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Web Service discovery based on Quality of Service Yannis Makripoulias2, Christos Makris1,2, Yiannis Panagis1,2, Evangelos Sakkopoulos1,2, Poulia Adamopoulou1,2 and Athanasios Tsakalidis1,2 E-mail: {makripou, makri, panagis, adamopop}@ceid.upatras.gr, {sakkopul,tsak}@cti.gr 1
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Research Academic Computer Technology Institute Internet and Multimedia Technologies Research Unit N. Kazantzaki Str. 26504 Patras, Greece
the results using quality criteria, such as price, network distance and execution time etc. This work is organized as follows. In section 2 related work and the contribution of this proposal is outlined. Section 3 includes a short overview of our mechanism’s design. Section 4 presents details and discusses the architectural approach. Next, section 5 discusses implementation issues. In section 6 experimental evaluation of the proposed solution is presented. Finally section 7 discusses conclusions and future research steps.
Abstract Late developments in Web Service discovery approaches mainly focus on the incorporation of the QoS concept in the selection process. In this paper, we present a generalized design and implementation of a QoS enabled Web Service discovery mechanism. We describe a mechanism extending the propositions of [1] in a generalized environment that consists of dynamic groups/ categories of different Web Services. A UDDI search wrapper is introduced to facilitate the traditional WS discovery by taking into account QoS characteristics in transparent way. Our aim is the combination of the classic Web Service discovery, at design or execution time, with the benefit of QoS characteristics without affecting the existing UDDI search facilities. To evaluate the functionality, feasibility and effectiveness of the mechanism proposed, a number of experimental applications have been developed. All applications have been available for evaluation online in laboratory.
2. Related Work, Motivation And Contribution Web Service Discovery mechanisms have been reviewed extensively in the work of [8]. In general, these mechanisms do not usually take into account QoS concerns such as the response time. However, in a realworld invocation environment, aspects such as response time are paramount [5]. Ran et al [6], presented some desirable characteristics that define Quality of Web Service (QoWS). In this work we have chosen to extend the open model for calculating the QoS for WS selection discussed in [1]. Our approach supports QoS enhancements for all Web Services that are registered in a UDDI catalogue and does not limit itself to a local broker-dependant registry. In fact multiple UDDI registers can be queried transparently. Additionally, QoS parameters are separately stored in a dedicated storage system to facilitate UDDI catalogues which do not support QoS information storage. In [1], the requester selects the quality criteria to give the greatest emphasis in. In the following, a list of the most appropriate Web Services is returned for selection from a predefined list according to these criteria. Thus, the value of the QoS remains static as long as the predefined list doesn’t change. In fact, QoS calculation is based on all the Web Services of the list with no prior control or checking for functionality of other relevancy. In this work, beside the criteria of interest, the WS consumer is able to perform a typical WS UDDI based search for a specific functionality. In return the requester gets a “live” and “cross-checked” list of Web Services of interest, accompanied by QoS values. In our case, QoS
Keywords Quality of Web Service, Web Services discovery, Web services QoS.
1. Introduction Web Services (abbr. WS) are one of the most promising technologies in distributed computing that could fully automate all the web operations of business entities [9]. Quality of Service (QoS) is a very important issue in the area of Web Services since it gives a way to distinguish and rank services with similar functionality. The aim of this work is the development of a transparent combination of traditional Web Service discovering methods enhanced with QoS enabled characteristics. The key concept in the design and implementation is to maintain all compatibility features with the standard WS searching mechanisms and expand them to support QoS characteristics. Taking advantage of the utilization feedback and evaluation, querying for Web Services becomes more efficient than standard keyword searching, since there is a measure for comparison of similar Web Services. A WS consumer may select among services the one that suits him/her needs most and furthermore refine
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Department of Computer Engineering & Informatics School of Engineering, University of Patras Rio Campus, 26500 Patras, Greece
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characteristics are produced dynamically, depending on the search’s criteria.
4. QoSPublish and QoSFeedback: These Web Services offer respectively to the provider and the user the possibility to import their own values for the metrics of a Web Service.
3. Solution Overview A UDDI search wrapper is introduced to facilitate the traditional WS discovery taking into account QoS characteristics in a transparent way. The solution, which is called “Search Web Services Plus QoS”, is designed to be provided as a service-library that facilitates an alternative way of discovering Web Services. Overall, to implement and evaluate the proposed mechanism, we created the components presented in the following operational diagram (Figure 1).
5. TestFindQoSService and TestPublishFeedback: Finally, these two assessment/experimental applications, which are not presented in the above diagram, were created to test the Web Services that are mentioned above. Details are discusses in section 6.
4. Architectural Approach In this section further details concerning the players of the proposed solution are discussed. Operation and architectural diagrams outline the workflow of functions and sub-mechanisms. 4.1 QoSdatabase (QoS metrics subsystem) Though the total of metrics is a predefined limited set, the model introduced is able to accept extensions of more metrics plus the corresponding category description and grouping information, without complications in existing applications that use them already. 4.2 Workflow of WebServicesQoS The core mechanism included in our approach is called WebServicesQoS. It is a service that allows a WS consumer to search for Web Services of a particular functionality and QoS characteristics. The requester or the provider submits requirements/ preferences and the mechanism queries the UDDI catalogues, based on these criteria. Following, it evaluates the QoS of each web service returned, based on the metrics’ values that are stored in the database and returns the results to the requester or the provider.
Figure 1: Outline of architecture diagram
1. QoSDatabase: This is the main storage database system that contains all the metrics definitions. Corresponding values for each Web Service are also supported by the system for the case of UDDI servers that do not support QoS property storage.
4.3 Search Web Services Plus QoS This is a second flavor of the previous service that supports multiple UDDI registries for queries as well as an arbitrary number of criteria types to query for besides the WS key.
2. WebServicesQoS: This application gives the requester the possibility, to define a keyword and discover in a predetermined UDDI catalogue all the matching Web Services. The additional possibility of this application is that apart from the UUID of each Web Service, a value of the QoS is also returned as it is calculated by the algorithm in [1] according to the results of the discovery. The requester also has the option to determine the categories on which he wants to focus, as for example the price and the reputation.
The operation of Search Web Service Plus QoS Web Service appears in the following diagram (Figure 2). The requester or the provider, via the Search Web Service Plus QoS web service, sends part of the WS description, preferences and any of the extra criteria included in a typical WSDL description. The consumer may also select the UDDI catalogues where the discovery will take place in order to broaden the results set (when choosing a large number of registries) or minimize the response time (by choosing registries close to his/her infrastructure). Afterwards, the service performs discovery in the predefined UDDI catalogues, based on these criteria. Finally it evaluates the QoS of each web service returned,
3. Search Web Services Plus QoS: This Web Service executes precisely the same operation as the previous one. The difference is that more criteria can be imported for the search, such as the BusinessKey and the TModel, as well as the UDDI catalogue in which the search will take place.
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Moreover, consumers’ evaluation is only accepted to QoS characteristics that have the evaluation feature enabled by the provider.
based on the metrics’ values that are held in the data base and returns ranked results to the requester or the provider.
6. Evaluation Experimentation – Simulations To evaluate the functionality, feasibility and effectiveness of the mechanism proposed, a number of tester applications have been developed. In the following, details and snapshots of testing applications are provided for the discovery services as well as the user based feedback about a consumed WS mechanism. 6.1 WebServicesQoS assessment application The assessment application utilizes the online http://test.uddi.microsoft.com UDDI catalogue [10] for the discovery and then returns the UUID and the value of the QoS for each Web Service found, on screen (Picture 1). The QoS value is calculated according to the enhanced algorithm where null QoS values are overridden. We have provided a simple interface for a UDDI QoS search frontend in accordance to the MS public UDDI implementation. In our case a consuming user may also select the quality criteria which he/she wants to define as those of the most importance.
Figure 2: Architecture diagram of web application WebServicesQoS
5. Implementation Issues All the applications have been implemented under the Microsoft Visual Studio .NET 2003 environment, while the database has been deployed on Microsoft SQL Server 2000. Testing and experimental evaluation were conducted in an Intel Pentium 4 2.60GHz using 512MB of RAM with Microsoft Windows 2003 Server and Microsoft .NET Framework version 1.1 installed. The proposed mechanism is independent of the specific implementation choices, which have been made in order to take advantage of the authors’ previous experience in the field of WS selection mechanisms (see related work in [1], [6], [4]).
6.2 TestFindQoSService To test and assess functionality of Search Web Service Plus QoS, a web application, named TestFindQoSService, was used. The RetrieveGroups method is called at first and the list of the groups appears on the screen.
5.1 QoSDatabase (QoS metrics subsystem) For the experimental evaluation, we used the metrics presented in [1]. However, our mechanism and in particular the QoS metrics subsystem implements a scalable and extendible schema to store any number of different metrics. 5.2 Search Web Services Plus QoS The class QoSFindService provides standard findservice properties and methods extended to support QoS. A subtle difference is that the method Sent has been modified suitably to return a modified ServiceList which also shows the QoS for each Web Service. 5.3 QoSPublish and QoSFeedback To feed metrics’ values for a Web Service either by the provider or the evaluating user, two Web Services are provided. The QoSPublish Web Service gives the possibility to the provider of a Web Service to define his own metrics and metrics’ values for this Web Service.
Picture 1: WebServicesQoS testing application's interface after discovery completion
After inserting the keyword “cardvalidation” in the textbox and, in design or automatically before execution time, setting in this case a single UDDI catalogue http://test.uddi.microsoft.com, the QoS preferences and also a business key as an extra criterion for a second call of the FindQoSService.
The QoSFeedback Web Service gives the opportunity of evaluation (i.e. metrics feedback value) to the end user. Consumers do not affect the metrics’ type or description.
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of the mechanism in order to support semantic based discovery for annotated WS descriptions is an additional challenge following ideas and metrics proposed in the work of [6]. Interesting WS discovery ideas have been presented in the work of [4] and [8] for P2P discovery. Extending these proposals to support QoWS in a dynamic and distributed registry of WS is also particularly motivating.
6.3 TestPublishFeedback To assess the proposed Web Services QoSPublish and QoSFeedback, an application scenario, named TestPublishFeedback, was implemented. The application has an interface (Picture 2) where the ids and the names of the metrics appear and where the user can define the metrics’ values of his choice. The tester application has been available for evaluation online in laboratory environment. A group of software developers and students have verified the proposed mechanisms functionality by issuing their own queries and applying at will WS discovery with QoS characteristics. Summarizing, the evaluation scenarios have been successful and the evaluating group verified the functionality, scalability and effectiveness of our approach.
8. References [1] J. Garofalakis, Y. Panagis, E. Sakkopoulos and A. Tsakalidis, “Contemporary Web Service Mechanisms”, in Journal of Web Engineering, 2006, vol 5, to be published. [2] Y. Liu, A.H.H. Ngu, , L. Zeng, “QoS Computation
and Policing in Dynamic Web Service Selection”, in proceedings of the WWW2004, New York, USA. pp. 66-73. [3] C. Makris, Y. Panagis, E. Sakkopoulos, and A.
Tsakalidis, “Efficient and adaptive discovery techniques of web services handling large data sets”, in J. Systems and Software, Elsevier Science, to be published. [4] C.
Makris, E. Sakkopoulos, S. Sioutas, P. Triantafillou, A. Tsakalidis and B. Vassiliadis, "NIPPERS: Network of InterPolated PeERS for Web Service Discovery", in the proceedings of the 2005 IEEE International Conference on Information Technology: Coding & Computing (IEEE ITCC 2005), Track Next Generation Web and Grid Systems, Full Paper, Las Vegas, USA, pp. 193-198.
[5] D. A. Menascè, “QoS Issues in Web Services”, IEEE Internet Computing, vol. 6 (6), 2002, pp. 72-75.
Picture 2: TestPublishFeedback application's interface
7. Conclusions And Future Steps
[6] S. Ran, “A model for web services discovery with
This work provides an integrated solution for QoS based WS discovery in generic existing UDDI compatible catalogues. We describe a mechanism for discovery in a generalized environment that stores a dynamic number of groups/ categories of different Web Services. Moreover, we have proposed a dynamic schema that supports an arbitrary number of different QoS metrics without affecting the discovery methods themselves. We have implemented the proposed UDDI search wrapper to take into account possible QoS characteristics available in transparent way. To verify the functionality and experiment on the effectiveness of the mechanism proposed, a number of testing demonstration have been implemented. We have received encouraging feedback from software developers that evaluated our mechanism implementations. Future steps include the incorporation of this wrapper into a broker based WS selection infrastructure to facilitate QoS enabled discovery. Furthermore, extension
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qos”, in SIGecom Exch. 4 (1), 2003, pp. 1-10. Sakkopoulos, D. Kanellopoulos, and A. Tsakalidis, “Semantic Mining and Web Service discovery techniques for media resources management”, in the International Journal of Metadata, Semantics and Ontologies (IJMSO), Vol. 1 (1), Inderscience Publishers, to be published.
[8] C. Schmidt and M. Parashar. “A peer-to-peer
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Server 2003 UDDI Services. URL: http://www.microsoft.com/windowsserver2003/ technologies/idm/uddi/default.mspx
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