READIT - 2009 - Indira Gandhi Centre for Atomic Research

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Proceedings of READIT-2009, Kalpakkam - 603 102, 29-30 Dec 2009 web services reflect preconditions and effects through OWL ontologies. These comparative strategies are discussed in the sixth section. The seventh section concludes with future enhancements. 2. EXAMPLE SCENARIO To understand service composition a web service scenario for booking in a travel package from a travel agency is considered. We can see that a closed-world travel example evolves into a dynamic integrated solution [4]. In a closed-world case the customer talk to the travel agent who notes the customer request and generates a trip request document that may contain several flight and hotel reservation. When done the agent puts the request in cancelled or completed request database. The completed document is sent to the customer as response. If cancelled the customer is intimated and the customer re-iterates. In the open-world variant let us imagine that the travel agent wants to cooperate with external specialized service providers that offer hotel and flight reservations. Upon receiving the customer’s request the agent will create a trip request and derive the required hotel and flight reservation. Processes can spawn off other processes at run-time. 3. DEFINITION The process of creating composite services by composing web services is called service composition. Composition involves invoking several services and combining their functionality. The business logic of the client is implemented by composing several services. Service composition is performed by composing elementary or composite services. Service composition modeling can be done in six different dimensions. A component model is a basic assumption. An orchestration model uses process-modeling languages like UML activity diagram, Petri-nets, state-charts etc. Data and data access model define how data is specified and exchanged between components. The service selection model deals with static and dynamic binding. It deals with how a web service is selected as a component. A component can be statically selected at design-time or dynamically selected at run-time. Transactions model define which transactional semantics can be associated to the composition and how this is done. The composite service must work without aborting during execution. The exceptional states must be handled with an exceptional handling model. 4. COMPOSITIONAL ISSUES Web service composition in itself poses as a complex and challenging. There are six major issues that have a huge impact on service composition. These issues are discussed below. Coordination – When web services are composed to build composite applications coordination of sequences of operations are needed to ensure correctness and consistency. Transaction – Over the coordination framework a transaction protocol should be added to ensure ACID properties of web service transactions in the long running business activities. Context – Context is the information utilized by the web service to adjust execution and output to provide the client with customized and personalized behavior. Context contains information like customer’s name, address, current location, the type of client device and preferences regarding communication. 75 2
Proceedings of READIT-2009, Kalpakkam - 603 102, 29-30 Dec 2009 Conversation Modeling – Developers must be supported in defining service models and richer web service abstractions. Completion abstractions contain compensating operations in case a forward operation has been cancelled. Activation abstractions describe implicit and explicit transitions between states. Conversation model facilitates service discovery, dynamic binding, service composition model validation and service composition skeleton generation. Execution Monitoring – There is centralized and distributed execution of composite web services. Centralized execution is like client-server paradigm. The server is like a central scheduler that controls execution of components of a composite web service. A distributed paradigm has participating web services share their execution context. To guarantee correct order of execution the each of the host running a web service has its own coordinator which collaborates with other coordinator. Infrastructure – 1.48% of UDDI entries are unusable [5]. They contain broken or inaccurate information and missing pointers. Service discovery in UDDI is limited to functional requirements. An extended service model adds another entity called ‘QOS certifier’. The service provider should provide QOS information apart from functional aspects. The certifier must approve the claim of the provider. The service consumer makes a finer search by adding QOS requirements. The user can also consider a trade-off by reducing the QOS constraints in case no services match the QOS constraints. This extension achieved by adding an element to the UDDI DTD called ‘qualityInformation’. The QOS aspects include availability, reliability, performance etc. 5. COMPOSITIONAL APPROACHES Web service composition refers to the integration of more than one web service to realize business functionality. Compositional approaches are categorized into five categories. Based on web service composition time static or dynamic composition can be done. There are other compositional strategies like model driven service composition, business rule driven service composition, declarative service composition and automated / manual composition [6,7,8]. Static / dynamic service composition – The architecture and design of the software system is planned at design time. Static composition is done at design time. The components to be used are chosen, linked, compiled and deployed. The service selection is done priori and manually. When the business partners rarely changes in the composite application static composition holds good. There are possibilities when the business partners change or old services must be changed by new services. New services become available. Service processes should transparently adapt to environment changes or customer requirements. Components should automatically adapt to unpredictable changes. Thus dynamic service composition is needed for runtime composition of web services. Model driven service composition – Process flows are described using business rules. Service composition is like workflow. A business function is represented by a series of logically related activities performed together to produce a defined set of results. Service composition element is based on business process elements activity. Service composition is represented by a business function which is the condition. Pre and post conditions constrain the behavior of composition which is the event. Service composition is represented by flow. The flow describes block of activities as messages. The provider provides role as concrete services and abstract class. Process is the party participating in service composition. 76 3
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National Conference on Recent Advan
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Foreword The 7th biennial national
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access to information resources. RF
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Organising Committee READIT-2009 Ch
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Invited Presentations: CONTENTS Ses
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C. Jaykumar, E. Soundararajan, V. R
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Session-I: Semantic Web Technologie
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Proceedings of READIT-2009, Kalpakk
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Session-III: Open Source Solutions
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Session-IV: Knowledge Management Pr
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upon by indwelling and is the basis
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new, and its combination of new ide
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o Knowledge: Both explicit and taci
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Knowledge Management Practices in L
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To these paraphrases of Macintosh
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(iii) Healthy interactions among pr
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9. CONCLUSION Knowledge management
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Ontologies define a common vocabula
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to have an environment that allows
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CDPS PC System Based SS-I SS-II RAA
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Preservation of Manuscripts with Sp
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- (Many more) 3 Chemical Factors a.
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6.2.2 Software The Softwares requir
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7.1.3 Current Work As the above pro
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Treatment process 7.2.6 Drying Afte
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Before Editing & Cropping After Edi
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Knowledge Management - An Organizat
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5. KNOWLEDGE MANAGEMENT ACTIVITIES
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Management System and is made avail
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Services 3.0 make it easier than ev
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ecover data when a disk fails and r
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Symmetric Multi Processing (SMP) Se
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Knowledge management practice in li
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3. KNOWLEDGE MANAGEMENT: SOME DEFIN
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It is to create a set of effective
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REFERENCES 1. Banka Bihari Chand (2
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2 Fig : 1. Five ‘ C ‘ Model Kn
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4 Knowledge acquisition is the star
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6 group of audience. Similarly wit
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8 Knowledge sharing is enhanced by
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10 sharing, and creating a map of
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12 10. REQUIRED SKILLS AND CAPABILI
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14 Wireless Communication, Networki
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READIT - 2009 - Indira Gandhi Centre for Atomic Research

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