Figure showing five possible tiers in a model J2EE application: a browser tier containing HTML documents or applets, a client tier containing Java clients, a web services tier (a web server and servlet container) containing servlets and JSPs, an EJB tier (an application server and EJB container) containing enterprise beans, and, finally, a database or other data source. The browser tier and the client tier talk to the web services tier. The web services tier and the client tier talk to the EJB tier. The enterprise beans in the EJB tier interact with the data source.