Specifying QoS properties can limit the selection of some good web services that the user will have considered; this is because the algorithm used strictly ensures that there is a match between QoS properties of the consumer with that of the available services. This is to say that, a situation may arise that some services might not have all that the user specifies but are rated high in those they have. With some tradeoffs specified in form of weight, these services will be made available to the user for consideration. This assertion is from the fact that, the user's requirements for the specified QoS properties are of varying degree i.e. he will always prefer one ahead of the other. This can be captured in form of weight i.e. the one preferred most will have the highest weight. If a consumer specifies light weight for those QoS properties that a web service is deficient in and high weight for those it has, this will minimize the difference between them. Hence the service can be returned.
Deep Dive into Effect of Weighting Scheme to QoS Properties in Web Service Discovery.
Specifying QoS properties can limit the selection of some good web services that the user will have considered; this is because the algorithm used strictly ensures that there is a match between QoS properties of the consumer with that of the available services. This is to say that, a situation may arise that some services might not have all that the user specifies but are rated high in those they have. With some tradeoffs specified in form of weight, these services will be made available to the user for consideration. This assertion is from the fact that, the user’s requirements for the specified QoS properties are of varying degree i.e. he will always prefer one ahead of the other. This can be captured in form of weight i.e. the one preferred most will have the highest weight. If a consumer specifies light weight for those QoS properties that a web service is deficient in and high weight for those it has, this will minimize the difference between them. Hence the service can be returne
Effect of Weighting Scheme to QoS Properties in Web Service Discovery
¹Agushaka J. O., Lawal M. M., Bagiwa, A. M. and Abdullahi B. F.
Mathematics Department, Ahmadu Bello University Zaria-Nigeria
¹jagushaka@yahoo.com
Abstract
Specifying QoS properties can limit the selection of some good web services that the user will
have considered; this is because the algorithm used strictly ensures that there is a match between
QoS properties of the consumer with that of the available services. This is to say that, a situation
may arise that some services might not have all that the user specifies but are rated high in those
they have. With some tradeoffs specified in form of weight, these services will be made available
to the user for consideration. This assertion is from the fact that, the user’s requirements for the
specified QoS properties are of varying degree i.e. he will always prefer one ahead of the other.
This can be captured in form of weight i.e. the one preferred most will have the highest weight.
If a consumer specifies light weight for those QoS properties that a web service is deficient in
and high weight for those it has, this will minimize the difference between them. Hence the
service can be returned.
Key Words: QoS properties, QoS weighting vector, Distance Measure
1. Introduction
Web Services are the third generation web
applications;
they
are
modular,
self-
describing, self-contained applications that
are accessible over the Internet Cubera et al
(2001). A Web Services (sometimes called
an XML Web Services) is an application
that enables distributed computing by
allowing one machine to call methods on
other machines via common data formats
and protocols such as XML and HTTP. Web
Services are accessed, typically, without
human intervention. Web service technology
address
the
problem
of
platform
interoperability however, in the work of
Plammer and Andrews (2001), they showed
that there is actually a slow take off of web
services technology and DuWaldt and Trees
(2002) attributed this slow take off to factors
such as perceived lack of security and
transaction support and also quality of the
web service. Web Services standards like
WSDL
(www.w3.org/TR/wsdl),
SOAP
(www.w3.org/TR/soap2-part1),
UDDI
(www.uddi.org/pubs/uddi-v3.00) and BPEL
(ftp://www6.software.ibm.com/software/dev
eloper/library/ws-bpel.pdf) provide syntax
based interaction and composition of Web
Services in a loosely coupled way that does
not take into account the non-functional
specification like quality of service (QoS)
properties such as scalability, performance,
accessibility etc. QoS for Web services
gives consumers assurance and confidence
to use the services, consumers aim to
experience a good service performance, e.g.
low waiting time, high reliability, and
(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 7, No. 3, March 2010
92
http://sites.google.com/site/ijcsis/
ISSN 1947-5500
availability to successfully use services.
Service registries host hundreds of similar
Web services, which make it difficult for the
service consumers to choose from, as the
selection is only based on the functional
properties albeit they differ in QoS that they
deliver. Such variety in QoS is considered as
an important criterion for Web service
selection. Taher, L. et al (2005a) proposed a
generic QoS Information and Computation
(QoS_IC) framework for QoS-based service
selection in which the QoS selection
mechanism utilizes an established Registry
Ontology: which is used to present the
semantics of the proposed framework and its
QoS
structure.
The
QoS
selection
mechanism also uses the Euclidian distance
measure to evaluate the similarity between
the consumer/provider QoS specification in
the matchmaking process. We try to extend
the work of Taher et al (2005a) to
accommodate a user defined weighting
scheme. This weighting scheme is defined in
such a way that the highest weight signifies
the most desired QoS property. It decreases
base on order of priority. Also, the
weighting scheme normally between [0,1].
The algorithm presented here is a slight
modification of Taher’s as it take into
consideration the weighting scheme. As part
of the aim of this paper, we show that the
introduction of a weighting scheme into the
discovery algorithm can greatly address the
issues of “trade off” that can arise in service
selection. That is, depending on the weight
specification, certain web services can
perform better and hence be returned. The
examples in this paper helped us in making
these assertions. The sections in this paper
are organized as follows: Related work is
given next, it is closely followed by QoS
matching in Tahers work, then our propose
extension. Detailed examples are given next
to proof our assertions. Finally, conclusion
and future wo
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