The first step in a BDC session is to identify the screens of the transaction that the program will process. Next step is to write a program to build the BDC table that will be used to submit the data to SAP. The final step is to submit the BDC table to the system in the batch mode or as a single transaction by the CALL TRANSACTION command.
The SAP front-end s/w can either run on the same computer or on different computers provided for that purpose. User terminal input is accepted by the SAP terminal program SAP GUI, converted to SAP proprietary format and sent to the SAP dispatcher. The dispatcher coordinates the information exchange between the SAP GUIs and the work processes. The dispatcher first places the processing request in request queues, which it then processes. The dispatcher dispatches the requests one after another, to the available work process. The actual processing takes place in the work process. When processing is complete, the result of a work process is returned via the dispatcher to the SAP GUI. The SAP GUI interprets the received data and generates the output screen for the user.
An instance is an administrative unit in which components of an R/3 systems providing one or more services are grouped together. The services offered by an instance are started and stopped at random. All components are parameterized using a joint instance profile. A central R/3 system consists of a single instance in which all-necessary SAP services are offered. Each instance uses separate buffer areas.
The R/3 basis system guarantees the integration of all application modules. The R/3 basis s/w provides the run time environment for the R/3 applications ensures optimal integration, defines a stable architectural frame for system enhancements, and contains the administration tools for the entire system.One of the main tasks of the basis system is to guarantee the portability of the complete system.