Enhancing Planning-Based Adaptation Middleware with Support for Dependability: a Case Study

Recent evolutions of mobile devices have opened up for new opportunities for building advanced mobile applications. In particular, these applications are capable of discovering and exploiting software and hardware resources that are made available in their environment. A possible approach for supporting these ubiquitous interactions consists in adapting the mobile application to reflect the functionalities that are provided by the environment. However, these approaches often fail in offering a sufficient degree of resilience to potential device, network, and software failures, which are particularly frequent in ubiquitous environments. Therefore, the contribution of this paper is to integrate the dependability concern in the process of mobile applications adaptation. In particular, we propose to reflect dependability mechanisms as alternative configurations for a given application. This reflection allows the planning-based adaptation middleware to automatically decide, based on contextual information, to enable the support for dependability or not

Resource Aware Run-Time Adaptation Support for Recovery Strategies

The selection of recovery strategies is often based only on the types and circumstances of the failures. However, also changes in the environment such as fewer resources at node levels or degradation of quality-of-service should be considered before allocating a new process/task to another host or before taking reconfiguration decisions. In this paper we present why and how resource availability information should be considered for recovery strategies adaptation. Such resource aware run-time adaptation of recovery improves the availability and survivability of a system

Context constraint integration and validation in dynamic web service compositions

System architectures that cross organisational boundaries are usually implemented based on Web service technologies due to their inherent interoperability benets. With increasing exibility requirements, such as on-demand service provision, a dynamic approach to service architecture focussing on composition at runtime is needed. The possibility of technical faults, but also violations of functional and semantic constraints require a comprehensive notion of context that captures composition-relevant aspects. Context-aware techniques are consequently required to support constraint validation for dynamic service composition. We present techniques to respond to problems occurring during the execution of dynamically composed Web services implemented in WS-BPEL. A notion of context { covering physical and contractual faults and violations { is used to safeguard composed service executions dynamically. Our aim is to present an architectural framework from an application-oriented perspective, addressing practical considerations of a technical framework

Extended Fault Taxonomy of SOA-Based Systems

Service Oriented Architecture (SOA) is considered as a standard for enterprise software development. The main characteristics of SOA are dynamic discovery and composition of software services in a heterogeneous environment. These properties pose newer challenges in fault management of SOA-based systems (SBS). A proper understanding of different faults in an SBS is very necessary for effective fault handling. A comprehensive three-fold fault taxonomy is presented here that covers distributed, SOA specific and non-functional faults in a holistic manner. A comprehensive fault taxonomy is a key starting point for providing techniques and methods for accessing the quality of a given system. In this paper, an attempt has been made to outline several SBSs faults into a well-structured taxonomy that may assist developers to plan suitable fault repairing strategies. Some commonly emphasized fault recovery strategies are also discussed. Some challenges that may occur during fault handling of SBSs are also mentioned

Dynamic Checkpointing of Composite Web Services

Web services provide services to their consumers in accordance with terms and conditions laid down in a document called as Service Level Agreement (SLA). Web services have to abide by these terms and conditions failing which, SLA faults result. Fault handling of web services is a key mechanism using which SLA faults can be avoided. We propose fault handling of choreographed web services using checkpointing and recovery. We propose checkpointing in three stages: design, deployment and dynamic checkpointing. We have presented first two stages of checkpointing in our earlier publications. In this paper we discuss the need for dynamic checkpointing and, various factors to be considered while revising checkpoint locations dynamically. We also propose a framework for implementing dynamic checkpointing