Chapter 4

Legacy Systems Integration

(Integration between the L.S. and the Web)

Introduction

The organization investment in legacy system is worth considering .

It may have spent a great deal of money and human resources developing the system that are now in place in the organization .

Definition the legacy systems • Existing applications and systems within

your organization that are not Web-based or integrated with yet the Web are referred to as legacy system .

• legacy system and applications may reflect the way the organization operated in the past, deserving the name legacy systems .

Definition the legacy systems

• A legacy system is an existing computer system or application program which continues to be used because the user does not want to replace or redesign it .

• Legacy systems are considered to be potentially problematic by many software engineers for several reasons. Legacy systems often run on obsolete (and usually slow) hardware, and sometimes spare parts for such computers become increasingly difficult to obtain.

Evaluating Legacy Systems

• The organization has many applications and systems in place, some of them work smoothly, others in need of upgrade or overhaul, when you are adding the Web to your arsenal of tools, you have the opportunity to reevaluate existing systems and applications and determine which ones should are worth retaining, which ones need to be upgrade, and which ones should be replaced .

Evaluating Legacy SystemsHow you can determine which legacy systems

are worth retaining ? consider the systems (hardware and operating

system) that are in place and then survey the applications running on those systems . It may be worth retaining the systems and revamping or replacing the applications .

It is important to decide which systems and applications are basically performing their intended functions and are worth integrating into the Web and which level of integration is the most appropriate for each application .

The three basic levels of integration that may work with your legacy applications:-

• Frontend integration whereby a Web GUI (Graphical User Interface) fronted provides the presentation layer for the legacy application .

• Business logic integration whereby the business logic of the application is integrated with the web .

• Data access layer integration whereby the backend data access is integrated with the web .

Table 4.1 Inventory of legacy Applications for the A corporation

Application

Function PlatformRetain , Upgrade

, Replace ?Web Integration

Vacation Scheduler

Keep track of each employee’s vacation

MainframeRetain-works fine but needs better interface

Frontend integration

Payroll Processor

Payroll processing for salaried and hourly

employees as well as contractors

UNIX work station

Upgrade –need to allow for

customization of reports and

accessibility by others and need to tie

in with other accounting software

CORBA interface available , business services integration

Benefits

Employee options on healt , dental , vision ,

and life insurance , dependent care

accounting

PC

Replace – proprietary application

processing , manual updates

Replace with interactive self

service java application that works

on intranet , JDBC interface to backend

databases

Library

Obtain market research materials

from market research firms and from public

sources

UNIX serverRetain – New Web

application built for intranet

Already integrated with intranet

1) Fronted Integration

• Understand Integration Between A Web GUI fronted and A Legacy System Application.

• Determine Which Applications Should Be Integrated on the presentation layer

• Fronted integration provides the loosest form of coupling between a legacy application and the Web. The easiest way to integrate an application with the Web is to provide data entry facilities through a forms-based Web fronted .

Web-basedInterface

GUIEnd User

Legacy System

The limitations to Fronted Integration

• CGI (Common Gateway Interface) scripts increase network traffic since data is passed through to the legacy application directly .

• Increase in HTML via the browser

2) Business Services IntegrationThere are a number of technologies that can be used to

integrate your legacy application at this level

1- Integration With Remote Procedure Calls (RPCs).– RPC communication is limited to between client and server.– RPC is suitable for more fine grained jobs.– Programming will be much easier .

LegacySystem

End UserInternet

Update Program

2- Common object request broker architecture ( CORBA )

Common object request broker architecture ( CORBA )

• What is CORBA?What does it do? • CORBA is the acronym for Common Object

Request Broker Architecture, OMG's open, vendor-independent architecture and infrastructure that computer applications use to work together over networks. Using the standard protocol IIOP, a CORBA-based program from any vendor, on almost any computer, operating system, programming language, and network, can interoperate with a CORBA-based program from the same or another vendor, on almost any other computer, operating system, programming language, and network.

Common object request broker architecture ( CORBA )

• What is CORBA good for?• CORBA is useful in many situations. Because of the

easy way that CORBA integrates machines from so many vendors, with sizes ranging from mainframes through minis and desktops to hand-helds and embedded systems, it is the middleware of choice for large (and even not-so-large) enterprises. One of its most important, as well most frequent, uses is in servers that must handle large number of clients, at high hit rates, with high reliability. CORBA works behind the scenes in the computer rooms of many of the world's largest websites; ones that you probably use every day. Specializations for scalability and fault-tolerance support these systems. But it's not used just for large applications; specialized versions of CORBA run real-time systems, and small embedded systems.

 

Common object request broker architecture ( CORBA )

• How about a high-level technical overview?• CORBA applications are composed of objects, individual units

of running software that combine functionality and data, and that frequently (but not always) represent something in the real world. Typically, there are many instances of an object of a single type - for example, an e-commerce website would have many shopping cart object instances, all identical in functionality but differing in that each is assigned to a different customer, and contains data representing the merchandise that its particular customer has selected. For other types, there may be only one instance.

3) Data access layer integration

Legacy System

DB

Web-basedInterface

GUI

InternetEnd User

Common object request broker architecture ( CORBA )

• Who is using CORBA already?

• Thousands of sites rely on CORBA for enterprise, internet, and other computing. The Object Management Group maintains an entire website devoted to user design wins and success stories. At last count, there were over 300 stories on the site.

Backend Integration

• Java Language Support .• Java Database Connectivity ( JDBC ) .• JDBC Drivers

There are four different types of JDBC drivers :-– The JDBC – ODBC Bridge .– A native –API partly Java Technology – based driver .– A net –protocol All Java Technology – based driver .– A native protocol All Java Technology based driver .

Legacy Applications

• Appreciate the ease of use gained from the marriage of a web GUI frontend to a legacy application.

• Decide if some of your legacy applications just need a new frontend to be more usable .

• Examples:– Registration and Admission.– E-Commerce.

End The Chapter

Thank you for attention

& good listening