Application Requester (AR). The AR accepts SQL requests from an application and sends them to the appropriate application servers for processing. Using this function, application programs can access remote data.
Application Server (AS). The AS receives requests from application requesters and processes them. The AS acts upon the portions that can be processed and forwards the remainder to database servers for subsequent processing. The AR and the AS communicate through a protocol called the Application Support Protocol which handles data representation conversion.
Database Server (DS). The DS receives requests from AS or other DS servers. The DS supports distributed requests and will forward parts of the request to collaborating DS in order to fulfill the request. The AS and the DS among themselves communicate through a protocol called the Database Support Protocol.