INFORMATIO
WebServices.pdf

Problems like scalability availability and security

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centralized, whereas the participating services are distributed and autonomous. Problems like scalability, availability and security exist on centralized approaches. Peer-to-Peer techniques are attractive for executing services. The most existing techniques implements local selection strategy , meaning that they assign a component service to an individual task one at a time [2],[19]. As a result, these approaches are not able to handle global user constraints and preferences. In order to overcome these limitations the new global planning approach is introduced. In this approach, quality constraints and preferences are assigned to composite services rather than to individual tasks within a composite service. Service selection is then formulated as an optimization problem and a linear programming method is used to compute optimal service execution plans for composite services [1]. This approach doesn’t require any additional functionality and agree with Web services protocol stack capacities. It allows extending the current model by enabling selection of Web Services considering not only functional but also the quality characteristics of elementary Web Services. The detailed description is given in the section 3. 2.3.4. Invoking Web Services using Mobile Agents In Agent Based approaches the accent is made on execution of composite Web Service in a dynamic environment with help of Mobile Agents [7],[8]. In a dynamic environment, it is recommended to decompose the planning process into several steps, each step to take care of a portion of the plan that is under development. When a portion of the plan is finished, it is immediately submitted for execution [8]. A Mobile Agent (Software Agent) is a piece of software that acts autonomously to undertake tasks on behalf of users [8]. The design of many agents is based on the approach that the user only needs to specify a high-level goal instead of issuing explicit instructions, leaving the how and when decisions to the agent. A Mobile Agent exhibits a number of features that make it different from other traditional components including autonomy, goal-orientation, collaboration, exibility, self- starting, temporal continuity, character, communication, adaptation, and mobility [8]. For the agentification of Web services an agent-based multi-domain architecture is used (Fig. 2.2) [8]. Two types of domain exist: user-domain and provider-domain. Two types of agents are considered in the agentification process of an environment of Web services: user-agent act on behalf of users provider-agent act on behalf of providers who manage Web services. In Fig. 2.2, the user-domain has a service-zone and a working-zone. The service-zone has a dedicated portal from which composite services are developed and deployed. In addition, the service-zone has a pool from which user-agents are created. For their installation, user-agents are initially located in the working-zone of the user-domain. User-agents are mobile and thus, have the capacity to migrate from one domain to another. When a user selects a composite service, a user-
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  • Winter '15
  • MAhmoudali
  • World Wide Web, Web Services, Business process modeling, Web Services Description Language

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