Integrating Legacy Apps To The Web

Internet technologies have provided us with

universal connectivity, proven and cost-effective middleware, hardware independence and

shareability of applications. All these resulted in the Web becoming the de facto backbone

environment for distributed computing applications in an enterprise and the browser

becoming the universal end-user interface. While new applications can be developed for the

web environments, there is still the problem of the current applications. These have to be

migrated to the web environment.

Legacy application migration to web

environments is the third largest area of investments planned by enterprises after Y2K

compliance and ERP implementation in the next few years. There are a number of ways of

migrating legacy applications to Web-based environments. The process is also called legacy

web integration or web enablement of legacy applications.

Before examining the various methodologies

for integrating legacy applications to the web, let us examine the various applications

scenarios on the Web.

A simple web application model is used for

retrieving static information, which is already created and kept on the web server. The

information can be retrieved from a browser (client) through a request. In the interactive

web model, the user can input some additional data through the browser and thus create

dynamic content. Both the client and the server would have access to a database wherein

data gets accessed dynamically. The distributed web and the enterprise web models are used

for developing two-tier/three-tier client server distributed applications. In these

models, in addition to web client and web server, there will be an application server and

a database server. Programs and data are shared across the web client and the web server.

The browser would have the capability of executing `applets' written in Java.

Integration of legacy application into Web

can be achieved in various degrees depending upon end-user requirements. The simplest is

to provide a web interface for the legacy application. The end-user would be able to

access the legacy application through the browser. Alternatively, legacy data alone can be

made accessible by the Web. That is, a newly developed web application can have access to

legacy databases. In a third scenario, there could be two-way communication between the

newly developed web application and the legacy application for exchanging programs (code)

and data.

The integration described above is achieved

through a technique called 'wrappering'. In this technique, the legacy code and data is

encapsulated using a wrapper and deployed on to the Web. These wrapped contents can be

accessed using standard APIs and other middleware, available for web environments.

There are various types of wrappers for

various operations. These are application wrappers (wraps both code and data) services

wrappers (wraps system-level services e.g. transaction services, file system services) and

database wrappers (wraps only data). Examples of such wrappers are: 3270 terminal steam

wrapper, Java-CICS gateway or DB2 gateway etc.

Some examples of the applications using

wrapping techniques are given below:

Wrappering techniques use object-oriented

technology because of their encapsulation and abstraction features. Wrappers thus specify

a set of OO APIs (Object-Oriented Application Programming Interfaces) using which

application code or data can be wrapped. Wrappers can also be developed using procedural

APIs.

A number of commercial products are

available for various vendors which enable legacy application integration to the Web for

the above possible usage scenarios.