An Empirical Evaluation of Client-side Server Selection Policies for Accessing Replicated Web Services

Replicating web services at geographically distributed servers can offer client applications with a number of benefits, including higher service availability and improved response time. However, selecting the “best ” server to invoke at the client side is not a trivial task, as this decision needs to account for (and is affected by) a number of factors, such as local connection capacity, external network conditions and servers workload. This paper presents the results of an experiment in which we implemented and empirically evaluated the performance of five server selection policies for accessing replicated web services. The experiment involved two client stations, with different connection capacities, continuously applying the five policies to invoke a real-world web service replicated over four servers in three continents. Our results show that, in addition to the individual performance of each server, service response time using the five policies is affected mainly by client differences in terms of connection capacity and workload distribution throughout the day

WS-mediator for improving dependability of service composition

Web Services and service-oriented architectures (SOAs) represent a new paradigm for building distributed computing applications. In recent years, they have started to play a critical role in numerous e-Science and e-Commerce applications. The advantages of Web Services, such as their loosely coupled architecture and standardized interoperability, make them a desirable platform, especially for developing large-scale applications such as those based on cross-organizational service composition. However, the Web Service technology is now facing many serious issues that need to be addressed, one of the most important ones being the dependability of their composition. Web Service composition relies on individual component services and computer networks, particularly the Internet. As the component services are autonomous, prior to use their dependability is unknown. In addition to that, computer networks are inherently unreliable media: from the user's perspective, network failures may undermine the dependability of Web Services. Consequently, failures of individual component services and of the network can undermine the dependability of the entire application relying on service composition. Our research is intended to contribute to achieving higher dependability of Web Service composition. We have developed a novel solution, called WS-Mediator system, implementing resilience-explicit computing and fault tolerance mechanisms to improve the dependability of Web Service composition. It consists of a number of subsystems, called Sub-Mediators, which are deployed at various geographical locations across the Internet to monitor Web Services and dynamically generate Web Service dependability metadata in order to make resilience-explicit decisions. In addition to applying the fault tolerance mechanisms that deal with various kinds of faults during the service composition, the resilience-explicit reconfiguration mechanism dynamically selects the most dependable Web Services to achieve higher service composition dependability fault tolerance. A specific instance of the WS-Mediator architecture has been developed in the Java Web Service technology. A series of experiments with real-world Web Services, in particular in the bioinformatics domain, have been carried out using the Java WS- Mediator. The results of the experiments have demonstrated the applicability of the WS-Mediator approach.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Security policy architecture for web services environment

An enhanced observer is model that observes behaviour of a service and then automatically reports any changes in the state of the service to evaluator model. The e-observer observes the state of a service to determine whether it conforms to and obeys its intended behaviour or policy rules. E-observer techniques address most problems, govern and provide a proven solution that is re-usable in a similar context. This leads to an organisation and formalisation policy which is the engine of the e-observer model. Policies are used to refer to specific security rules for particular systems. They are derived from the goals of management that describe the desired behaviour of distributed heterogeneous systems and networks. These policies should be defended by security which has become a coherent and crucial issue. Security aims to protect these policies whenever possible. It is the first line of protection for resources or assets against events such as loss of availability, unauthorised access or modification of data. The techniques devised to protect information from intruders are general purpose in nature and, therefore, cannot directly enforce security that has no universal definition, the high degree of assurance of security properties of systems used in security-critical areas, such as business, education and financial, is usually achieved by verification. In addition, security policies express the protection requirements of a system in a precise and unambiguous form. They describe the requirements and mechanisms for securing the resources and assets between the sharing parties of a business transaction. However, Service-Oriented Computing (SOC) is a new paradigm of computing that considers "services" as fundamental elements for developing applications/solutions. SOC has many advantages that support IT to improve and increase its capabilities. SOC allows flexibility to be integrated into application development. This allows services to be provided in a highly distributed manner by Web services. Many organisations and enterprises have undertaken developments using SOC. Web services (WSs) are examples of SOC. WSs have become more powerful and sophisticated in recent years and are being used successfully for inter-operable solutions across various networks. The main benefit of web services is that they use machine-to-machine interaction. This leads initially to explore the "Quality" aspect of the services. Quality of Service (QoS) describes many techniques that prioritise one type of traffic or programme that operates across a network connection. Hence, QoS has rules to determine which requests have priority and uses these rules in order to specify their priority to real-time communications. In addition, these rules can be sophisticated and expressed as policies that constrain the behaviour of these services. The rules (policies) should be addressed and enforced by the security mechanism. Moreover, in SOC and in particular web services, services are black boxes where behaviour may be completely determined by its interaction with other services under confederation system. Therefore, we propose the design and implementation of the “behaviour of services,” which is constrained by QoS policies. We formulate and implement novel techniques for web service policy-based QoS, which leads to the development of a framework for observing services. These services interact with each other by verifying them in a formal and systematic manner. This framework can be used to specify security policies in a succinct and unambiguous manner; thus, we developed a set of rules that can be applied inductively to verify the set of traces generated by the specification of our model’s policy. These rules could be also used for verifying the functionality of the system. In order to demonstrate the protection features of information system that is able to specify and concisely describe a set of traces generated, we subsequently consider the design and management of Ponder policy language to express QoS and its associated based on criteria, such as, security. An algorithm was composed for analysing the observations that are constrained by policies, and then a prototype system for demonstrating the observation architecture within the education sector. Finally, an enforcement system was used to successfully deploy the prototype’s infrastructure over Web services in order to define an optimisation model that would capture efficiency requirements. Therefore, our assumption is, tracing and observing the communication between services and then takes the decision based on their behaviour and history. Hence, the big issue here is how do we ensure that some given security requirements are satisfied and enforced? The scenario here is under confederation system and based on the following: System’s components are Web-services. These components are black boxes and designed/built by various vendors. Topology is highly changeable. Consequently, the main issues are: • The proposal, design and development of a prototype of observation system that manages security policy and its associated aspects by evaluating the outcome results via the evaluator model. • Taming the design complexity of the observation system by leaving considerable degrees of freedom for their structure and behaviour and by bestowing upon them certain characteristics, and to learn and adapt with respect to dynamically changing environments.Saudi Arabian Cultural Burea

Client-side Selection Of Replicated Web Services: An Empirical Assessment

Replicating web services over physically distributed servers can offer client applications a number of QoS benefits, including higher availability and reduced response time. However, selecting the "best" service replica to invoke at the client-side is not a trivial task, as this requires taking into account factors such as local and external network conditions, and the servers' current workload. This paper presents an empirical assessment of five representative client-side service selection policies for accessing replicated web services. The assessment measured the response time obtained with each of the five policies, at two different client configurations, when accessing a world-wide replicated service with four replicas located in three continents. The assessment's results were analyzed both quantitatively and qualitatively. In essence, the results show that, in addition to the QoS levels provided by the external network and the remote servers, characteristics of the local client environment can have a significant impact on the performance of some of the policies investigated. In this regard, the paper presents a set of guidelines to help application developers in identifying a server selection policy that best suits a particular service replication scenario. © 2007 Elsevier Inc. All rights reserved.81813461363Amini, L., Shaikh, A., Schulzrinne, H., Modeling redirection in geographically diverse server sets (2003) Proceedings of the 12th International World Wide Web Conference (WWW 2003), pp. 472-481. , ACM Press, Budapest, HungaryApache, 2006. AXIS Version 1.4. Available at http://ws.apache.org/axis/ (accessed 28.02.07)Cauldwell, P., Chawla, R., Chopra, V., (2001) Professional XML Web Services, , Wrox Press, Birminghan, USACosta, L.A.G., Pires, P.F., Mattoso, M., Automatic composition of web services with contingency plans (2004) Proceedings of the IEEE International Conference on Web Services (ICWS'04), , IEEE Computer Society Press, Washington, DC, USADamani, O., Chung, Y., Kintala, C., Wan, Y., ONE-IP: techniques for hosting a service on a cluster of machines (1997) Proceedings of the 6th International World Wide Web Conference (WWW'97), pp. 1019-1027. , Elsevier Science Publishers, Ltd., California, USADykes, S.G., Robbins, K.A., Jeffery, C.L., Empirical evaluation of client-side server selection algorithms (2000) Proceedings of the 19th Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2000), 3, pp. 1361-1370. , Tel Aviv, IsraelHanna, M.K., Natajaran, N., Levine, N.B., November 2001. Evaluation of a novel two-step server selection metric. In: Proceedings of the 9th IEEE International Conference on Network Protocols (ICNP'01). California, USA, p. 290Hu, J., Guo, C., Wang, H., Zou, P., Quality driven web services selection (2005) Proceedings of the IEEE International Conference on e-Business Engineering (ICEBE'04), pp. 681-688. , IEEE Computer Society PressKeidl, M., Kemper, A., A framework for context-aware adaptable web services (2004) Lecture Notes in Computer Science, 2992, pp. 826-829. , Proceedings of the 9th International Conference on Extending Database Technology (EDBT 2004), SpringerLiu, Y., Ngu, A.H.H., Zeng, L., QoS computation and policing in dynamic web service selection (2004) Proceedings of the 13th International World Wide Web Conference (WWW'04), pp. 66-73. , ACM Press, New York, NY, USAMakris, C., Panagis, Y., Sakkopoulos, E., Tsakalidis, A., Efficient and adaptive discovery techniques of web services handling large data sets (2006) Journal of Systems and Software, 79 (4), pp. 480-495Menascé, D., QoS issues in web services (2002) IEEE Internet Computing, 6 (2), pp. 72-75Mendonça, N.C., Silva, J.A.F., An empirical evaluation of client-side server selection policies for accessing replicated web services (2005) Proceedings of the 20th Annual ACM Symposium on Applied Computing (SAC 2005), Special Track on Web Technologies and Applications, pp. 1704-1708. , ACM Press, Santa Fé, New Mexico, USAMicrosoft, 2006. NET Framework Version 3.0. Available at http://www.microsoft.com/net/ (accessed 28.02.07)OASIS, 2002. Universal Description, Discovery e Integration (UDDI) Version 2.0. Available at http://www.oasis-open.org/committees/uddi-spec/doc/tcspecs.htm#uddiv2 (accessed 28.02.07)Ouzzani, M., Bouguettaya, A., Efficient access to web services (2004) IEEE Internet Computing, 8 (2), pp. 34-44Padovitz, A., Krishnaswamy, S., Loke, S.W., July 2003. Towards efficient and smart selection of web services. In: Proceedings of the Second International Joint Conference on Autonomous Agents and Multi-agent Systems (AAMAS 2003), Workshop on Web Services and Agent-based Engineering (WSABE). Melbourne, AustraliaPapazoglou, M.P., Georgakopoulos, D., Service-oriented computing: introduction (2003) Communications of the ACM, 46 (10), pp. 25-28Ran, S., A model for web services discovery with QoS (2003) ACM SIGecom Exchanges, 4 (1), pp. 1-10Rodriguez, P., Biersack, E.W., Dynamic parallel access to replicated content in the internet (2002) IEEE/ACM Transactions on Networking, 10 (4), pp. 455-465Salas, J., Pérez-Sorrosal, F., Patiño-Martínez, M., Jiménez-Peris, R., WS-Replication: a framework for highly available web services (2006) Proceedings of the Fifteenth International World Wide Web Conference (WWW 2006), pp. 357-366. , ACM Press, Edinburgh, ScotlandSayal, M., Breitbart, Y., Scheuermann, P., Vingralek, R., Selection algorithms for replicated web servers (1998) ACM SIGMETRICS Performance Evaluation Review, 26 (3), pp. 44-50Serhani, M.A., Dssouli, R., Hafid, A., Sahraoui, H., A QoS broker based architecture for efficient web services selection (2005) Proceedings of the IEEE International Conference on Web Services (ICWS'05), pp. 113-120. , IEEE Computer Society PressSUN, 2006. Java Web Services Developer Pack (JWSDP) Version 2.0. Available at http://java.sun.com/webservices/downloads/webservicespack.html (accessed 28.02.07)Tian, M., Gramm, A., Ritter, H., Schiller, J., Efficient selection and monitoring of QoS-aware web services with the WS-QoS Framework (2004) Proceedings of the IEEE/WIC/ACM International Conference on Web Intelligence (WI'04), pp. 152-158. , IEEE Computer Society PressW3C, 2001. Web Services Definition Language (WSDL) Version 1.1, W3C Note 15. Available at http://www.w3.org/TR/wsdl (accessed 28.02.07)W3C, 2003. Simple Object Access Protocol (SOAP) Version 1.2, W3C Note 08. Available at http://www.w3.org/TR/SOAP/ (accessed 28.02.07)Yoshikawa, C., Chun, B., Eastham, P., Vahdat, A., Anderson, T., Culler, D., 1997. Using Smart Clients to Build Scalable Services. In: Proceedings of the USENIX Annual Technical Conference. Anaheim, California, USAYu, T., Lin, K.-J., A broker-based framework for QoS-aware web service composition (2005) Proceedings of the IEEE International Conference on E-Technology, E-Commerce and E-Service (EEE'05), pp. 22-29. , IEEE Computer Society PressYu, T., Lin, K.-J., Service selection algorithms for web services with end-to-end QoS constraints (2005) Journal of Information Systems and E-Business Management, 3 (2), pp. 103-126Zhou, C., Chia, L.-T., Lee, B.-S., QoS-aware and federated enhancement for UDDI (2004) International Journal of Web Services Research, 1 (2), pp. 58-85Zhuge, H., Liu, J., Flexible retrieval of web services (2004) Journal of Systems and Software, 70 (1-2), pp. 107-11