The Oracle EBS architecture is a framework for multi-tiered distributed computing. In the Oracle EBS model, services are distributed among multiple levels or tiers. A service is a process or a group of processes that exercise some business logic and provide a particular functionality. A tier is a grouping of services that can potentially span physical machines. In other words, a tier is a logical grouping of services that is not limited by physical nodes or machines. For Oracle EBS Online Training go here