We propose a technique for dynamic selection of Web Services which will also handle the problem of redundant Web Services. In this work, we introduce a model with a Web Service repository, as shown in figure 3.1 will act as an independent unit possessing a definite functionality. This repository will be used to redirect the client’s request. This will also provide a level of security since it will not be allowed to invoke directly by the clients. This technique will prevent unauthorized access to the real services. This provision will also help to hide the systems complexity from the clients.
The repository will perform three functions namely, storing, collecting and reasoning. In storing operation a QoS feedback report is generated by the client and is saved in the repository. The QoS feedback report provides a historical reference for the consumer to assess the provider. Each provider only keeps the feedback information relevant to it. The collecting operation retrieves all necessary data from providers for the reasoning operation. The reasoning operation manages to select the best service provider for the consumer according to the collected data. Consider an example where clients needs the services (S1,S2) as in fig.3.1, it sends a request .The collecting, storing and reasoning mechanism interacts with the web services to find the most appropriate of the services and the results are stored in the repository for future reference. Web Services here interacts with the reasoning mechanism to find out the appropriate services. Once the service is selected, the
Figure 3.1: Repository based Web Service Selection
request is forwarded to it. Finally, when the result is generated, it is passed to the repository which sends it back to the client.
3.2.1
Algorithm: Selection of Service
This algorithm shows the necessary steps to choose a service and get the maximum quality results.
1. For finding a service for a specified task, perform a search on service descrip- tions.
2. Arrange all discovered services by their signature parameter and discard all other services.
3. Get the desired Service Parameters.
4. Collect the services result and order by their utility.
Figure 3.2: Selection Process
This algorithm provides an approach for selecting a specified service. Services, not matching the profile are discarded on the fly .It also helps in taking an alternative services.
3.2.2
Design of the Proposed Architecture
This section provides an overview of the design of the simulation model that is used to evaluate the RBWSS(Repository Based Web Services Selection) approach. The architecture, proposed here consists of three main components - Clients, Reposi- tory Layer, and Web Services, forming the key compound objects of the high-level view of the simulation design. Object LG (load generator) generates clients’ re- quests (entities); object represents the behavior of the model, and each object WS corresponds to a Web Service. Object LS (load sink) is used as the end point of the entity flow. It accepts the incoming from the RBWSS entities and disposes of them.
The simulation design of the model is presented in figure 3.4. Component Manager is not included, since the settings of the reasoning mechanism are defined before the simulation runs. There is a Virtual Web Service corresponding to each group of redundant services with particular functionality. The reasoning
mechanism is presented by a queue and a server.
3.2.3
AnyLogic Enterprise Library
AnyLogic provides libraries for simulating systems in various domains. The enter- prise Library can be applied in discrete systems, such as manufacturing, services, business processes, etc. [13]. It is able to ”create flexible models, collect basic and advanced statistics, and effectively visualize the process”, in order to represent the system. At the same time, it ”provides a higher-level interface for fast creation of discrete event models in the style of flowcharts”, using objects like source, sink, queue, and delay server, and others, in a drag-and-drop manner [14] .Entity is a basic concept in the Enterprise Library. The entities represent individual units that are evaluated in the simulation. They can enter and leave objects through one directional port. The connections between the ports are established by connectors.
3.2.4
Evaluation
This section describes the evaluation of the proposed Repository Based Web Ser- vice Selection (RBWSS) approach. Firstly, a feasibility check is done to determine whether it is possible to build such architecture. Secondly, the behavior of the Web Services is observed and analyzed in different environments. Finally, to observe the behavior of the prototype with different selection techniques, the simulation method is used, since the study of the optimal strategies is difficult in a real environment where there are many uncontrollable parameters.
Figure 3.4: Selection Process
The evaluation process carried out by analyzing the RBWSS prototype in or- der to test whether or not the architecture is a feasible technique for managing redundant Web Services on the server side in a dynamic and transparent manner. A simplified prototype of the proposed architecture is developed, in order to ob- serve if the model is an applicable approach for dynamic selection of redundant Web Services. The dynamic service selection is realized by reflection that allows us to obtain information at run-time about methods, constructors, and instance fields of classes, as well as to invoke them dynamically [15], [16].
The reasoning mechanism is based on a random selection technique that does not require any information about the services. Since the decision is done in a random manner, there is no need for selection criteria, neither the data about the services must be collected and aggregated by the model. The model of the reasoning mechanism contains only the WSDL descriptions of the redundant Web Services.