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DEBREMARKOS UNIVERSITY
COLLEGE OF TECHNOLOGY
POSTGRADUATE PROGRAM IN SOFTWARE ENGINEERING
Article Review on:
Towards Scalability of Reputation and QoS Based Web Services Discovery
Using Agents and Ontologies
Authors:
Rohallah BENABOUD, Ramdane MAAMRI and Zaïdi SAHNOUN
REVIEWED BY:
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SUBMITTED TO: ---
Submission Date
DEBREMARKOS, ETHIOPIA
Background
There is not any unified description for Web Services. However, a Web Service is a service-
oriented web application that provides a web API (interface) that is well defined using an XML
based document WSDL (Web Service Description Language), and enables other applications to
bind to it via URLs and internet based protocols, and communicate to using XML based
messages using SOAP. It is a software system designed to support interoperable machine-to-
machine interaction over a network. There are two major classes of Web services, REST-
compliant Web services, in which the primary purpose of the service is to manipulate XML
representations of Web resources using a uniform set of "stateless" operations; and arbitrary Web
services, in which the service may expose an arbitrary set of operations.
Now a day's research done have focused on performing semantic matching to enhance the
accuracy of Web service discovery. Although the use of ontologies, machines or programs are
still not efficient enough to take the automatic and dynamic decision for semantic Web service
based service discovery, selection and invocation with the help of software agents, information
provided by Web services can be made more efficient and more dynamic. Software agents are
now increasingly used in commercial applications to solve complex engineering problems, for
their autonomous, proactive and social capabilities.
Problem addressed (Statement of the problem)
With an expanding of Web services giving same functionalities, non-functional properties like
Quality of Service (QoS) and reputation are becoming an important criterion for selection of the
best available service. A major problem in using QoS for service discovery is the specification
and storage of the QoS information. As, currently, the growth of web service technologies
becomes rapid, discovering web services is the most urgent problem to be solved; which is
finding web service provider locations which satisfy specific requirements. Web services are
important only when they can be discovered, otherwise they are useless if they cannot be
discovered. So, discovery is the most important task in the Web service model.
Objective of the study
The study is conducted on development of an agent based framework for Web services discovery
and selection in which, ontologies are used to describe Web services, QoS and customer’s
requirements.
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The specific objectives of the study are: (i) to present a framework for Web services discovery
and selection based on intelligent software agents, OWL-S and domain ontologies , (ii) to
discover web services in much higher successability while keeping the lower response time by
exploiting the parallelism and the distribution given by agent technology, (iii) to propose a
simple ontology-based OWL-S extension to adding QoS to Web service descriptions.
Framework of the study
As stated in the article, the authors' new proposed frame work has main rules. Some of them are:
Each Provider Agent implements a number of Web services described semantically with
OWL-S enhanced with QoS attributes.
The central ontologies base will be consulted periodically by Provider Agents to develop
or enrich local ontologies.
Domains Ontologies are obtained and updated periodically using local ontologies in the
reason to ensure the homogeneity.
The central OWL ontologies base contains the different concepts used in diverse fields of
proposed Web services.
Figure 1. Agent-based framework for WS discovery
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Methodology
Web services are described using functional and non-functional properties. Functional properties
of services represent the description of the service functionalities like Service Name, Textual
description, a set of Inputs and a set of Outputs. Non-functional properties represent the
description of the service characteristics (e.g. QoS) which are not directly related to the
functionality provided.
The researchers have done using functional match, calculation of QoS & reputation scores in
matching web service to request which evaluates the similarity between request and Web service
advertisements. Similarity of functional properties, names and textual description, of request and
web services are measured using syntactic similarity function by N-grams methodology.
Furthermore, the set of inputs and outputs in the request & service are calculated by using inputs
similarity and outputs similarity algorithms respectively. The researchers, in finding and
calculating QoS Score and Reputation Score, have used a QoS and reputation score algorithms.
The authors of the article used JADE, a very powerful middleware framework built with Java to
design a MultiAgent Systems based architecture, platform to implement their new framework.
Results Obtained
In the implementation platform, the researchers had made experiments for the purpose of
estimating the performance of their system. They had used four Provider Agents and each one
implements five Web services. As the simulation progresses, new service ratings are generated,
and the service reputation scores become different. Hence, the selected services change. After
100 runs, the experiment has illustrated that the chance of selecting a service, which better meets
the QoS which a service customer was declared as important, is enhanced when previous service
consumers have given a high rating score for the same QoS attribute.
Conclusion
To sum up, when there are many web services that provide the similar functionalities finding the
relevant service becomes a tedious task. Web services are becoming an important technological
component in the application integration domain. Large enterprises are deploying as many as
several thousand Web services, a situation that brings into focus the need for tools to discover
and integrate these services with each other and with the other applications in use . The article
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has introduced a framework for Web services discovery and selection based on intelligent
software agents, OWL-S and domain ontologies. With semantics provided by OWL-S and
domain concepts, match and discovery engine can return the most relevant services.
Future Work
The future work suggested by the authors of the article is to incorporate the Web services
composition into the above proposed framework.
Problem of Future Work
The functionality of a Web service needs to be described with additional pieces of information,
either by a semantic annotation of what it does and/or by a functional annotation of how it
behaves. And hence, this functionality of a web service may probably be a problem for
incorporating web services to the proposed framework for the study.
Suggested methodology for future work
The reviewer of the article believe that any approach for Web Services semantics should build on
the current Web Services standards and allow for using the semantic representation language of
the user’s choice. Standardization in the area of Web Service semantics calls for a careful and
inclusive approach, given the early stage of adoption of semantic representation languages, and
the availability of multiple potential candidates. Also, the approach has to be based on
experience and lessons learned in applying the approach to solve real-world integration
problems.
Importance of solving the problem
The importance of Web services is not that they are new, but that this new technology addresses
the needs of application development. They help to solve the interoperability problem by giving
different applications a way to link their data. Using Web services you can exchange data
between different applications and different platforms. Web services will prove a great
advantage to business, giving a World Wide Web presence all access to a world of computing
power and flexibility. So it’s the time to remain in touch with customers or audiences who can
get maximum benefit through website. Therefore, for these and other roles and benefits of web
service applications, web service compositions with the proposed framework has to be
integrated.
