Research On The Approach Of Service Selection In Grid Workflow

With the development of the grid and related technology, more and more persons andenterprises start to implement their business process by using some resources, which belong toother organizations. Owning to its complexness, the traditional approach that user still need toessentially compose detailed workflow descriptions by hand can't satisfy the requirements thegrid application in reality. So grid workflow, which based on the traditional workflowtechnology, is put forward amid to automating the business process in grid envirmonent.Considering the advantage such as loose coupling, quick response and etc, which can beachieved by adopting Service-Oriented Computing paradigm, we utilize the service to refer tothe activity in workflow and take the service selection problem as our main research content.As far as service selection problem is concerned, most of the current researches putemphasis on interface matching, which can't reflect its characteristic .In this paper, we proposala constraint driven selection approach, which take all kinds of constraint from the user andprovider, function and non-function, single service and workflow into account. The mainresearch work which assume the candidate services have met the requirement of interfaceinclude:1. A formal model that describes the non-function property of service is put forward. As abridge, this model provides a foundation to compare the user's requirement to NFP and serviceattribute. In this model, not only the value range of a property but also the relationship amongseveral properties can be described, which improve its express ability greatly. As for differentkinds of value, we propose the corresponding description format that matches its feature.2. Based on the non-function property model, we define the respective forms of constraintfor the user and provider. In order to handle them easily, we classified users' constraints intoobliged, reference, single service and multi-services one. Through an example of workflowquality, we also show the way to convert the constraints from an implied form into clear one.The constraints of single service kind are handled by adopting set theory while the multi-serviceconstraints are reduced to a constraint satisfaction problem.In matching algorithm, we devise a two-level approach that considers the different priorityof all kinds of constraints. By this way, we can satisfy the requirements of both the singleservice and the whole workflow, which won't badly reduce the performance of the algorithmeither.3. As to some large granularity and state-maintaining services, their dynamic feature offunction known as protocal should also play an important role in service discovery. To modelthe protocal, we adopt a revised deterministic finite state automation provided with a first in andfirst out message queue. Through the queue, we realize the asynchronous commucation betweenthe services in the model, which improved the recall factor of the service selection approach.Based on the analysis result of the complete execute path in the DFA, we provide the concretealgorithm on how to test the compatibility and substitution relationship between service, whichsolved the requirements both from clients and other service in the workflow. Considering thefact that there are many business standards about service protocols now, we describe theapproach how to transform the protocal from the standard form into DFA by the example ofBPEL, which will enhance the practicality of our approach greatly.From the view of the difference between service and traditional component, the approachof service selection advanced in this paper put emphasis on the non-function property andservice protocols, which are often ignored in current researches.