Vladimir Tosic

Management applications of the web service offerings language (WSOL)

We discuss Web Service Management (WSM) and Web Service Composition Management (WSCM) applications of the Web Service Offerings Language (WSOL) and how the language supports these applications. WSOL is a language for the formal specification of classes of service, various constraints (functional constraints, Quality of Service QoS, and access rights), and management statements (prices, monetary penalties, and management responsibilities) for Web Services. Describing a Web Service in WSOL, in addition to the Web Services Description Language, enables monitoring, metering, accounting, and management of Web Services. Metering of QoS metrics and evaluation of constraints can be the responsibility of the provider Web Service, the consumer, and/or one or more mutually trusted third parties (SOAP intermediaries or probes). Further, manipulation (switching, deactivation, reactivation, deletion, or creation) of classes of service can be used for dynamic (run-time) adaptation and management of Web Service compositions. To demonstrate the usefulness of WSOL for WSM and WSCM, we have developed a corresponding management infrastructure, the Web Service Offerings Infrastructure (WSOI). WSOI enables monitoring of WSOL-enabled Web Services and dynamic manipulation of their classes of service.

WSOL - Web Service Offerings Language

WSOL (Web Service Offerings Language) is an XML (Extensible Markup Language) notation compatible with the WSDL (Web Services Description Language) standard. While WSDL is used for describing operations provided by Web Services, WSOL enables formal specification of multiple classes of service for one Web Service. A service offering is a formal representation of one class of service for a Web Service. As classes of service for Web Services are determined by combinations of various constraints, WSOL enables formal specification of functional constraints, some QoS (a.k.a., non-functional) constraints, simple access rights (for differentiation of service), price, and relationships with other service offerings of the same Web Service. Describing a Web Service in WSOL, in addition to WSDL, enables selection of a more appropriate Web Service and service offering for particular circumstances. Further, it supports dynamic adaptation and management of Web Service compositions using manipulation of service offerings.

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

On Requirements for Ontologies in Management of Web Services

Formal specification of various constraints, including quality of service (QoS) and price, is very important for successful dynamic (i.e., runtime) composition of Web Services. For specification of these constraints, it is important to formally define QoS metrics, measurement units, and currency units used. Ontologies provide a mechanism for such formal definition. In this paper we discuss some requirements for ontologies that can be used in representing QoS constraints and in management of Web Services, with special focus on QoS metrics, measurement units, and currency units. Particularly, we emphasize the need for the formal representation of dependencies and relationships between QoS metrics, even when such information seems redundant. Our study of existing ontologies showed that they need further work to satisfy our requirements. We also state the need for independent, third-party Web Services for ontological translations between different QoS metrics, measurement units, and currencies.

Web Service Offerings Infrastructure (WSOI) - a management infrastructure for XML Web services

Our Web Service Offerings Language (WSOL) enables formal specification of important management information - classes of service (modeled as service offerings), various types of constraint (functional, QoS, access rights), and management statements (e.g., prices, penalties, and management responsibilities) - for XML (Extensible Markup Language) Web services. To demonstrate the usefulness of WSOL for the management of Web services and their compositions, we have developed a corresponding management infrastructure, the Web Service Offerings Infrastructure (WSOI). WSOI enables monitoring and accounting of WSOL service offerings and their dynamic manipulation. To support monitoring of WSOL service offerings, we have extended the Apache Axis open-source SOAP engine with WSOI-specific modules, data structures, and management ports. To support dynamic manipulation of WSOL service offerings, we have developed appropriate algorithms, protocols, and management port types and built into WSOI modules and data structures for their implementation. Apart from provisioning of WSOL-enabled Web services, we are using WSOI to perform experiments comparing dynamic manipulation of WSOL service offerings and alternatives.

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.

On comprehensive contractual descriptions of Web services

Comprehensive contractual description of Web services and Web service compositions is needed for selection of appropriate Web services and their service and quality of service (QoS) levels, for monitoring of operation of Web services, and for management of Web services and Web service compositions. We systematically examined what types of technical contracts are useful for Web services and Web service compositions and classified them into three broad categories (functional, quality, and infrastructure contracts), each containing several contract types. Our study of how prominent Web service languages can or cannot be used for specification of these contract types shows that they enable specification of only particular types of contracts, sometimes even in incompatible ways. Consequently, we advocate a unified framework for comprehensive contractual description of Web services and Web service compositions. At the end, we outline one possible approach to comprehensive contractual description, based on extending existing Web service technologies.

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.

Towards a Web service composition management framework

We suggest that the composition of Web services is an activity that needs to be managed, and that Web service composition management is distinct from the management of individual Web services. We describe a set of requirements to help make this distinction. The four main groups of these requirements are: service discovery, service selection and contract formation, composition verification, composition management. Then, we discuss architectural alternatives (centralized, federated, and peer-to-peer) for a Web service composition management framework.