This graphic shows a complex multi-tier application. The tiers are the Internet; a middle tier composed of Web Cache, a Web server, a servlet engine, and iCache; and a database server. The Internet communicates with a the Web Cache server, which communicates with multiple web servers. Each server communicates with a Servlet Engine containing a Java Object Cache instance. The Java Object Cache reads from the iCache, which reads from the Oracle database, and from the Oracle database itself. One Java Object Cache also reads from an external data source.