Dependability Assessment of Service-Oriented Architectures Using Fault Injection

Dependability assessment is an important aspect of any software system and shows the degree of trust and quality of service that is delivered by a system. Validation and verification techniques commonly employed to ensure that systems are fit for use attempt to remove all faults so that error conditions cannot occur but since it is not feasible to verify all states a system can achieve, it is not possible to completely test a system. Conversely, dependability assumes that failures may occur in a system and that mechanisms exist to mitigate any failures and thus provide a trustworthy system. This chapter discusses the different issues associated with dependability. The different techniques that can be used to assess dependability are discussed and are related to Service Orientated Architectures. A number of cases studies are used to show the practicality of the techniques used.

Design and Deployment of Service Oriented Applications with Non-Functional Requirements

As the use of SOA became a mainstream in enterprise application development, there is a growing need for designing non-functional aspects of service integration at the architectural level, instead of creating only technology specific assets (configuration descriptors). This architectural design supports flexibility and early validation of requirements. This chapter presents a model-driven method supporting the automated deployment of service configurations. This deployment technique is supported by an extensible tool chain where (i) service models are captured by a service-oriented extension of UML enabling to capture non-functional requirements, and (ii) configuration descriptors for the target deployment platform are derived by automated model transformations within the VIATRA2 framework.

Selective Querying for Adapting Hierarchical Web Service Compositions

Web Service compositions (WSC) often operate in volatile environments where the parameters of the component services change during execution. To remain optimal, the WSC could adapt to these changes by querying the participating providers for their revised parameters. Previously, the value of changed information (VOC) has been utilized in simple WSCs to selectively query only those services whose revised parameters are expected to bring about significant changes in the composition. In many cases, however, in order to promote scalability, a WSC is formulated as a more complex, nested structure – a higher-level WSC may be composed of WSs and lower-level WSCs – inducing a natural hierarchy over the composition. This chapter presents a novel approach that extends the capabilities of VOC-driven querying to address the problem of adapting hierarchical WSCs. It shows how to compose and adapt hierarchical WSCs by first deriving a model of volatility for lower-level WSCs and then by descending down the levels of nesting and computing the VOC for WSCs at each level. Experimental results demonstrate that this approach provides an effective and efficient solution for complex, hierarchical WSCs.

Quality of Service Monitoring, Diagnosis, and Adaptation for Service Level Management

A key requirement in Service Level Management (SLM) is managing the Quality of Services (QoS) demanded by clients and offered by providers. This managing process is complicated by the globalization and Internet scale of enterprise services and their compositions. This chapter presents two contributions to the QoS management task for SLM. First, instead of considering monitoring as an isolated service, it incorporates a monitoring service as an integral part of a comprehensive QoS management framework for SLM. Second, it includes a diagnosis service as an integral part of the QoS management framework. Using the data fed from monitoring service, diagnosis service detects system condition changes and reasons about the causes of detected degradation in networked enterprise system. With condition detection and situation understanding, the QoS management framework can then proactively activate adaptation mechanisms to maximize the system’s ability to meet QoS contract requirements of concurrent clients. Using this framework, enterprise systems can provide real time automated QoS management to optimize system resources in meeting contract requirements. This approach is validated using QoS management services integrated in a publish/subscribe style of SOA. Benefits of QoS monitoring, diagnosis, and adaptation services for responsiveness SLM are demonstrated via experiments.

Design of Quality Aspects in Service Oriented Architecture through Service Level Agreements

This chapter gives a solution to design Service Oriented Architectures which defines and manages Service Level Agreements to enforce Quality of Services and achieves adaptivity at runtime. The validation of this proposed approach is performed through an actual case study in the context of the multimedia application domain.

Web Services Composition Problem

In the approach taken in this chapter, the composition problem is as follows: given a client service, a goal service and a set of available services, determine if there exists a mediator service that enables the communication between the client and the existing services in order to satisfy the client request, represented by the goal service. In this chapter’s model, available services that have access control constraints are considered. To formally capture these constraints, the chapter defines Web Services as Conditional Communicating Automata (CCA) in which communication is done through bounded ports. This chapter gives a detailed presentation of said model and gives complexity results of the composition problem.

Specification of Non-functional Requirements and Their Trade-offs in Service Contracts in the NGOSS Framework

The community of Operation Support Systems (OSS) for telecom applications defined a set of fundamental principles, processes, and architectures for developing the Next Generation OSS through the TeleManagement Forum TMF. At the heart of NGOSS lies the notion of a “Contract” which embodies the specification of services offered by an OSS component for quality management and product evaluation. However, TMF does not provide any method (or process) for specification of the non-functional part in the NGOSS contract specification. This chapter develops a systematic approach for specifying non-functional requirements of telecom OSS applications for contracts in the NGOSS framework for quality management and evaluation. Specifically, two categories of non-functional specification techniques are explored: qualitative and quantitative. Furthermore, two quantitative non-functional requirements specification methods are introduced: crisp and elastic to expand the capability of the current NGOSS contract specification method since only qualitative non-functional specification is currently available from TMF. In addition, a technique is developed for specification of trade-offs between non-functional requirements.

Adding Semantics to QoS Requirements

To lead the software-service revolution and to make real the promise of Business to Business interactions, QoS and Semantics play key roles in every phase of Web processes’ life-cycle. Ontology-based approaches for specifying QoS enable machines to reason autonomously and dynamically on QoS knowledge, aiding the development of open and large-scale distributed applications. This chapter presents the impact of Semantics for the management of QoS Requirements in Service-based Applications, focusing on the onQoS ontology, its role for specifying service requirements and to support queries for service discovery through the onQoS-QL language. The introduced concepts and the results presented in the chapter pave the way to new technology horizons where the semantics could represent the global glue for Web processes.

Complexity Analysis at Design Stages of Service Oriented Architectures as a Measure of Reliability Risks

Tremendous growth in interest of Service oriented Architectures (SOA) triggers a substantial amount of research in its reliability assurances. To minimize the risks of these types of systems’ failure, it is a requirement to flag those components of SOA that are likely to have higher faults. Clearly, the degree of protection or prevention of faults mechanism is not same for all components. This chapter proposes the usage of metrics that are simply heuristics and are used to scan the system model and flag complex components where faults are more likely to take place. Thus the metric output is some priority or it is a measure of likelihood of faults in a component. This chapter then suggests the designers for possible changes in the design if there remains any risk(s) of degradation of desired functionalities.

Applying Concept Reuse for Adaptive Service Composition

Web Services are gaining acceptance as the predominant standards-based approach to building open distributed systems. Business Process Execution Language (BPEL) allows for the composition of existing Web Services to create higher-level Web Services. There is a need to deliver reliable service compositions with precise Quality of Service (QoS) attributes covering functional correctness, performance and dependability, especially since the current BPEL standard provides limited constructs for specifying exceptional behavior and recovery actions. This chapter presents a language-based approach to transparently adapting BPEL processes to improve reliability. This approach addresses reliability at the business process layer (i.e., the language layer) using a code generator, which weaves fault-tolerant code to the original code and an external proxy. The chapter also explains the software patterns present in this approach. These patterns constitute abstract reusable concepts that will facilitate rapid model-driven development of adaptive service compositions that can be easily configured for a range of situations.