The following diagram shows the technical schema of data conversion in SAP JCo (standalone version). Starting from a Java application, a Java method is forwarded via the JCo Java API (Application Programming Interface) and an additional Middleware Interface to RFC Middleware, where it is converted to an RFC (ABAP) call using the JNI(Java Native Interface) layer and RFC Library, and sent to the SAP system. Using the same method in the other direction, an RFC Call is converted to Java and forwarded to the Java application: