In order to integrate Drupal with SAP you need SAPRFC which is a extension module for PHP 4 and PHP 5. With SAPRFC is possible call ABAP function modules in SAP R/3 from Drupal or any PHP scripts. You can use the powerful PHP language to create a web applications or interface programs with a connectivity to the SAP R/3. You can also write RFC server program in PHP and call PHP functions from SAP R/3.
To be continued..