13-05-2013, 03:25 PM
AN INTELLIGENT WATER DROPS ALGORITHM BASED SERVICE SELECTION AND COMPOSITION IN SERVICE ORIENTED ARCHITECTURE
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ABSTRACT
Web services are defined as the pieces of software components, which are distributed over the internet
using some standard protocols. With more and more web services become available, QoS is a decisive
factor for selecting the most suitable service from a set of candidate services with the identical
functionality. Thus the approach about the computation of the QoS is also becoming more important in the
service selection. In this paper, we use an algorithm called “Intelligent Water Drops” or IWD algorithm
which is inspired from natural science. It is based on the processes that happen in the natural river system.
The actions and reactions that take place between the water drops are also considered. The river often
chooses an optimal path regarding the conditions of its surroundings to get its ultimate goal, which is often
a sea. These ideas are embedded into the web service selection and composition for providing efficient QoS
web services. This proposed algorithm provides better computing performance than Particle swarm
optimization algorithm (PSO).
INTRODUCTION
A service is a sequence of activities of more or
less intangible nature that normally take place
interaction between customer and service system of
the service provider, which are provided as solution
to the customer problems.[1].A service provider
offers the service and a service consumer utilizes
the service in service oriented architecture[2].
Web service is typically a web application
programming interface that is accessed via HTTP
and executed on a remote system, hosting the
requested services, composing atomic web services
to provide the value added service. Web service
composition attracts wide spread concern, because
more and more organization provide their business
in the form of web service.
Web Service Selection and Composition
In a Composed web service, in addition to QoS of
individual services, the overall aggregate QoS of
the composite service should also be considered.
Web service selection is the selection of particular
web service based on the QoS factors.
Service composition involves the development of
customized services often by discovering,
integrating and executing existing services. It is not
only about consuming services, but also about
providing services.
Web service composition framework is in high
level abstraction, without considering a particular
language, algorithm used in composition process. A
web service can be accessed in a transparent way
through messages by standard tools like SOAP,
WSDL and UDDI.
Non Functional Properties of Web Services
The non functional properties of a web service are
basically classified into the following categories.
Availability: The availability of a service refers to
the probability that the service is accessible.
Execution Time: The execution time of a service
refers to the time span from the moment that
service requester sent the request to the moment
that the service executed result returned.
Reliability: The reliability of a service refers to the
probability that the service returned the correct
result to the user’s request.
Execution Price: The price of service refers to the
fee that the service requester needs to pay for using
the service [4].
Web Service Composition Problem
Consider a travel plan application domain.
The travel may propose the following lists of
activities:
The travel may be a holiday or a business
assignment scheduled for a week. The traveler may
possibly leave on any day.
Stay around some days in hotel.
Based on the distance from the airport to hotel,
make a decision on whether by taxi to hotel.
This task is far trivial as it involves many services,
including the booking of flights, hotels and cars and
it requires a lot of co ordination among these
services.
The traveler decides to schedule the travel plan
through an agent using web services to have a
better control of the budget.
PARTICLE SWARM OPTIMIZATION
ALGORITHM ON WEBSERVICE
Particle Swarm Optimization (PSO) algorithm can
be used to resolve this problem of optimal service
selection. It is the collection of particles that move
around the search space.
In this algorithm, the parameters are initialized.
And then calculation of fitness value is calculated
based on quality factors such as availability,
reliability, cost and execution time.The evolution
only looks for the best solution.
All the particles tend to converge to the best
solution quickly and then update the particle
position and velocity. Figure 2 provides the steps of
PSO algorithm. First, initialize all particles with
random position and velocity vectors. For each
particle’s position, evaluate the fitness value.
EXPERIMENTAL RESULTS
The QoS-based service selection problem involved
in service composition is, how to select one service
for each involving task from its corresponding
existing candidate service group, so that the overall
QoS of the constructed composite service can be
maximized. The values for QoS parameters are
randomly chosen for the first time and updated on
every single evaluation. For the evaluation process
three abstract web services and four candidate web
services for each web service are considered.
Figure 3 shows the full work flow of this paper.
The most suitable web services will be retrieved
from the database, based on the fitness value.
Design of the database includes the values assigned
for each parameters of the candidate web service.
The parameters considered for evaluation are price,
response time, availability and reliability.
CONCLUSION
With the increasing of the number of web
services, it is necessary to solve the problem of
service selection of meeting users need in the web
service composition .Web services composition is a
new software development paradigm, and it is a key
point to achieve service oriented computing
currently. For meeting the QoS requirements of
consumers, In order to solve services composition,
PSO algorithm and Intelligent Water Drops
Algorithm are used. To verify the best web service
decomposition algorithm, these above two PSO and
IWD are compared. The experimental comparison
result shows that, the Intelligent Water Drops
Algorithm is the best algorithm for web service
composition. From that, the IWD algorithm having
the higher correctness value, feasibility, and
effectiveness than the existing PSO algorithm.
Computational overhead for service composition
with more than 50 services is left behind for future
work.