A Model for Web Services Discovery with QoS

SHUPING RAN

CIS 6650.01

Eyhab Al-Masri, & Razieh Niazi

Paper Reading, Critiquing, and Presenting

Need for QoS-based Discovery of WS

Web service textual information is very

limited

Not easy to distinguish

Web services from each

other

Using keyword-based

discovery technique is not efficient

No Support for QoS within Registries

Unfortunately, current UDDI and ebXML implementations do not provide ways to incorporate QoS information

Service Providers advertise their own QoS claims

or Clients perform their own QoS

measurements

Suggested Solution: Pros

Ran suggests a QoS Certifier authority that can confirm SP’s QoS claims by issuing a Certification ID

AdvantagesSystem provides a way to:• offers QoS support for Web services,• verify QoS claims,• enable clients to search for WS using QoS

attributes

Suggested Solution: Cons

Disadvantages

Repetitive• SP performs QoS measurements• Certifier performs QoS measurements

Extends the current UDDI standard to endorse this solution

• Problematic: Many UDDI implementations are already existing

• Does not thoroughly take advantage of UDDI data structure

Suggested Solution: Cons continued…

Implementation Clarity Not Clear• How QoS information is stored within

qualityInformation tModel– Unknown

• How data types are managed or declared– Unknown

• How qualityInformation tModel is connected to the bindingTemplate

– No explanation given

No actual implementation of the system• Only examples given for illustration

purposes• Could not verify if it can be applied

Suggested Solution: Cons continued…

SP must supply QoS information• Imposes a restriction that every WS has

to have QoS information– “In the propose model, a Web service provider

needs to supply information about the company … as well as to supply quality of service information….” Section 2.2

» May not be possible» Allow SPs to think of ways on how to

improve QoS measurements

Periodic updates• Solution does not discuss or give details as

to how frequent QoS information is updated

Suggested Solution: Cons continued…

QoS measurements are not instant• Solution implies that QoS certification

is quick and easy:1. the Web service provider first needs to

communicate its QoS claims to the service QoS certifier

2. The certifier checks the claims and either certifies or down grade the claim

3. The outcome is sent back to the provider with certification identification information

• QoS measurements take time Additional UDDI work

• “UDDI communicates with the certifier to check the existence of the certification…”– Extra work on UDDI

Get data

QoS...

Suggested Solution: Cons continued…

How QoS measurements are conducted?

Using existing tools… Transparent and fair?

Suggested Solution: Cons continued…

Who is really the QoS Certifier?Who is really the QoS Certifier?

Third party?Third party? Supervised Supervised by UDDI?by UDDI?

Middleware?Middleware? ServiceServiceBroker?Broker?

Extending UDDI data structureCurrent UDDI Data Structure

BusinessEntity

BusinessService

bindingTemplate

publisherAssertion

tModels

Ran’s new UDDI Data Structure

businessEntity

businessService

bindingTemplate

publisherAssertion

qualityInformation

tModels

Interesting Issues:

Service Providers have to go through additional steps to get their Web services published• Registration at Certification authority• May have to pay fees to get QoS

certificate Section 2.1: “The new UDDI registry is

a repository of registered Web services with lookup facilities”• UDDI version 2 and 3 already have lookup

functionality, uncertain what the author really implies by new UDDI

• tModels already existed by the time paper was written

Possible Improvements

QoS support should be optional UDDI is not intended to be a search

engine, therefore a service broker may solve the problem

Service Provider

Service Broker

UDDI RegistryPublish

RetrieveInfo

Verify QoS Info / Issue URL

Web ServiceConsumer

1

2 3

4Request/Respons

e

5

Inv

oc

atio

n

Conclusion

Although Ran’s solution provides a way to enhance the discovery of Web services using QoS, • It lacks implementation results, • Requires major change to UDDI standard, and • Does not provide adequate level of details on

QoS measurements and Certification authority. QoS measurements must be performed in

a transparent manner Clients should be able to customize

discovery process using QoS parameters Periodic QoS updates and service lifecycle

are essential to both SPs and clients

Reference

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

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