Publications in Quality of Service

Articles in Refereed Journals:

1. 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.

2. Stefano Bistarelli, Ugo Montanari, Francesca Rossi, Francesco Santini. Unicast and Multicast Qos Routing with Soft Constraint Logic Programming. CoRR, Vol. abs/0704.1783, 2007.
   Abstract: We present a formal model to represent and solve the unicast/multicast routing problem in networks with Quality of Service (QoS) requirements. To attain this, first we translate the network adapting it to a weighted graph (unicast) or and-or graph (multicast), where the weight on a connector corresponds to the multidimensional cost of sending a packet on the related network link: each component of the weights vector represents a different QoS metric value (e.g. bandwidth, cost, delay, packet loss). The second step consists in writing this graph as a program in Soft Constraint Logic Programming (SCLP): the engine of this framework is then able to find the best paths/trees by optimizing their costs and solving the constraints imposed on them (e.g. delay < 40msec), thus finding a solution to QoS routing problems. Moreover, c-semiring structures are a convenient tool to model QoS metrics. At last, we provide an implementation of the framework over scale-free networks and we suggest how the performance can be improved.

3. Giorgia Lodi, Fabio Panzieri, Davide Rossi, Elisa Turrini. SLA-Driven Clustering of QoS-Aware Application Servers. IEEE Trans. Software Eng., Vol. 33, Num. 3, pages 186-197, 2007.
   Abstract: In this paper, we discuss the design, implementation, and experimental evaluation of a middleware architecture for enabling service level agreement (SLA)-driven clustering of QoS-aware application servers. Our middleware architecture supports application server technologies with dynamic resource management: application servers can dynamically change the amount of clustered resources assigned to hosted applications on-demand so as to meet application-level quality of service (QoS) requirements. These requirements can include timeliness, availability, and high throughput and are specified in SLAs. A prototype of our architecture has been implemented using the open-source J2EE application server JBoss. The evaluation of this prototype shows that our approach makes possible JBoss' resource usage optimization and allows JBoss to effectively meet the QoS requirements of the applications it hosts, i.e., to honor the SLAs of those applications.

4. Tao Yu, Kwei-Jay Lin. Service selection algorithms for Web services with end-to-end QoS constraints. Inf. Syst. E-Business Management, Vol. 3, Num. 2, pages 103-126, 2005.
   Abstract: Web services are new forms of Internet software that can be universally deployed and invoked using standard protocols. Services from different providers can be integrated into a composite service regardless of their locations, platforms, and/or execution speeds to implement complex business processes and transactions. In this paper, we study the end-to-end QoS issues of composite services by utilizing a QoS broker that is responsible for selecting and coordinating the individual service component. We design the service selection algorithms used by QoS brokers to construct the optimal composite service. The objective of the algorithms is to maximize the user-defined utility function value while meeting the end-to-end delay constraint. We propose two solution approaches to the service selection problem: the combinatorial approach, by modeling the problem as the Multiple Choice Knapsack Problem (MCKP), and the graph approach, by modeling the problem as the constrained shortest path problem in the graph theory. We study efficient solutions for each approach.

5. Liangzhao Zeng, Benatallah, B., Ngu, A.H.H., Dumas, M., Kalagnanam, J., Chang, H.. QoS-aware middleware for Web services composition. Software Engineering, IEEE Transactions on, Vol. 30, Num. 5, pages 311-327, May 2004.
   Abstract: The paradigmatic shift from a Web of manual interactions to a Web of programmatic interactions driven by Web services is creating unprecedented opportunities for the formation of online business-to-business (B2B) collaborations. In particular, the creation of value-added services by composition of existing ones is gaining a significant momentum. Since many available Web services provide overlapping or identical functionality, albeit with different quality of service (QoS), a choice needs to be made to determine which services are to participate in a given composite service. This paper presents a middleware platform which addresses the issue of selecting Web services for the purpose of their composition in a way that maximizes user satisfaction expressed as utility functions over QoS attributes, while satisfying the constraints set by the user and by the structure of the composite service. Two selection approaches are described and compared: one based on local (task-level) selection of services and the other based on global allocation of tasks to services using integer programming.

6. Xavier Franch, Juan Pablo Carvallo. Using Quality Models in Software Package Selection. IEEE Software, Vol. 20, Num. 1, pages 34-41, 2003.
   Abstract: The growing importance of commercial off-the-shelf software packages requires adapting some software engineering practices, such as requirements elicitation and testing, to this emergent framework. Also, some specific new activities arise, among which selection of software packages plays a prominent role. All the methodologies that have been proposed recently for choosing software packages compare user requirements with the packages' capabilities. There are different types of requirements, such as managerial, political, and, of course, quality requirements. Quality requirements are often difficult to check. This is partly due to their nature, but there is another reason that can be mitigated, namely the lack of structured and widespread descriptions of package domains (that is, categories of software packages such as ERP systems, graphical or data structure libraries, and so on). This absence hampers the accurate description of software packages and the precise statement of quality requirements, and consequently overall package selection and confidence in the result of the process. Our methodology for building structured quality models helps solve this drawback.

7. Shuping Ran. A model for web services discovery with QoS. SIGecom Exch., Vol. 4, Num. 1, pages 1-10, ACM, 2003.
   Abstract: Web services technology has generated a lot interest, but its adoption rate has been slow. This paper discusses issues related to this slow take up and argues that quality of services is one of the contributing factors. The paper proposes a new Web services discovery model in which the functional and non-functional requirements (i.e. quality of services) are taken into account for the service discovery. The proposed model should give Web services consumers some confidence about the quality of service of the discovered Web services.

8. Menasce, D.A.. QoS Issues in Web Services. Internet Computing, IEEE, Vol. 6, Num. 6, pages 72-75, November/December 2002.
   Abstract: Quality of service (QoS) is a combination of several qualities or properties of a service, such as: availability is the percentage of time that a service is operating; security properties include the existence and type of authentication mechanisms the service offers, confidentiality and data integrity of messages exchanged, nonrepudiation of requests or messages, and resilience to denial-of-service attacks; response time is the time a service takes to respond to various types of requests; Response time is a function of load intensity, which can be measured in terms of arrival rates (such as requests per second) or number of concurrent requests. QoS takes into account not only the average response time, but also the percentile of the response time; and throughput is the rate at which a service can process requests. QoS measures can include the maximum throughput or a function that describes how throughput varies with load intensity. The QoS measure is observed by Web services users. These users are not human beings but programs that send requests for services to Web service providers. QoS issues in Web services have to be evaluated from the perspective of the providers of Web services and from the perspective of the users of these services.

Articles in Refereed Conferences:

1. Kyriakos Kritikos, Dimitris Plexousakis. Evaluation of QoS-Based Web Service Matchmaking Algorithms. International Conference on Services Computing, 2008.
   Abstract: Web Service (WS) discovery is a prerequisite for achieving WS composition and orchestration. Although a lot of esearch has been conducted on the functional discovery of WSs, the proposed techniques fall short when faced with the foreseen increase in the number of (potentially functionally- equivalent) WSs. The above situation can be resolved with the addition of non-functional (Quality of Service (QoS)) discovery mechanisms to WS discovery engines. QoS-based WS matchmaking algorithms have been devised for this reason. However, they are either slow - as they are based on ontology reasoners - or produce inaccurate results. Inaccuracy is caused both by the syntactic matching of QoS concepts and by wrong matchmaking metrics. In this paper, we present two Constraint Programming (CP) QoS-based WS discovery algorithms for unary constrained WS specifications that produce accurate results with good performance. We also evaluate these algorithms on matchmaking time, precision and recall in different settings in order to demonstrate their efficiency and accuracy.

2. Kyriakos Kritikos, Dimitris Plexousakis. OWL-Q for Semantic QoS-based Web Service Description and Discovery. First International Joint Workshop on Service Matchmaking and Resource Retrieval in the Semantic Web, November 2007.
   Abstract: Semantic Web Services are emerging for their promise to produce a more accurate and precise Web Service discovery process. However, most of research approaches focus only on the functional part of semantic Web Service description. The above fact along with the proliferation of Web Services is highly probable to lead to a situation where Web Service registries will return many functionally-equivalent Web Service advertisements for each user request. This problem can be solved with the semantic description of QoS for Web Services. QoS is a set of non-functional properties encompassing performance and network- related characteristics of resources. So it can be used for distinguishing between functionally-equivalent Web Services. Current research approaches for QoS-based Web Service description are either syntactic or poor or non-extensible. To solve this problem, we have developed a rich and extensible ontological specification called OWL-Q for semantic QoS-based Web Service description. We analyze all OWL-Q parts and reason that rules should be added in order to support property inferencing and constraint enforcement. Finally, we line out our under-development semantic framework for QoS-based Web Service description and discovery.

3. Cinzia Cappiello, Marco Comuzzi, Pierluigi Pleban. On Automated Generation of Web Service Level Agreements . Advanced Information Systems Engineering, Vol. 4495, Springer Verlag, June 2007.
   Abstract: Before a service invocation takes place, an agreement between the service provider and the service user might be required. Such an agreement is the result of a negotiation process between the two parties and defines how the service invocation has to occur. Considering the Service Oriented Computing paradigm, the relationship among providers and users is extremely loose. Traditional agreements are likely to concern long term relationships and to be manually performed. In this paper, we propose a model to generate service level agreement on-the-fly. Just before the invocation commences, the quality of the service is negotiated in order to generate a service level agreement tied to that specific invocation. Such an approach relies on a quality model that supports both users requirements and providers capabilities definition.

4. Jonatha Anselmi, Danilo Ardagna, Paolo Cremonesi. A QoS-based selection approach of autonomic grid services. SOCP '07: Proceedings of the 2007 workshop on Service-oriented computing performance: aspects, issues, and approaches, pages 1-8, ACM, 2007.
   Abstract: The Web service composition (WSC) is the process of building an instance of an abstract workflow by combining appropriate Web services that satisfies given QoS requirements. In general, QoS requirements consists of a number of constraints. The selection process requires global optimization and can be formalized as a mixed integer linear programming problem which cannot be solved in polynomial time. However, since the number of submitted workflows is large and the QoS is highly dynamic, the fast selection of composite Web Services is particularly important. In this paper, we present a QoS broker-based framework for Web services execution in autonomic grid environments. The main goal of the framework is to support the broker in selecting Web services based on the required QoS. To achieve this goal, we propose a novel approach: since successive composed Web services requests can have the same task to Web service assignment, we address the Multiple Instance WSC (MI-WSC) problem optimizing simultaneously the set of requests which will be submitted to the system in the successive time interval instead of independently computing a solution for each incoming request. Experimental results show that the proposed algorithm has better performance with respect to existing techniques. Moreover, the qualities of the selected composite Web services are not significantly different from the optimal ones.

5. Ester Giallonardo, Eugenio Zimeo. More Semantics in QoS Matching. SOCA, pages 163-171, 2007.
   Abstract: The evolution of the Web towards a global computing environment is promoting new research efforts aimed at the formal characterization of Web Services QoS. Reasoning on QoS is a key to improve matching process during the discovery of desired services and a step towards the transformation of applications in collections of loosely coupled services virtually connected by semantic similarities. The paper presents the on QoS ontology, an openly available OWL ontology for QoS, and evaluates it in a QoS-aware matching environment. The ontology can be used to express functions of QoS metrics useful to improve the recall tied to the matching of a template request with target Web Services. To this end, the ontology introduces the concept of derivation in the matching process. This gives the possibility of matching a QoS template with published Web Services by deriving different QoS parameters when a one-to-one matching fails. The proposed matching algorithm utilizes a reasoner that exploits the ontology to avoid apparent mismatches. An experimental evaluation shows that exploiting QoS knowledge significantly improves matching recall without deteriorating precision.

6. Kyriakos Kritikos, Dimitris Plexousakis. Requirements for QoS-based Web Service Description and Discovery. COMPSAC (2), pages 467-472, 2007.
   Abstract: The goal of Service Oriented Architectures is to enable the creation of business applications through the automatic discovery and composition of independently developed and deployed (Web) services. Automatic discovery of Web Services (WSs) can be achieved by incorporating semantics into a richer WS description model (WSDM) and the use of Semantic Web (SW) technologies in the WS matchmaking and selection models. A sufficiently rich WSDM should encompass not only functional but also non-functional aspects like Quality of Service (QoS). QoS is a set of performance attributes that has a substantial impact on WS requesters' expectations. Thus, it can be used as a discriminating factor of functionally-equivalent WSs. The focus of this paper is twofold: to analyze the requirements of a semantically rich QoS-based WSDM and to provide SW and constrainedbased mechanisms for enriching syntactic QoS-based WS Discovery (WSDi) algorithms. In addition, a roadmap of extending WS standard techniques for realizing semantic, functional and QoS-based WSDi is presented.

7. Kyriakos Kritikos, Dimitris Plexousakis. Semantic QoS-based Web Service Discovery Algorithms. Fifth European Conference on Web Services, pages 181-190, IEEE Computer Society, 2007.
   Abstract: The success of the Web Service (WS) paradigm has led to a proliferation of available WSs, which are advertised in WS registries. While sophisticated semantic WS discovery algorithms are operating on these registries to return matchmaking results with high precision and recall, many functionally-equivalent WSs are returned. The solution to the above problem comes in terms of semantic QoS-based description and discovery of WSs. We have already presented a rich and extensible ontology language for QoS-based WS description called OWL-Q. We have also proposed a semantic QoS metric matching algorithm. Based on this algorithm, we have extended a CSP-based approach for QoS-based WS discovery. In this paper, we firstly analyze the evolution of OWL-Q and its extension with SWRL rules, we propose a modification to the metric matching algorithm and we show the way the metric alignment process takes place. Then we propose two novel semantic QoS-based WS Discovery algorithms that return matches even for over-constrained QoS-based WS requests. The first one deals with unary constraints while the second one is more generic. Finally, implementation aspects of our QoS-based WS discovery system are discussed.

8. Qing Zhu, Shan Wang, Guorong Li, Guangqiang Liu, Xiaoyong Du. QoS-Based Services Selecting and Optimizing Algorithms on Grid. APWeb/WAIM Workshops, pages 156-167, 2007.
   Abstract: QoS-Based Services Selecting and Optimizing Composition between the peers play an increasingly important role to ensure interoperability on Grid environment. However, the prohibitive cost of selecting, matching, mapping and composing algorithm has now become a key bottleneck hindering the deployment of a wide variety of Grid services. In this paper, we present QoS-Based Services Selecting and Optimizing Composition on Grid. First, it checks requesters' semantic in order to form candidate service graph. Second, it designs service selecting and mapping algorithms for optimizing the model. Third, it creates an executed plan of optimum composition on Grid. We conducted experiments to simulate and evaluate our approach.

9. Dmytro Rud, Andreas Schmietendorf, Reiner Dumke. Performance Modeling of WS-BPEL-Based Web Service Compositions. Services Computing Workshops, pages 140-147, September 2006.
   Abstract: This paper addresses quality of service aspects of Web service orchestrations created using WS-BPEL from the standpoint of a Web service integrator. A mathematical model based on operations research techniques and formal semantics of WS-BPEL is proposed to estimate and forecast the influence of the execution of orchestrated processes on utilization and throughput of individual involved nodes and of the whole system. This model is applied to the optimization of service levels agreement process between the involved parties

10. Yan-ping Chen, Zeng-zhi Li, Qin-xue Jin, Chuang Wang. Study on QoS Driven Web Services Composition. Frontiers of WWW Research and Development - APWeb 2006, Lecture Notes on Computer Science, Vol. 3841, pages 702-707, Springer Verlag, 2006.
    Abstract: Providing composed Web Services based on the QoS requirements of clients is still an urgent problem to be solved. In this paper, we try to solve this problem. Firstly, we enhanced the current WSDL to describe the QoS of services, and then gave a way to choose the proper pre-exist services based on their QoS.

11. Kyriakos Kritikos, Dimitris Plexousakis. Semantic QoS Metric Matching. ECOWS, pages 265-274, 2006.
    Abstract: As the Web Service paradigm gains popularity for its promise to transform the way business is conducted, the number of deployed Web Services grows with a fast rate. While sophisticated semantic discovery mechanisms have been invented to overcome the UDDI's syntactic discovery solution in order to provide more recallable and precise results, the amount of functionally equivalent Web Services returned is still large. The solution to this problem is the description of the QoS non-functional aspect of Web Services. QoS encompasses the performance of Web Services and can be used as a discriminator factor for refining Web Service advertisement result lists. However, most scientific efforts presented so far are purely syntactic and are not capturing all aspects of QoS-based Web Service description leading to imprecise syntactic discovery mechanisms. This paper presents a novel, rich and extensible ontology-based approach for describing QoS of Web Services that complements OWL-S. It is shown that, by using this approach and by introducing the concept of semantic QoS metric matching, QoS-based syntactic matchmaking and selection algorithms are transformed to semantic ones leading to better results.

12. Gerardo Canfora, Massimiliano Di Penta, Raffaele Esposito, Maria Luisa Villani. An approach for QoS-aware service composition based on genetic algorithms. GECCO '05: Proceedings of the 2005 conference on Genetic and evolutionary computation, pages 1069-1075, ACM, 2005.
    Abstract: Web services are rapidly changing the landscape of software engineering. One of the most interesting challenges introduced by web services is represented by Quality Of Service (QoS)-aware composition and late-binding. This allows to bind, at run-time, a service-oriented system with a set of services that, among those providing the required features, meet some non-functional constraints, and optimize criteria such as the overall cost or response time. In other words, QoS-aware composition can be modeled as an optimization problem.We propose to adopt Genetic Algorithms to this aim. Genetic Algorithms, while being slower than integer programming, represent a more scalable choice, and are more suitable to handle generic QoS attributes. The paper describes our approach and its applicability, advantages and weaknesses, discussing results of some numerical simulations.

13. Gerardo Canfora, Massimiliano Di Penta, Raffaele Esposito, Maria Luisa Villani. QoS-Aware Replanning of Composite Web Services. ICWS '05: Proceedings of the IEEE International Conference on Web Services, pages 121-129, IEEE Computer Society, 2005.
    Abstract: Run-time service discovery and late-binding constitute some ofthe most challenging issues of service-oriented software engineering.For late-binding to be effective in the case of composite services,a QoS-aware composition mechanism is needed. This meansdetermining the set of services that, once composed, not only willperform the required functionality, but also will best contribute toachieve the level of QoS promised in Service Level Agreements (SLAs). However, QoS-aware composition relies on estimated QoS values and workflow execution paths previously obtained using a monitoring mechanism. At run-time, the actual QoS valuesmay deviate from the estimations, or the execution path may not bethe one foreseen. These changes could increase the risk of breakingSLAs and obtaining a poor QoS. Such a risk could be avoided byreplanning the service bindings of the workflow slice still to be executed. This paper proposes an approach to trigger and perform compositeservice replanning during execution. An evaluation has been performedsimulating execution and replanning on a set of composite serviceworkflows.

14. Casey K. Fung, Patrick C. K. Hung, Guijun Wang, Richard C. Linger, Gwendolyn H. Walton. A Study of Service Composition with QoS Management. ICWS, pages 717-724, 2005.
    Abstract: Quality of service (QoS) management in compositions of services requires careful consideration of QoS characteristics of the services and effective QoS management in their execution. A Web service is a software system that supports interoperable application-to-application interaction over the Internet. Web services are based on a set of XML standards such as simple object access protocol (SOAP). The interactions of SOAP messages between Web services form the theoretical model of SOAP message exchange patterns (MEP). Web Services Business Process Execution Language (WSBPEL) defines an interoperable integration model that facilitates automated process integration in intra- and inter-corporate environments. A service-level agreement (SLA) is a formal contract between a Web services requestor and provider guaranteeing quantifiable issues at defined levels only through mutual concessions. Based on a prior research work on message detail record (MDR), this paper further proposes a SOAP message tracking model for supporting QoS end-to-end management in the context of WSBPEL and SLA. This paper motivates the study of QoS management in a Web service composition framework with the evolution of a distributed toolkit in an industrial setting.

15. Michael C. Jaeger, Gero Mühl, Sebastian Golze. QoS-Aware Composition of Web Services: A Look at Selection Algorithms. ICWS, pages 807-808, 2005.
    Abstract: When a composition of Web services is designed, available services are put together to form a defined flow of executions. In a discovery process, a trader proposes available Web services as potential candidates. In a succeeding selection, for each task a trader chooses one candidate to form the optimal composition due to selection criteria. This paper discusses how the selection can consider different quality-of-service (QoS) categories to determine the most suitable candidates for the composition. If more than one category is used for optimisation, a multi-dimensional optimisation problem arises. This mentions similarities to similar combinatorial problems. Then, possible solutions are proposed and their performance is evaluated.

16. Vikas Deora, Jianhua Shao, Gareth Shercliff, Patrick J. Stockreisser, W. A. Gray, N. J. Fiddian. Incorporating QoS Specifications in Service Discovery. WISE Workshops, pages 252-263, 2004.
    Abstract: In this paper, we extend the current approaches to service discovery in a service oriented computing environment, such as Web Services and Grid, by allowing service providers and consumers to express their promises and requirements for quality of service (QoS). More specifically, we allow service providers to advertise their services in an extended DAML-S that supports quality specifications, and we allow service consumers to request services by stating required quality levels. We propose a model here for incorporating QoS specifications and requirements in service discovery, and describe how matchmaking between advertised and requested services based on functional as well as quality requirements is supported in our model.

17. Michael C. Jaeger, Gregor Rojec-Goldmann, Gero Mühl. QoS Aggregation for Web Service Composition using Workflow Patterns. EDOC, pages 149-159, 2004.
    Abstract: Contributions in the field of Web services have identified that (a) finding matches between semantic descriptions of advertised and requested services and (b) nonfunctional characteristics - the quality of service (QoS) - are the most crucial criteria for composition of Web services. A mechanism is introduced that determines the QoS of a Web service composition by aggregating the QoS dimensions of the individual services. This allows to verify whether a set of services selected for composition satisfies the QoS requirements for the whole composition. The aggregation performed builds upon abstract composition patterns, which represent basic structural elements of a composition, like sequence, loop, or parallel execution. This work focusses on workflow management environments. We define composition patterns that are derived from Van der Aalst's et al. comprehensive collection of workflow patterns. The resulting aggregation schema supports the same structural elements as found in workflows. Furthermore, the aggregation of several QoS dimensions is discussed.

18. James Skene, D. Davide Lamanna, Wolfgang Emmerich. Precise Service Level Agreements. ICSE, pages 179-188, 2004.
    Abstract: SLAng is an XML language for defining service level agreements, the part of a contract between the client and provider of an Internet service that describes the quality attributes that the service is required to possess. We define the semantics of SLAng precisely by modelling the syntax of the language in UML, then relating the language model to a model that describes the structure and behaviour of services. The presence of SLAng elements imposes behavioural constraints on service elements, and the precise definition of these constraints using OCL constitutes the semantic description of the language. We use the semantics to define a notion of SLA compatibility, and an extension to UML that enables the modelling of service situations as a precursor to analysis, implementation and provisioning activities.

19. Tao Yu, Kwei-Jay Lin. Service Selection Algorithms for Web Services with End-to-End QoS Constraints. CEC, pages 129-136, 2004.
    Abstract: Web services are new forms of Internet software that can be universally deployed and invoked using standard protocol. Services from different providers can be integrated to provide composite services. In this paper, we study the end-to-end QoS issues of composite service by utilizing a QoS broker that is responsible for coordinating the individual service component to meet the quality constraint. We design the service selection algorithms used by QoS brokers to meet end-to-end QoS constraints. The objective of the algorithms is to maximize the user-defined utility while meeting the end-to-end delay constraint. We model the problem as the Multiple Choice Knapsack Problem (MCKP) and provide efficient solutions. The algorithms are tested for their performance.

20. Vikas Deora, Jianhua Shao, W. A. Gray, N. J. Fiddian. A Quality of Service Management Framework Based on User Expectations. ICSOC, pages 104-114, 2003.
    Abstract: The ability to gauge the quality of a service is critical if we are to achieve the service oriented computing paradigm. Many techniques have been proposed and most of them attempt to calculate the quality of a service by collecting quality ratings from the users of the service, then combining them in one way or another. We argue that collecting quality ratings alone from the users is not sufficient for deriving a reliable or accurate quality measure for a service. This is because different users often have different expectations on the quality of a service and their ratings tend to be closely related to their expectations, i.e. how their expectations are met. In this paper, we propose a quality of service management framework based on user expectations. That is, we collect expectations as well as ratings from the users of a service, then calculate the quality of the service only at the time a request for the service is made and only using the ratings that have similar expectations. We give examples to show that our approach can result in a more accurate and meaningful measure for quality of service.

21. Octavio Martín-Díaz, Antonio Ruiz Cortés, Amador Durán, David Benavides, Miguel Toro. Automating the Procurement of Web Services. ICSOC, pages 91-103, 2003.
    Abstract: As government agencies and business become more dependent on web services, software solutions to automate their procurement gain importance. Current approaches for automating the procurement of web services suffer from an important drawback: neither uncertainty measures nor non-linear, and complex relations among parameters can be used by providers to specify quality-of-service in offers. In this paper, we look deeply into the roots of this drawback and present a proposal which overcomes it. The key point to achieve this improvement has been using the constraint programming as a formal basis, since it endows the model with a very powerful expressiveness. A XML-based implementation is presented along with some experimental results and comparisons with other approaches.

22. 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.

23. Vladimir Tosic, Kruti Patel, Bernard Pagurek. WSOL - Web Service Offerings Language. CAiSE '02/ WES '02: Revised Papers from the International Workshop on Web Services, E-Business, and the Semantic Web, pages 57-67, Springer-Verlag, 2002.
    Abstract: 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.

Books and Monographs:

1. J. Cardoso. Quality of Service and Semantic Composition of Workflows. Ph.D. Thesis, University of Georgia, 2002.
   Abstract: Workflow management systems (WfMSs) have been used to support a variety of business processes. As organizations adopt new working models, such as e-commerce, new challenges arise for workflow systems. These challenges include support for the adequate management of quality of service (QoS) and the development of new solutions to facilitate the composition of workflow applications involving Web services. The good management of QoS directly impacts the success of organizations participating in e- commerce activities by better fulfilling customer expectations and achieving customer satisfaction. To enable adequate QoS management, research is required to develop mechanisms that specify, compute, monitor, and control the QoS of the products or services to be delivered. The composition of workflows to model e-service applications differs from the design of traditional workflows due to the number of Web services available during the composition process and to their heterogeneity. Two main problems need to be solved: how to efficiently discover Web services and how to facilitate their interoperability. To enhance WfMSs with QoS management, we have developed a QoS model that allows for the description of nonfunctional aspects of workflow components, from a quality of service perspective. To automatically compute the overall QoS of a workflow, we have developed a mathematical model and implemented an algorithm (SWR algorithm). Our QoS model and mathematical model have been validated with the deployment and execution of a set of production workflows in the area of genetics. The analysis of the collected data proves that our models provide a suitable framework for estimating, predicting, and analyzing the QoS of production workflows. To support, facilitate, and assist the composition of workflows involving Web services, we present a solution based on ontologies. We have developed an algorithm that workflow systems and discovery mechanisms can use to find Web services with desired interfaces and operational metrics, and to assist designers in resolving heterogeneity issues among Web services. Our approach provides an important solution to enhance Web service discovery and interoperability.

Publications in Refereed Workshops:

1. M. Tian, A. Gramm, T. Naumowicz, H. Ritter, J. Schiller. A Concept for QoS Integration in Web Services. Web Information Systems Engineering Workshops, pages 149-155, December 2003.
   Abstract: With the growing popularity of Web services, a general QoS support for Web services plays an important role for the success of this emerging technology. Unfortunately, current Web service environments do not offer comprehensive QoS support. In this paper, we present an approach that does not only enable the QoS integration in Web services, but also the selection of appropriate services based on QoS requirements regarding server and network performance. Furthermore, we present how application requirements regarding communication QoS are mapped onto the underlying QoS aware network at runtime, as well as how users can obtain real-time information about server performance in order to monitor the accomplishment of assured services, giving the user an instant QoS feedback.

2. Sabata, B., Chatterjee, S., Davis, M., Sydir, J.J., Lawrence, T.F.. Taxonomy for QoS specifications. pages 100-107, 1997.
   Abstract: It is becoming increasingly commonplace for multiple applications with different quality of service (QoS) requirements to share the resources of a distributed system. Within this environment, the resource management algorithms must take into account the QoS desired by applications and the ability of the system resources to provide it. We present a taxonomy for specifying QoS for the different components of a distributed system, from the applications down to the resources. We specify QoS as a combination of metrics and policies. QoS metrics are used to specify performance parameters, security requirements and the relative importance of the work in the system. We define three types of QoS performance parameters: timeliness, precision, and accuracy. QoS policies capture application-specific policies that govern how an application is treated by the resource manager. Examples of such policies are management policies and the levels of service. We explore each of these components of the QoS taxonomy in detail

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. Alain Andrieux, Karl Czajkowski, Asit Dan, Kate Keahey, Heiko Ludwig, Toshiyuki Nakata, Jim Pruyne, John Rofrano, Steve Tuecke, Ming Xu. Web Services Agreement Specification (WS-Agreement). Grid Resource Allocation Agreement Protocol, September 2005.
   Abstract: This document describes Web Services Agreement Specification (WS-Agreement), a Web Services protocol for establishing agreement between two parties, such as between a service provider and consumer, using an extensible XML language for specifying the nature of the agreement, and agreement templates to facilitate discovery of compatible agreement parties. The specification consists of three parts which may be used in a composable manner: a schema for specifying an agreement, a schema for specifying an agreement template, and a set of port types and operations for managing agreement life-cycle, including creation, expiration, and monitoring of agreement states.

3. 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.

4. The OMG Group. UML$^\mathrm{TM}$ Profile for Modeling Quality of Service and Fault Tolerance Characteristics and Mechanisms. Num. ptc/2005-05-02, The OMG Group, May 2005.

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

6. 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.

7. 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.

8. 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.

9. Svend Frolund, Jari Koistinen. QML: A Language for Quality of Service Specification. Num. HPL-98-10, 63 pages, HP Laboratories, 1998.
   Abstract: To be competitive, future software system must provide not only the correct functionality, but also an adequate level of quality of service (QoS). By QoS, we refer to non-functional properties, such as reliability, performance, timing, and security. To provide an adequate level of QoS, software systems need to include capabilities such as QoS negotiation, monitoring, and adaptation. These capabilities all require the expected and the provided QoS levels to be explicitly specified. QoS can be specified statically at the time of implementation, design, or dynamically at deployment or runtime. To facilitate QoS specification, we present a general Quality of service Modeling Language (QML) for defining multi-category QoS specifications for components in distributed object systems. QML is designed to support QoS in general, encompassing QoS categories such as reliability, performance, security, and timing. QoS specification in QML facilitate the static decomposition of a software system into components with precisely specified QoS boundaries. They also facilitate dynamic QoS functions, such as negotiations, monitoring, and adaptation. QML is designed for a good fit with object-oriented distributed architectures and concepts such as interfaces and inheritance. It also allows specification at a fine-grained level for operations, operation arguments, and attributes. QML enables user- defined QoS categories, and allows specifications within those categories to be associated with component interface definitions. In addition, checks can be made dynamically to determine whether one QML specification satisfies another. This mechanism allows us to dynamically match QoS requirements and offers