George Edwards

PLASMA: a plan-based layered architecture for software model-driven adaptation

Modern software-intensive systems are expected to adapt, often while the system is executing, to changing requirements, failures, and new operational contexts. This paper describes an approach to dynamic system adaptation that utilizes plan-based and architecture-based mechanisms. Our approach utilizes an architecture description language (ADL) and a planning-as-model-checking technology to enable dynamic replanning. The ability to automatically generate adaptation plans based solely on ADL models and an application problem description simplifies the specification and use of adaptation mechanisms for system architects. The approach uses a three-layer architecture that, while similar to previous work, provides several significant improvements. We apply our approach within the context of a mobile robotics case study.

An architecture-driven software mobility framework

Software architecture has been shown to provide an appropriate level of granularity for assessing a software systems quality attributes (e.g., performance and dependability). Similarly, previous research has adopted an architecture-centric approach to reasoning about and managing the run-time adaptation of software systems. For mobile and pervasive software systems, which are known to be innately dynamic and unpredictable, the ability to assess a systems quality attributes and manage its dynamic run-time behavior is especially important. In the past, researchers have argued that a software architecture-based approach can be instrumental in facilitating mobile computing. In this paper, we present an integrated architecture-driven framework for modeling, analysis, implementation, deployment, and run-time migration of software systems executing on distributed, mobile, heterogeneous computing platforms. In particular, we describe the frameworks support for dealing with the challenges posed by both logical and physical mobility. We also provide an overview of our experience with applying the framework to a family of distributed mobile robotics systems. This experience has verified our envisioned benefits of the approach, and has helped us to identify several avenues of future work.

Model driven middleware: A new paradigm for developing distributed real-time and embedded systems

Distributed real-time and embedded (DRE) systems have become critical in domains such as avionics (e.g., flight mission computers), telecommunications (e.g., wireless phone services), tele-medicine (e.g., robotic surgery), and defense applications (e.g., total ship computing environments). These types of system are increasingly interconnected via wireless and wireline networks to form systems of systems. A challenging requirement for these DRE systems involves supporting a diverse set of quality of service (QoS) properties, such as predictable latency/jitter, throughput guarantees, scalability, 24x7 availability, dependability, and security that must be satisfied simultaneously in real-time. Although increasing portions of DRE systems are based on QoS-enabled commercial-off-the-shelf (COTS) hardware and software components, the complexity of managing long lifecycles (often ~15-30 years) remains a key challenge for DRE developers and system integrators. For example, substantial time and effort is spent retrofitting DRE applications when the underlying COTS technology infrastructure changes. This paper provides two contributions that help improve the development, validation, and integration of DRE systems throughout their lifecycles. First, we illustrate the challenges in creating and deploying QoS-enabled component middleware-based DRE applications and describe our approach to resolving these challenges based on a new software paradigm called Model Driven Middleware (MDM), which combines model-based software development techniques with QoS-enabled component middleware to address key challenges faced by developers of DRE systems - particularly composition, integration, and assured QoS for end-to-end operations. Second, we describe the structure and functionality of CoSMIC (Component Synthesis using Model Integrated Computing), which is an MDM toolsuite that addresses key DRE application and middleware lifecycle challenges, including partitioning the components to use distributed resources effectively, validating software configurations, assuring multiple simultaneous QoS properties in real-time, and safeguarding against rapidly changing technology.

Architecture-driven self-adaptation and self-management in robotics systems

We describe an architecture-centric design and implementation approach for building self-adapting and self-managing robotics systems. The basis of our approach is the concept of meta-level components, which facilitate adaptation and management of application-level components. Our approach applies two key enhancements to the traditional usage of meta-level components: (1) we utilize three distinct, specialized meta-level components for the three fundamental activities of a robotics system: sensing, computation, and control, and (2) we allow meta-level components to themselves be monitored, managed and adapted by other (higher layer) meta-level components. In this way, our approach flexibly supports adaptive layered architectures of arbitrary depth, the specification of arbitrary system adaptation policies, and the provision of intelligent facilities for constructing adaptation plans on-the-fly. We showcase our approach using a team of autonomous mobile robots that engage in a leader-follower scenario and experience a wide variety of failures, activating distinct recovery mechanisms.

Scenario-driven dynamic analysis of distributed architectures

Software architecture constitutes a promising approach to the development of large-scale distributed systems, but architecture description languages (ADLs) and their associated architectural analysis techniques suffer from several important shortcomings. This paper presents a novel approach that reconceptualizes ADLs within the model-driven engineering (MDE) paradigm to address their shortcomings. Our approach combines extensible modeling languages based on architectural constructs with a model interpreter framework that enables rapid implementation of customized dynamic analyses at the architectural level. Our approach is demonstrated in XTEAM, a suite of ADL extensions and model transformation engines targeted specifically for highly distributed, resource-constrained, and mobile computing environments. XTEAM model transformations generate system simulations that provide a dynamic, scenario- and risk-driven view of the executing system. This information allows an architect to compare architectural alternatives and weigh trade-offs between multiple design goals, such as system performance, reliability, and resource consumption. XTEAM provides the extensibility to easily accommodate both new modeling language features and new architectural analyses.

Toward a Catalogue of Architectural Bad Smells

An architectural bad smell is a commonly (although not always intentionally) used set of architectural design decisions that negatively impacts system lifecycle properties, such as understandability, testability, extensibility, and reusability. In our previous short paper, we introduced the notion of architectural bad smells and outlined a few common smells. In this paper, we significantly expand upon that work. In particular, we describe in detail four representative architectural smells that emerged from reverse-engineering and re-engineering two large industrial systems and from our search through case studies in research literature. For each of the four architectural smells, we provide illustrative examples and demonstrate the smells impact on system lifecycle properties. Our experiences indicate the need to identify and catalog architectural smells so that software architects can discover and eliminate them from system designs.

Synthesizing partial component-level behavior models from system specifications

Initial system specifications, such as use-case scenarios and properties, only partially specify the future system. We posit that synthesizing partial component-level behavior models from these early specifications can improve software development practices. In this paper, we provide a novel algorithm for deriving a Modal Transition System (MTS) for individual system components from system-level scenario and property specifications. The generated MTSs capture the possible component implementations that (1) necessarily provide the behavior required by the scenarios, (2) restrict behavior forbidden by the properties, and (3) leave the behavior that is neither explicitly required nor forbidden as undefined. We also show how our algorithm helps to discover potential design flaws.

Model-Driven Configuration and Deployment of Component Middleware Publish/Subscribe Services

Quality of service (QoS)-enabled publish/subscribe services are available in component middleware platforms, such as the CORBA Component Model (CCM). Today, however, these platforms lack a simple and intuitive way to integrate publish/subscribe service configurations and deployments. This paper illustrates how generative model-driven techniques and tools can automate many service configuration and deployment tasks associated with integrating publish/subscribe services into QoS-enabled component-based systems. We evaluatethese techniques in the context of a real-time avionics mission computing problem involving a system with over 50 components. Our evaluation finds that an automated model-driven configuration of a reusable component middleware framework not only significantly reduces handwritten code and but also simultaneously achieves high reusability and composability of CCM components.

A Methodology and Framework for Creating Domain-Specific Development Infrastructures

Domain-specific architectures, middleware platforms, and analysis techniques leverage domain knowledge to help engineers build systems more effectively. An integrated set of these elements is called a domain-specific development infrastructure (DSDI). DSDIs are commonly created in a costly, ad-hoc fashion because current model-driven engineering (MDE) technologies lack sufficient mechanisms for capturing the semantics of domain concepts. In this paper, we propose a methodology for incorporating semantics within MDE frameworks to simplify and automate DSDI integration. We also present and evaluate a framework, called XTEAM, that implements our approach, resulting in structured processes and enforceable guidelines for DSDI integration. We have applied our approach to several DSDIs, and report on the benefits accrued.

CoDesign: a highly extensible collaborative software modeling framework

Large, multinational software development organizations face a number of issues in supporting software design and modeling by geographically distributed architects. To address these issues, we present CoDesign, an extensible, collaborative, event-based software modeling framework developed in a distributed, collaborative setting by our two organizations. CoDesigns core capabilities include real-time model synchronization between geographically distributed architects, as well as detection and resolution of a range of modeling conflicts via several off-the-shelf conflict detection engines.