamic setting. Initial experiments with variants of two sample decentralized applications developed in the PACE style reveal the virtues of dealing with all aspects of application structure and trust in a comprehensive fashion.

Because it takes time and trust to establish agreement, traditional consensus-based architectural styles cannot safely accommodate resources that change faster than it takes to transmit notification of that change, nor resources that must be shared across independent agencies. The alternative is decentralization: permitting independent agencies to make their own decisions. Our definition contrasts with that of distribution, in which several agents share control of a single decision. Ultimately, the physical limits of network latency and the social limits of independent agency call for solutions that can accommodate multiple values for the same variable. Our approach to this challenge is architectural: proposing constraints on the configuration of components and connectors to induce particular desired properties of the whole application. Specifically, we present, implement, and evaluate variations of the World Wide Web's Representational State Transfer (REST) architectural style that support distributed and decentralized systems.

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 to humanly grasp the dynamic behavior of such applications, since many threads are active and events are asynchronously (and profusely) transmitted. We present a set of requirements for an aid to assist in the human understanding and exploration of the behavior of such applications through the incremental refinement of rules for determining causality relationships between messages sent among components. A prototype tool is presented, indicating one viable approach to meeting these requirements. Experience with the tool reinforces some of the requirements and indicates others.

In order to support architecture-centric tool integration within the ArchStudio 2.0 Integrated Development Environment (IDE), we adopted Extensible Markup Language (XML) to represent the shared architecture-in-progress. Since ArchStudio is an architectural style-based development environment that incorporates an extensive number of tools, including commercial off-the-shelf products, we developed a new, vendor-neutral, ADL-neutral interchange format called Extensible Architecture description Language (xADL), as well as a "vocabulary" specific to the C2 style (xC2). This paper outlines our vision for representing architectures as hypertext, the design rationale behind xADL and xC2, and summarizes our engineering experience with this strategy.

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 XML's 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

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