You want to use the Web to let internal users or your customers look at corporate information. But you want to keep installation at the user end simple, and you don't want just anyone to get into your databases. That may be where an application server enters the picture .These software packages ,typically written in the Java programming language for use on Windows NT based systems ,act as go-betweens linking browser equipped end users to the databases that hold the information they need to access.
Application servers manage the process of connecting users to that data.
They set up an application session for each user, check identifications, fetch requested information from the appropriate database and build the data in to a Web page to serve directly to the users. What that means is that little or no application code needs to be installed at each end user's PC ,making it possible to develop thin client applications-server based software that runs in a Web browser and requires minimal support. Application server software packages, which by some counts are being sold by more than 40 vendors, also provide application management services such as monitoring system performance to sniff out bottlenecks. And they can be tied together to build large-scale applications that require multiple servers to meet the demands of users for data. Companies looking to more complex applications can hook application severs to separate software servers that process orders and other transactions and that distribute reusable chunks of application code called objects to users.