João Pedro Sousa

Aura: an Architectural Framework for User Mobility in Ubiquitous Computing Environments

Ubiquitous computing poses a number of challenges for software architecture. One of the most important is the ability to design software systems that ac- commodate dynamically-changing resources. Resource variability arises natu- rally in a ubiquitous computing setting through user mobility (a user moves from one computing environment to another), and through the need to exploit time-varying resources in a given environment (such as wireless bandwidth). Traditional approaches to handling resource variability in applications attempt to address the problem by imposing uniformity on the environment. We argue that those approaches are inadequate, and describe an alternative architectural framework that is better matched to the needs of ubiquitous computing. A key feature of the architecture is that user tasks become first class entities. User proxies, or Auras, use models of user tasks to set up, monitor and adapt com- puting environments proactively. The architectural framework has been im- plemented and is currently being used as a central component of Project Aura, a campus-wide ubiquitous computing effort.

Software Engineering for Self-Adaptive Systems: A Second Research Roadmap

The goal of this roadmap paper is to summarize the state-of-the-art and identify research challenges when developing, deploying and managing self-adaptive software systems. Instead of dealing with a wide range of topics associated with the field, we focus on four essential topics of self-adaptation: design space for self-adaptive solutions, software engineering processes for self-adaptive systems, from centralized to decentralized control, and practical run-time verification & validation for self-adaptive systems. For each topic, we present an overview, suggest future directions, and focus on selected challenges. This paper complements and extends a previous roadmap on software engineering for self-adaptive systems published in 2009 covering a different set of topics, and reflecting in part on the previous paper. This roadmap is one of the many results of the Dagstuhl Seminar 10431 on Software Engineering for Self-Adaptive Systems, which took place in October 2010.

Task-based adaptation for ubiquitous computing

An important domain for autonomic systems is the area of ubiquitous computing: users are increasingly surrounded by technology that is heterogeneous, pervasive, and variable. In this paper we describe our work in developing self-adapting computing infrastructure that automates the configuration and reconfiguration of such environments. Focusing on the engineering issues of self-adaptation in the presence of heterogeneous platforms, legacy applications, mobile users, and resource variable environments, we describe a new approach based on the following key ideas: 1) explicit representation of user tasks allows us to determine what service qualities are required of a given configuration; 2) decoupling task and preference specification from the lower level mechanisms that carry out those preferences provides a clean engineering separation of concerns between what is needed and how it is carried out; and 3) efficient algorithms allow us to calculate in real time near-optimal resource allocations and reallocations for a given task

Dynamic configuration of resource-aware services

An important emerging requirement for computing systems is the ability to adapt at run time, taking advantage of local computing devices, and coping with dynamically changing resources. Three specific technical challenges in satisfying this requirement are to (1) select an appropriate set of applications or services to carry out a users task, (2) allocate (possibly scarce) resources among those applications, and (3) reconfigure the applications or resource assignments if the situation changes. In this paper, we show how to provide a shared infrastructure that automates configuration decisions given a specification of the users task. The heart of the approach is an analytical model and an efficient algorithm that can be used at run time to make near-optimal (re)configuration decisions. We validate this approach both analytically and by applying it to a representative scenario.

Software Architecture-Based Adaptation for Pervasive Systems

An important requirement for pervasive computing systems is the ability to adapt at runtime to handle varying resources, user mobility, changing user needs, and system faults. In this paper we describe an approach in which dynamic adaptation is supported by the use of software architectural models to monitor an application and guide dynamic changes to it. The use of externalized models permits one to make reconfiguration decisions based on a global perspective of the running system, apply analytic models to determine correct repair strategies, and gauge the effectiveness of repair through continuous system monitoring. We illustrate the application of this idea to pervasive computing systems, focusing on the need to adapt based on performance-related criteria and models.

SASSY: A Framework for Self-Architecting Service-Oriented Systems

Making architectural decisions manually in the presence of quality-of-service trade-offs can be complicated. The SASSY (Self-architecting Software Systems) framework automatically generates candidate software architectures and selects the one that best serves stakeholder-defined, scenario-based quality-of-service (QoS) goals. This lets domain experts concentrate on functional and QoS requirements. SASSY reduces the effort of composing service-oriented systems by automatically generating the QoS-optimized architecture and rapidly reconfiguring it at runtime. Self-architecting occurs during initial system deployment and at runtime, thus making systems self-adaptive, self-healing, self-managing, and self-optimizing.

A framework for utility-based service oriented design in SASSY

The architecture of a software system has a significant impact on its quality of service (QoS) as measured by several performance metrics such as execution time, availability, throughput, and security. This paper presents a framework that is part of a large project called SASSY (Self-Architecting Software Systems), whose goal is to allow domain experts to specify the system requirements using a visual activity-based language. The SASSY framework automatically generates a base architecture that corresponds to the requirements. Then SASSY generates a new architecture, derived from the base architecture, that optimizes a utility function for the entire system. The utility function is a multivariate function of several QoS metrics. The paper shows a complete example and illustrates how SASSY automatically adapts to changes in the environments QoS features.

Using Architectural Style as a Basis for System Self-repair

An increasingly important requirement for software systems is the capability to adapt at run time in order to accommodate varying resources, system errors, and changing requirements. For such self-repairing systems, one of the hard problems is determining when a change is needed, and knowing what kind of adaptation is required. Recently several researchers have explored the possibility of using architectural models as a basis for run time monitoring, error detection, and repair. Each of these efforts, however, has demonstrated the feasibility of using architectural models in the context of a specific style. In this paper we show how to generalize these solutions by making architectural style a parameter in the monitoring/repair framework and its supporting infrastructure. The value of this generalization is that it allows one to tailor monitoring/repair mechanisms to match both the properties of interest (such as performance or security), and the available operators for run time adaptation.

Towards Practical Runtime Verification and Validation of Self-Adaptive Software Systems

Software validation and verification (VV and (ii) present a proposal for including V&V operations explicitly in feedback loops for ensuring the achievement of software self-adaptation goals. Both of these contributions provide valuable starting points for V&V researchers to help advance this field.

A Modeling Language for Activity-Oriented Composition of Service-Oriented Software Systems

The proliferation of smart spaces and emergence of new standards, such as Web Services, have paved the way for a new breed of software systems. Often the complete functional and QoS requirements of such software systems are not known a priori at design-time, and even if they are, they may change at run-time. Unfortunately, the majority of existing software engineering techniques rely heavily on human reasoning and manual intervention, making them inapplicable for automatic composition of such software systems at run-time. Moreover, these approaches are primarily intended to be used by technically knowledgeable software engineers, as opposed to domain users. In this paper, we present Service Activity Schemas (SAS) , an activity-oriented language for modeling software systems functional and QoS requirements. SAS targets service-oriented software systems, and relies on an ontology to provide domain experts with modeling constructs that are intuitively understood. SAS forms the centerpiece of a framework intended for user-driven composition and adaptation of service-oriented software systems in a pervasive setting. We provide a detailed description of SAS in the context of a case study and formally specify its structural and dynamic properties.