Why there is a seperation between configuring and Mapping a servlet in the web.xml file?

[rajesh uppiliappan]

Why we configure and Map servlets separately using the <servlet> and <servlet-mapping> tags.
for eg.

<web-app>
  <servlet>
    <servlet-name>controlServlet</servlet-name>
    <servlet-class>com.jenkov.butterfly.ControlServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>controlServlet</servlet-name>
    <url-pattern>*.html</url-pattern>
  </servlet-mapping>
</web-app>    

instead we can do like

<web-app>
  <servlet>
     <servlet-class>com.jenkov.butterfly.ControlServlet</servlet-class>
     <url-pattern>*.html</url-pattern>
  </servlet>
<web-app>

what is the reason behind this seperation?

[Bear Bibeault]

There can be more than one mapping for any servlet.

[Stefan Evans]

Separation of concerns.
DRY (don't repeat yourself)

probably a few other programming guidelines could be applied, but those are the main two.

There are two distinct concepts here.
1 - "Servlet" defines a module that can handle a request, and gives a response
2 - "Servlet-mapping" tells the container "which servlet should I invoke when the user calls this URL"