A Model for Web Services Discovery with QoS

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3 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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A Model for Web Services Discovery with QoS

Paper by Shuping Ran

Critique Report by Eyhab Al
-
Masri

(Discussant)

and Razieh Niazi

(Presenter)


Brief summary

In the paper

titled

“A Model for Web Services Discovery with QoS” written by Shuping Ran, the
autho
r proposes a solution to enhance the discovery of Web services using Quality of Service (QoS)
attributes. In recent years, QoS support for Web services has become a widely researched area and has
shown to be an effective mechanism in Web services’ discover
y particularly in differentiating between
services that share similar functionalities. In the proposed solution, Ran recommends a new discovery
model for Web services with the addition of QoS Certifier which is responsible for verifying QoS claims
supplied

by service providers and issuing Certification IDs for services whose QoS claims can be verified.

In order to incorporate QoS Certifier into the
existing Web service

discovery model, Ran
introduces a slight modification to the current Web services’ archi
tecture such that registration is performed
at the UDDI only after a service provider verifies QoS claims with the Certifier. Under this new model, a
service provider prepares a set of QoS measurements and communicates this information to the Certifier
whi
ch then begins checking QoS claims and sends back a notification to the service provider. This
notification is either an acknowledgement that the QoS claims have failed, or a Certification ID that the
QoS claims have been successfully verified. Once the se
rvice provider is issued a Certification ID, it begins
the registration process through the UDDI registry, providing both functional and non
-
functional
information (QoS claims), along with the Certification ID. The UDDI performs a verification process for
the Certification ID and communicates with QoS Certifier to check whether
it

is valid or invalid. Once
UDDI verifies this information, it registers the service provider’s information.


Points in favor

The framework proposed by Ran offers an enhanced Web
services’ discovery model in the sense
that it provides a mechanism for service providers to associate and include QoS metrics within the UDDI
registry. In addition to that, verifying QoS information is applied by QoS Certifier which gives assurances
to cl
ients that supplied QoS are valid and can be trusted. Furthermore, the solution allows clients to
articulate their search queries based on QoS attributes. The paper also suggests at least twenty QoS
properties that can
be
measured and associated with Web s
ervices.


Points Against

Although Ran’s solution has the potential of providing QoS support for Web services’ discovery,
there are technical challenges and limitations associated with the proposed
system
. One of these limitations
is the redundancy of per
forming QoS measurements. QoS measurements have to be supplied by the service
provider at the time of registration while QoS Certifier will eventually perform another round of QoS
measurements to verify the service provider’s claims, and therefore, QoS mea
surements are conducted at
least twice. In addition to that, Ran’s solution proposes a major change to the existing UDDI specification
(Version 3), which may be very problematical at this stage due to the fact that many software vendors have
already endors
ed the UDDI standard with its latest specification and have incorporated UDDI support
within their software products such as Enterprise Windows Server 2003, WebSphere, and among others.

Ran’s paper did not provide a clear explanation on key issues such as

the storage of QoS
information within
qualityInformation

tModel, how data types will be managed or declared, and the
possibility of linking QoS information to bindingTemplates. The ability to incorporate or relating QoS to
bindingTemplates is very useful
in the sense that they can be used for multiple offerings of the same Web
service. For instance, a service provider that has variations of the same Web service (i.e. Enterprise,
Professional, and Basic) will eventually have different QoS measurements for e
ach of these offerings, and
therefore, applying the same QoS information to all bindingTemplates may not be accurate or helpful.

In addition to that, Ran’s solution lacks implementation details or experimental results. The system
proposed only provides an

idea of what can be done, however, no design, implementation, or performance
testing could be found anywhere in the paper. The author only provides one example of a SOAP
request/response for illustration purposes, and does not provide any details on how t
he system can be
implemented or designed. Potentially, the author could have implemented a working model for the twenty
Web service attributes and how they can be used within the UDDI through existing tModels structure.
However, the lack of implementation
details and experimental results makes the task of verifying the
feasibility of this solution very difficult.

Furthermore, having QoS information at the time of registration will impose a restriction on service
providers in the sense that they have to con
tinually provide QoS claims with every Web service that needs
to be published

as the author suggests
, “In the proposed model, a Web service provider needs to supply
information about the company …. as well as to supply quality of service information…” (Sec
tion 2.2).
The fact that every time a service provider has to provide QoS claims at the time of registration may not be
potentially suitable due to the fact that service providers have to devote more time, money, and extra effort
to perform QoS measurement
s on their Web services (i.e. use built
-
in or third party QoS measurement
tools). In addition, requiring service providers to supply QoS information at the time of registration may
allow them to think of ways on how to improve QoS measurements.

Another ma
jor limitation found in Ran’s paper is periodic updates of QoS information. Due to the
nature of how Web services operate, and how they strictly depend on network traffic, it becomes critical to
perform periodic updates to QoS measurements to ensure that t
he claims are constantly valid.

Many of the QoS metrics are performed over a period of time (i.e. days, weeks, months) which
makes the task of conducting QoS measurements
very
time consuming. However, from Ran’s paper, it
conveys that QoS measurements are

semi
-
instant or simple to generate which is not entirely true. In
addition to that, in Ran’s solution the UDDI is required to perform additional tasks such as verifying
Certification IDs at the time of registration

as the author suggests
, “UDDI communicat
es with the certifier
to check the existence of the certification…” (Section 2.2). Performing this task will likely increase the
overhead and work
executed

by the UDDI which may not be practical since UDDI is intended to serve as a
service directory and do
es not have the capability to serve as a communication link. Furthermore, the
UDDI does not have the built
-
in functionality to communicate with third parties, and the paper does not
clearly define how this task can be performed or developed.


Comments for

Improvement & Conclusion

Although Ran’s solution provides a way to include QoS information at the UDDI registry, there is
room for improvement. The supply of QoS information should be made optional and service providers
should not be enforced to provide
them at anytime. In fact, supplying this information by service providers
will necessitate the verification of their QoS claims (i.e. Certifier)
;

however, it would be desirable if there is
a service broker that can collect QoS information about Web service
s in a transparent manner based on
entries within the UDDI registries. This will not force service providers to devote efforts on providing QoS
measurements at the time of registration and prevents any room for manipulation. In addition, having a
service b
roker for measuring QoS information for Web services does not require any modifications to be
made to existing standards (i.e. UDDI) and enables the monitoring of Web services across stages (i.e.
traffic analysis, reputation, and among many others).

Ran’s

solution provides a mechanism for improving the discovery of Web services based on QoS
attributes, however, it lacks implementation results, and requires major changes to the existing UDDI
standard. In order to improve this system, it is important to cons
ider the fact
that

QoS measurements should
be conducted in a fair and transparent manner, clients should be able to customize the discovery process
using a combination of QoS parameters as constraints, and support of periodic QoS updates is unavoidable.


Reference:

Ran, S., “A Model for Web Services Discovery with QoS”, ACM SIGecom Exchanges 4(1): pp. 1
-
10, 2003