Abdelkarim Erradi

SOAF: An Architectural Framework for Service Definition and Realization

Service oriented architecture (SOA) is an approach for building distributed systems that deliver application functionality as a set of self-contained business-aligned services with well-defined and discoverable interfaces. This paper presents a systematic and architecture-centric framework, named service oriented architecture framework (SOAF), to ease the definition, the design and the realization of SOA in order to achieve a better business and IT alignment. The proposed framework is business-process centric and comprises a set of structured activities grouped in five phases. It incorporates a range of techniques and guidelines for systematically identifying services, deciding service granularity and modeling services while integrating existing operational/legacy systems. The results from a pilot validation of SOAF for SOA enablement of a realistic securities trading application are presented. Best practices and lessons learned are also discussed

Policy-driven middleware for self-adaptation of web services compositions

We present our policy-based middleware, called Manageable and Adaptive Service Compositions (MASC), for dynamic self-adaptation of Web services compositions to various changes. MASC integrates and extends our earlier middleware called the Web Services Message Bus (wsBus). In particular, we discuss MASC support for customization of Web services compositions to address business exceptions and wsBus support for correction (fault management) of Web services compositions to improve reliability. We have evaluated the former support on a stock trading case study and the latter support on a supply chain management case study. Our solutions are complementary to the existing approaches and provide: coordination of fault management between SOAP messaging and business process orchestration, greater diversity of monitoring and control constructs, specification of both technical and business aspects used for adaptation decisions, higher level of abstraction easier for use by non-technical people, and externalization of monitoring and adaptation actions from definitions of business processes.

Recovery Policies for Enhancing Web Services Reliability

Web services are gaining acceptance as a standards-based approach for integrating loosely coupled services often distributed over a network. Hence, achieving high levels of reliability and availability in spite of service or infrastructure failures poses unique set of challenges. However, Web services middleware provide limited constructs for specifying faults detection and recovery actions. Additionally, faults-handling logic often gets scattered and tangled with the service logic. Consequently, this negatively impacts maintainability and adaptability. To address these requirements for reliable and fault tolerant Web services execution, we propose set extensible recovery policies to declaratively specify how to handle and recover from typical faults in Web services composition. The identified constructs were incorporated into a lightweight service management middleware named MASC (manageable and adaptive service composition) to transparently enact the fault management policies and facilitate the monitoring, configuration and control of managed services. Several experimental results with a service based supply chain management system illustrate the effectiveness of our approach to providing reliable and uninterrupted services

WS-Policy based Monitoring of Composite Web Services

MASC (Manageable and Adaptive Service Compositions)1* is a policy-based middleware for monitoring and control of composite Web services execution. The monitorable requirements are specified in the WS-Policy4MASC language that extends WS-Policy by defining new types of monitoring and control policy assertions. This paper focuses on MASC monitoring capabilities to detect business exceptions and runtime faults. Our solutions are complementary to the existing approaches and provide: synchronous and asynchronous monitoring both at the SOAP messaging layer and the process orchestration layer, greater diversity of monitoring and control constructs, as well as the externalization of monitoring and adaptation actions from definitions of business processes. We implemented a MASC proof-of-concept prototype and evaluated it on monitoring and adaptation scenarios from a stock trading case study. Our performance studies indicate that MASC overhead and scalability are acceptable.

A broker-based approach for improving Web services reliability

As Web services start to be deployed for mission-critical applications and for e-business scenarios, higher quality of service (QoS) and continuous service delivery become a critical issue to ensure high availability and reliability in spite of the failure or unavailability of the participating services or networks. These challenges call for vast improvements in the Web services containers and the mediation infrastructure. To address these requirements, we propose Web services message bus (wsBus), a lightweight service-oriented middleware for reliable and fault tolerant Web services interactions. This paper first discusses wsBus architecture and features and then it reports some experimental results to illustrate the effectiveness of wsBus in adding reliable and uninterrupted services to a supply chain management system.

MASC - .NET-Based Middleware for Adaptive Composite Web Services

MASC (manageable and adaptive service compositions) is a policy-based middleware for monitoring of Web service compositions and their dynamic adaptation to various runtime changes. MASC policies are described in our new WS-Policy extension called WS-Policy4MASC. Compared with recent related works, MASC has several distinctive characteristics, such as coordination of adaptation on the SOAP messaging layer and the business process orchestration layer, use of both technical and business metrics for adaptation decisions, and extending the power and flexibility of the new Microsoft .NET 3.0 platform. In this paper, we focus on MASC support for adaptation to address business exceptions and manage runtime faults. For example, a sub-process (or an activity) can be added, deleted, replaced, skipped, or retried. We have been implementing a MASC proof-of-concept prototype and evaluating it on adaptation scenarios from a stock trading case study. Our performance studies of the prototype indicate that overheads introduced by MASC are acceptable.

Differential QoS support in Web Services Management

The variation of contexts in which a Web service could be used and the resulting variation in quality of service (QoS) expectations makes a clear case for further research to extend Web services management platforms with more sophisticated control mechanisms to cater for differentiated service offerings. However, most Web services platforms are based on a best-effort model, which treats all requests uniformly, without any type of service differentiation or prioritization. This paper presents WS-DiffServ, a service differentiation middleware based on prioritization which leverages service requestor profile to classify service requests. We first explore the typical generic requirements of a differential QoS support in Web services management. We then present in detail the design of a priority based differentiated responsiveness platform for Web services

wsBus: QoS-aware middleware for reliable Web services interactions

Service-oriented architecture (SOA) using Web services is considered as the state-of-the-art for distributed systems integration. As Web services start to be deployed across enterprise boundaries and for collaborative e-business scenarios, higher quality of service (QoS) and reliable inter-application messaging becomes a critical issue to ensure guaranteed and ordered delivery even in the case of system or network failures or temporary service outage. To address these requirements, we propose wsBus, a lightweight service-oriented middleware for dependable Web services interactions using broker pattern. We discuss the system architecture and features then report our experiences in building wsBus as well as some initial performance results.

Service Design Process for Reusable Services: Financial Services Case Study

Service-oriented Architecture (SOA) is an approach for building distributed systems that deliver application functionality as a set of business-aligned services with well-defined and discoverable contracts. This paper presents typical a service design process along with a set of service design principles and guidelines for systematically identifying services, designing them and deciding the service granularity and layering. The advocated principles stem from our experiences in designing services for a realistic Securities Trading application. Best practices and lessons learned during this exercise are also discussed.

WS-Policy4MASC - A WS-Policy Extension Used in the MASC Middleware

WS-Policy4MASC is a new XML language that we developed for specification of monitoring and control (particularly, adaptation) policies in the Manageable and Adaptable Services Compositions (MASC) middleware. It extends the Web Services Policy Framework (WS-Policy) by defining new types of policy assertions. Goal policy assertions specify requirements and guarantees to be met in desired normal operation. Action policy assertions specify actions to be taken if certain conditions are met or not met. Utility policy assertions specify monetary values assigned to particular situations. Meta-policy assertions are used to specify which action policy assertions are alternatives and which business value-driven conflict resolution strategy should be used. WS- Policy4MASC also enables detailed specification of additional information necessary for run-time policy-driven management. We evaluated feasibility of the WS- Policy4MASC solutions by implementing a policy repository and other modules in MASC. We examined their usefulness on a set of realistic scenarios.