Publications in Web Services

Articles in Refereed Journals:

1. L. Baresi, D. Bianculli, C. Ghezzi, S. Guinea, P. Spoletini. Validation of web service compositions. IET Software, Vol. 1, Num. 6, pages 219-232, December 2007.
   Abstract: Web services support software architectures that can evolve dynamically. In particular, in this paper the focus is on architectures where services are composed (orchestrated) through a workflow described in the business process execution language (BPEL). It is assumed that the resulting composite service refers to external services through assertions that specify their expected functional and non-functional properties. On the basis of these assertions, the composite service may be verified at design time by checking that it ensures certain relevant properties. Because of the dynamic nature of web services and the multiple stakeholders involved in their provision, however, the external services may evolve dynamically, and even unexpectedly. They may become inconsistent with respect to the assertions against which the workflow was verified during development. As a consequence, validation of the composition must extend to run time. In this work, an assertion language, called assertion language for BPEL process interactions (ALBERT), is introduced; it can be used to specify both functional and non-functional properties. An environment which supports design-time verification of ALBERT assertions for BPEL workflows via model checking is also described. At run time, the assertions can be turned into checks that a software monitor performs on the composite system to verify that it continues to guarantee its required properties. A TeleAssistance application is provided as a running example to illustrate our validation framework.

2. Roberto Lucchi, Manuel Mazzara. A pi-calculus based semantics for WS-BPEL . Journal of Logic and Algebraic Programming, Vol. 70, Num. 1, pages 96-118, January 2007.
   Abstract: Recently, the term Web services orchestration has been introduced to address some issues related to Web services composition, that is the way of defining a complex service out of simpler ones. Several proposals for describing orchestration for business processes have been presented in the last years and many of these languages make use of concepts as long-running transactions and compensations for coping with error handling. WS-BPEL 2.0, the most credited candidate for becoming a standard, provides three different mechanisms allowing to cope with abnormal situations: exception, event and compensation handling. This complexity makes it difficult to formally define the framework, thus limiting the formal reasoning about the designed applications. In this paper we advocate that three different mechanisms for error handling are not necessary and we formalize a novel orchestration language based on the idea of event notification as the unique error handling mechanism. To this end, we formally define the three BPEL mechanisms in terms of our calculus. It is possible to take advantages of this formal description in two ways. Firstly, this language represents by itself a proposal of simplification for WS-BPEL 2.0 including an unambiguous specification. Secondly, an implementor of an actual WS-BPEL 2.0 orchestration engine could implement simply this single mechanism providing all the remaining ones by compilation. With this attempt we intend to give a concrete contribute towards the improvement of the quality of the BPEL specification, the applicability of BPEL itself and the implementation of real orchestration engines. Finally, as a case study we consider some of the hundreds of open issues met by the WS-BPEL designers and we propose a solution making use of the experience gained developing our algebra.

3. D. Ardagna, M. Comuzzi, E. Mussi, B. Pernici, P. Plebani. PAWS: A Framework for Executing Adaptive Web-Service Processes. IEEE Software, To Appear, 2007.
   Abstract: The processes with adaptive Web services framework couples design-time and runtime mechanisms to flexibly and adoptively execute managed Web-services-based business processes.

4. Mike P. Papazoglou, Benedikt Kratz. Web services technology in support of business transactions. Service Oriented Computing and Applications, Vol. 1, Num. 1, pages 51-63, 2007.
   Abstract: Advanced business applications typically involve well-defined business functions such as payment processing, shipping and tracking, determining new product offerings, granting/extending credit, managing market risk and so on. These reflect commonly standard business functions that apply to a variety of application scenarios. Although such business functions drive transactional applications between trading partners they are completely external to current Web services transaction mechanisms and are only expressed as part of application logic. To remedy this situation, this paper proposes a business-aware Web services transaction model and support mechanisms, which is driven by common business functions. The model allows expressing business functions such as payment and credit conditions, delivery conditions, business agreements stipulated in SLAs, liabilities and dispute resolution policies. It allows blending these business functions with QoS criteria such as security support to guarantee integrity of information, confidentiality, and non-repudiation.

5. Ma, K.J.. Web services: what's real and what's not?. IT Professional, Vol. 7, Num. 2, pages 14-21, March 2005.
   Abstract: The idea of abstracted, well-defined, and ubiquitously invokable services replacing proprietary interprocess communications has been a goal of system designers for a long time. The rise of Web services has led to a lot of misconceptions about how they can and cannot support the holy grail of a service-oriented architecture (SOA). This article seeks to put Web services in perspective, explaining their current capabilities and what industry can expect from them in the near term. It gives an overview of how technologies such as the Extensible Markup Language (XML), XML schemas, Extensible Stylesheet Language Transformations (XSLT), the Simple Object Access Protocol (SOAP), the Web Services Description Language (WSDL), and universal description, discovery, and integration (UDDI) fit into the equation for an SOA.

6. James Pasley. How BPEL and SOA Are Changing Web Services Development. IEEE Internet Computing, Vol. 9, Num. 3, pages 60-67, 2005.
   Abstract: As the use of Web services grows, organizations are increasingly choosing the Business Process Execution Language for modeling business processes within the Web services architecture. In addition to orchestrating organizations' Web services, BPEL's strengths include asynchronous message handling, reliability, and recovery. By developing Web services with BPEL in mind, organizations can implement aspects of the service-oriented architecture that might previously have been difficult to achieve.

7. Neal Leavitt. Are Web Services Finally Ready to Deliver?. IEEE Computer, Vol. 37, Num. 11, pages 14-18, November 2004.
   Abstract: Web services, in brief, are a framework of software technologies designed to support interoperable machine-to-machine interaction over a network. Companies on different systems can use Web services to exchange information online with business partners, customers, and suppliers. Various standards organizations and industry consortia are developing Web services specifications without a unifying authority. Organizations such as the World Wide Web Consortium (W3C), the Organization for the Advancement of Structured Information Standards (OASIS), the Liberty Alliance Project, and the Web Services Interoperability Organization (WS-I) have developed or reviewed numerous standards. A primary goal of Web services is to unlock a new generation of e-commerce applications.

8. Alexander Keller, Heiko Ludwig. The WSLA Framework: Specifying and Monitoring Service Level Agreements for Web Services. J. Network Syst. Manage., Vol. 11, Num. 1, 2003.
   Abstract: We describe a novel framework for specifying and monitoring Service Level Agreements (SLA) for Web Services. SLA monitoring and enforcement becomes increasingly important in a Web Service environment where enterprises rely on services that may be subscribed dynamically and on demand. For economic and practical reasons, we want an automated provisioning process for both the service itself as well as the SLA management system. It measures and monitors the QoS parameters, checks the agreed-upon service levels, and reports violations to the authorized parties involved in the SLA management process. The Web Service Level Agreement (WSLA) framework, our approach to these issues, is targeted at defining and monitoring SLAs for Web Services. Although WSLA has been designed for a Web Services environment, it is applicable as well to any inter-domain management scenario such as business process and service management or the management of networks, systems and applications in general. The WSLA framework consists of a flexible and extensible language based on XML Schema and a runtime architecture comprising several SLA monitoring services, which may be outsourced to third parties to ensure a maximum of accuracy. WSLA enables service customers and providers to unambiguously define a wide variety of SLAs, specify the SLA parameters and the way how they are measured, and relate them to managed resource instrumentations. Upon receipt of an SLA specification, the WSLA monitoring services are automatically configured to enforce the SLA. An implementation of the WSLA framework, the SLA Compliance Monitor, is publicly available as part of the IBM Web Services Toolkit.

Articles in Refereed Conferences:

1. Fabio Barbon, Paolo Traverso, Marco Pistore, Michele Trainotti. Run-Time Monitoring of Instances and Classes of Web Service Compositions. ICWS, pages 63-71, 2006.
   Abstract: The run-time monitoring of web service compositions has been widely acknowledged as a significant and challenging problem. In this paper, we propose a novel solution to the problem of monitoring web services implemented in BPEL. We devise an architecture that clearly separates the business logic of a web service from its monitoring functionality. The architecture supports both "instance monitors" that deal with the execution of a single instance of BPEL process, as well as "class monitors" that report aggregated information about all the instances of a BPEL process. We also define a language for the specification of instance and class monitors. The language allows for specifying boolean, statistic, and time-related properties. Finally, we devise a technique for the automatic translation of all these kinds of monitors to Java programs.

2. Dimka Karastoyanova, Alejandro Houspanossian, Mariano Cilia, Frank Leymann, Alejandro P. Buchmann. Extending BPEL for Run Time Adaptability. EDOC, pages 15-26, 2005.
   Abstract: The existing Web Service Flow (WS-flow) technologies enable both static and dynamic binding of participating Web services (WSs) on the process model level. Adaptability on per-instance basis is not sufficiently supported and therefore must be addressed to improve process flexibility upon changes in the environment. Ad-hoc process instance changes can be enabled by swapping participating WS instances, by modifying port Types of the partners to be invoked, and by changing process logic. In this work we address the problem of dynamic binding of WSs to WS-flow instances at run time, i.e. the ability to exchange a WS instance participating in a WS-flow instance with an alternative one. The problem is additionally complicated by the fact that the execution of a process depends on its deployment. We describe the "find and bind" mechanism, and we show its representation as a BPEL extension. We discuss the benefits that could be gained and the disadvantages it brings in. The mechanism extends and improves the existing process technologies. It facilitates a precisely controlled policy-based selection of WSs at run time and also provides for process instance repair, while maintaining simplicity. We also discuss a prototypical implementation of the presented functionality.

3. Khaled Mahbub, George Spanoudakis. Run-time Monitoring of Requirements for Systems Composed of Web-Services: Initial Implementation and Evaluation Experience. ICWS, pages 257-265, 2005.
   Abstract: This paper describes a framework supporting the runtime monitoring of requirements for systems implemented as compositions of Web-services specified in BPEL. The requirements that can be monitored are specified in event calculus. The paper presents an overview of the framework and describes the architecture and implementation of a tool that we have developed to operationalise it. It also presents the results of a preliminary experimental evaluation of the framework.

4. Vladimir Tosic, Bernard Pagurek, Kruti Patel. WSOL - A Language for the Formal Specification of Classes of Service for Web Services. ICWS, pages 375-381, 2003.
   Abstract: We are developing a language, Web Service Offerings Language (WSOL), for the formal specification of various constraints, management statements, and classes of service for Web Services. WSOL is an XML (Extensible Markup Language) notation compatible with WSDL (Web Services Description Language). A service offering in WSOL is a formal description of one class of service of a Web Service. It contains formal representation of various constraints: functional (pre-, post-, and future- conditions), Quality of Service (QoS, a.k.a. non-functional, extra- functional), and access rights. It also contains management statements, such as statements about prices, monetary penalties, and management responsibilities. One Web Service can be associated with multiple service offerings. For easier specification of similar service offerings, WSOL enables specification of constraint groups (CGs) and constraint group templates (CGTs). We have also developed a format for representation of dynamic relationships between service offerings. WSOL service offerings are simple contracts and SLAs (Service Level Agreements) between Web Services. Describing a Web Service in WSOL, in addition to WSDL, enables monitoring, metering, and management of Web Services. The Web Service, its consumer, or one or more designated third parties (usually SOAP message intermediaries) can meter QoS metrics and evaluate constraints in WSOL service offerings. Further, manipulation of service offerings can be used for dynamic adaptation and management of Web Service compositions. In addition, WSOL supports selection of a more appropriate Web Service and service offering for particular circumstances. The main distinctive characteristics of WSOL, compared to recent related works, are its expressive power, features that reduce run-time overhead, and orientation towards management applications.

Technical Reports and Manuals:

1. Siddharth Bajaj, Don Box, Dave Chappell, Francisco Curbera, Glen Daniels, Phillip Hallam-Baker, Maryann Hondo, Chris Kaler, Dave Langworthy, Anthony Nadalin, Nataraj Nagaratnam, Hemma Prafullchandra, Claus von Riegen, Daniel Roth, Jeffrey Schlimmer, Chris Sharp, John Shewchuk, Asir Vedamuthu, Ümit Yalcinalp, David Orchard . Web Services Policy Framework (WS- Policy). IBM, March 2006.
   Abstract: The Web Services Policy Framework (WS-Policy) provides a general purpose model and corresponding syntax to describe the policies of a Web Service. WS-Policy defines a base set of constructs that can be used and extended by other Web services specifications to describe a broad range of service requirements and capabilities.

2. The OASIS Group. Quality Model for Web Services. The Oasis Group, September 2005.
   Abstract: The purpose of this document is to provide a model for Web services quality management and quality factors in the process of developing and using Web services. We define the consistent and systematic conceptual model of Web services quality, which may be used by intimate associates, i.e. stakeholders, developers, service providers, and customers of Web services.

3. The Oasis Group. Summary of Quality Model for Web Services. The Oasis Group, 2005.

4. Heiko Ludwig, Alexander Keller, Asit Dan, Richard P. King, Richard Franck . Web Service Level Agreement (WSLA) Language Specification. IBM Corporation, 2003.
   Abstract: This document describes the specification language for service level agreements for Web Services, the Web Service Level Agreement (WSLA) language. WSLAs are agreements between a service provider and a customer and as such define the obligations of the parties involved. Primarily, this is the obligation of a service provider to perform a service according to agreed-upon guarantees for IT-level service parameters (such as availability, response time and throughput) for Web Services.
   An SLA also specifies the measures to be taken in case of deviation and failure to meet the asserted service guarantees, for example, a notification of the service customer. The assertions of the service provider are based on a detailed definition of service parameters including the algorithms - how basic metrics should be measured in systems and how they are aggregated into composite metrics and SLA parameters. In addition, a WSLA can express the operations of monitoring and managing the service. This may include third parties (such as Management Service Providers) that contribute to the measurement of metrics, supervision of guarantees or even the management of deviations of service guarantees. These multi-party constellations necessitate the definition of the interactions among the parties supervising the WSLA.
   However, a WSLA only covers the agreed common view of a service between the parties involved. To actually act as a participant in a WSLA, parties have various degrees of freedom to define an implementation policy for a service and its supervision. Typically, the obligations of a WSLA must be translated into system-level configuration information, which can be proprietary to each party involved.

5. Akhil Sahai, Anna Durante, Vijay Machiraju. Towards Automated SLA Management for Web Services. Num. HPL-2001-310, HP Laboratories, July 2002.
   Abstract: In order to automate SLA management it is essential to specify SLAs in precise and unambiguous manner as well as keep the specification flexible. While precision will help automate the process of monitoring and metric collection, flexibility will enable extending it to unforeseen service level agreement specifications.

6. Anbazhagan Mani, Arun Nagarajan. Understanding quality of service for Web services. IBM, 2002.
   Abstract: With the widespread proliferation of Web services, quality of service (QoS) will become a significant factor in distinguishing the success of service providers. QoS determines the service usability and utility, both of which influence the popularity of the service. In this article, we look at the various Web service QoS requirements, bottlenecks affecting performance of Web services, approaches of providing service quality, transactional services, and a simple method of measuring response time of your Web services using the service proxy.