Author Topic: An Innovative (QOS) based Service Selection for Service Orchrestration in SOA  (Read 2353 times)

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An Innovative Quality of Service (QOS) based Service Selection for Service Orchrestration in SOA
Author : S.Neelavathi, K.Vivekanandan
International Journal of Scientific & Engineering Research, IJSER - Volume 2, Issue 4, April-2011
ISSN 2229-5518
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Abstract— Service Oriented Architecture (SOA) has become a new software development paradigm because it provides a flexible framework that can help reduce development cost and time. SOA promises loosely coupled interoperable and composable services. Service selection in business processes is the usage of techniques in selecting and providing quality of services (QOS) to consumers in a dynamic environment. Single business process model consists of multiple service invocations forming service orchestration. It represents multiple execution paths called modeled flexibility. In certain cases, modeled flexibility can cause conflicts in service selection optimization, making it impossible to simultaneously optimize all execution paths. This paper presents an innovative approach to service selection for service orchestration that addresses this type of conflicts by encompassing status identification based availability estimation with multiple QOS constraints along with an effective quality assessment model. This model captures the expectations from the users on the multiple quality of a service and returns ratings as a feedback on the service usage. This updated rating in the service list can be used by the new user. This proposed method provides optimal services to users consistently and efficiently thereby resulting in more meaningful and reliable selection of services for service orchestration in SOA.

Index Terms— Service Oriented Architecture, Service Selection, Service orchestration, Meta-metrics, Modeled Flexibility, Rating, Multiple QOS level, local selection, global selection.

Service oriented architecture (SOA) is a new para-digm for software development that promises loosely coupled, interoperable and composable components called services.  Service orchestration is the execution of a single transaction that impacts one or more services in an organization. It is called as business process. Business processes are implemented by orchestrating services of different activities involved in it. Multiple QoS-based service selection results in selecting an optimal service for single activity from a set of candidate services, thereby maximizing the QoS of the entire business process. A single business process model can represent multiple execution paths known as modeled flexibility. Modelled flexibility can cause conflicts in service selection if the different optimal services are selected for the common activity in both the execution paths thereby making it impossible to optimize all execution paths.  The proposed approach to service selection addresses this type of conflicts through a set of meta-metrics (probability of execution).

Status identification based availability estimation for service selection is used along with multiple QoS con-straints. It is extended with an effective quality assess-ment model that is used to match the expectations from the user with that of rating of services held in service list. The service list is divided into four groups with all the services having the triple factor of quality rating for all the multiple QoS constraints.  The feedback from the user after service usage is used to update the service list. This proposed approach of service selection with multiple QoS factors results in more meaningful and reliable selection of services used in service orchestration in service oriented architecture. Along with this, it also resolves the conflicts with modeled flexibility in business process by meta-metrics thereby ensuring selection of optimal services for all the service invocations.

The service orientation and Service Oriented Ar-chitecture (SOA) are not new or revolutionary concepts. It is the next stage of evolution in the distributed computing [2]. SOA is not a Technology and is only an architectural approach. SOA is defined as “Service Oriented Architecture (SOA) is a paradigm for organizing and utilizing distributed capabilities that may be under the control of different ownership domains [2].” SOA includes the previously proven and successful elements from past distributed paradigms. These elements are combined with the design approaches to leverage recent technology in distributed computing [1].
In SOA, the loosely coupled systems do compu-ting in terms of services. SOA separates functions into distinct units, or services, which developers make accessible over a network in order to allow users to combine and reuse them in the production of appli-cations. These services communicate with each other by passing data from one service to another [3], or by coordinating an activity between two or more services. They use the well established standards [4].
This approach  is based on the design principles of loose coupling, which is a principle by which the con-sumer and service are insulated from changes in underlying technology and behavior, Interoperability[2]  the principle which provides the ability to support consumers and service providers that are of different programming languages on, different operating systems with different communication capabilities, Encapsulation that allows the  potential consumer to be  insulated from the internal technology and even the details of behavior of service, Discoverability which is used to realize the benefit of reuse [5]. Seamless integration of various systems allows data access from anywhere anytime, thereby providing services to customers and partners inside and outside the enterprise. It provides a simple scalable paradigm for organizing large networks of systems that require intero-perability and develops systems that are scalable, evolvable and manageable and establishes solid  foundation for business agility and adaptability.                                                                                                             

2.1 Services In SOA
The most fundamental unit of service oriented solution logic is the service. Services in SOA comprises the below 8 distinct design principles.
   Standardized service contract
Services express their purpose and capabilities via a service contact. It is the most fundamental part of service-orientation.
   Service Loose Coupling
Coupling refers to the number of dependencies be-tween modules. Loosely coupled modules have a few known dependencies whereas tightly coupled have many unknown dependencies. SOA promotes loose coupling between service consumers and providers.
   Service Abstraction
This emphasizes the need to hide as much of the un-derlying details of a service as possible to preserve loosely coupled relationship.
   Service Reusability
The same services can be reused in multiple applica-tions. The agnostic nature of services enables them to be recombined and reused in different forms.
   Service Autonomy
Services to carry out their functionalities consistently and reliably, needs to have a significant degree of control over its environment and resources.
   Service Statelessness
Services are designed to remain stateful only when required. If there are stateful, then the management of excessive state information can compromise the availability of the service.
   Service Discoverability
Service discovery is the process of discovering a service and interpretation is the process of under-standing its purpose and capabilities.
   Service Composability   
It is related to its modular structure. It is com-posed in three ways. Application is an assembly of services, components and application logic that binds functions together. Service Federation is the collection of services managed together in a large service domain and Service orchestration is execution of single transaction that impacts one or more services in an organization.

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