There exists many application that share common features, e.g. e-commerce application, bulletin board, news etc.
A common practice is; we just write/rewrite the logical tier and place the codes within the same server for all the application having common features.

Application shares a common feature but in general they are implemented separately. More precisely, codes for each and every application are placed in their respective server.
During this process, the class/method that may or may not be needed to particular application is also used and shipped which is obviously an overhead.

Solution

Design a common framework for application sharing common features which obviously includes reuse of classes.
Server then will issue an activation key or license key for that particular application.

Another problem is in updating, (i.e. if we want to add new feature or update existing features then we have to add/update in each and every application). Again if the bug is found in later part then we have to rectify for each and every application individually.

Here database consists of lists of tables that are used in application.

• Communication between central system and application can be achieved via SOAP.
• If a bug exits then we can rectify in a central system (NO NEED TO LOOK INDIVIDUALLY)
• If we want to add new feature or update/delete features then we perform in central system.
• Application communicates to central server via middle tier.
• Middle tier only knows the lists of classes and its methods available and with its uses.

For example

Central server has classes A, B and C.
A, B and C has a list of methods and they are used for certain purpose.

Middle tier has knowledge of messages it has to transfer and it is receiving messages from central server.
But contemporarily, middle tier is unaware of implementation.

Database Schema Snippets (XML can also be used in place of database)

1. Classes (classid, classsname)
2. Methods (classid, methods)
3. Application (applicationid, applicationname, licensekey, validityperiod, startdate)
4. Uses (applicationid, classid, methods)

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