What is a middleware and what is the functionality of Webserver?

A middleware in a 3-tier architecture sits in the middle of a client's machine and a database server. A middleware is where all the business related logic resides and it is also known as Web Application Server. (e.g. WebLogic from BEA, WebSphere from IBM, Oracle 9iAS from Oracle etc.)In distributed programming divide and rule is the name of the game and in this paradigm a middleware has a good share of responsibilities viz. load balancing, database connection pooling, security, transaction management related services, web and enterprise component deployment services, content management related services etc.