Managing Information Access to an Enterprise Information System Using J2EE and Services Oriented Architecture

180 Managing Information Access to an EIS Using J2EE and Services Oriented Architecture

proxy. External services are imported into the Gateway and made available

internally to the enterprise as proxy services . Likewise, internal services are

imported into the Gateway and made available as proxy services externally.

These services are also published to the relevant UDDI directories where

required.

7.5 Quality of service for Web services

Quality of service (QOS) refers to the capability of a platform to provide a better

service to a selected application.

It is a challenge to build systems that deliver extremely high levels of service

because many variables need to be considered. The success of an application

depends on scalability, performance, availability, security, and manageability,

among other things, and all these are critical considerations if you are to avoid

failure.

In terms of Web Services, QOS covers a range of techniques that match the

needs of service requestors with those of the service provider's that are based on

the network resources that are available.

This section describes some considerations about QOS in a Web service

context. It does not discuss the scalability and availability topics, because these

issues are inherent to the underlaying middleware platform that hosts the Web

services. For details of these topics as related to the WebSphere platform see

the references in 7.6, “Further information” on page 195.

7.5.1 Performance

Often non-functional requirements are overlooked. It can happen that a project

manager faces the performance issue only in a production environment when the

performance challenge should be considered from the design phase of the

project.

One of the major drawbacks of the Web services technology is the performance

issue. The great interoperability of Web services is often paid for in terms of the

increased time for processing the message. XML parsing is always a heavy job,

even as parsers are becoming smarter.

The service designer should consider that service granularity has a significant

impact on the response time of Web services and decide on the level of

granularity of the functions to be exposed as Web services to avoid unnecessary

message exchanges across the Internet.

Chapter 7. Using Web services 181

As a performance rule, the service designer should strive to publish coarse

grained services that accept all necessary parameters and information, thereby

allowing the service provider to accomplish as much as possible on behalf of the

consuming application. The goal is to minimize the number of requests that a

consumer makes in order to accomplish a set of business tasks. A minimum

number of requests ensures minimal effects due to network latency, system I/O,

and thread or process wait states that when aggregated with multiple requests

can result in significant delays.

For example, in case of a purchase order service, it is a good idea to allow the

consumer to specify product SKU numbers, quantities, credit or debit card

information, billing and shipping address information, and discount coupons all

within a single request. The request itself may initiate multiple atomic

transactions (credit card authorization, submission of charges, inventory query

and update, and order fulfillment) at the service provider that can each be

undone or reversed if needed while supporting the overall business process.

WebSphere Application Server V5.1 has introduced many enhancements on the

performance side for the Web services so that migration to the latest release can

improve performance with a factor that can vary from two to four. It has also

added a cache capability for Web services called the

WebSphere dynamic cache

service

. For those cases where it is applicable, Web services performance using

the dynamic cache is greatly augmented.

The cache mechanism needs a unique identifier to recognize which service

requests can be served by the same reply. The tools let the user specify this

identifier from Web services specific component, s including:

򐂰 SOAP Action

򐂰 SOAP Envelope

򐂰 Servlet path (in the JSR 109 case, this refers to a port-component)

򐂰 SOAP operation (requires parsing of the SOAP message)

򐂰 SOAP operation parameters (requires parsing of SOAP message)

An essential tool is Tivoli® Performance Monitor that is packaged with

WebSphere Application Server. This tool receives performance data from the

application server and plots performance graphics at run-time (see Figure 7-7 on

page 182).