according to war file

1.web.xml

2.ibm-web-bnd.xml

3.ibm-web-ext.xml

This file is web.xml

This is an xml file. It tells to the server about the application.

Each web appication contain one deployment descriptor

Deployment descriptors are used for the describing the application environment and is used for what are the options we are used in an j2ee application

Deployment Descriptors is a Configuration File ( In XML).

This specifies the configuration for a EJB/Web Contaniner.

It is a sort of file that will be referred by the container when a specific request in made to the container.

The specifications made by Deployment Descriptor are;

1. Database Connections to be made

2. Location of EJBs

3. How to implement security &

4. Other important settings.

Portlets are packaged as WAR files with a Web application deployment descriptor (web.xml). This descriptor defines each portlet as a servlet within the Web application including unique identifiers for each portlet the portlet class and initialization parameters.

web.xml

The web.xml defines the Web application being deployed. This section will detail the required elements of the web.xml when deploying a portlet application.

For example you devlope one session bean and entity bean. you know that is entity bean and session bean but your application does not about your bean functionality.Because throw deployment descriptor you tell to application server about your bean functionality.