Suppose if a scenario is given where we have put the web server on top of application server in what ways this web server can help
1) on a non-distributed enterprise application(ear
2) on a distributed enterprise application(ear)
3) on a web application(war)...i think in this case we do not require a app server
In a multi-tier architecture, the app-server performs the business-rules and the data-access layers. This way different front-ends can be used against the one app-server, eg web, mobile, native.