ALSTOM interview questions

1. What is synchronous and asynchronous in sap? In case of synchronous which one is better odata or RFC? 2. What's better Odata, RFC or webservice? 3. What's difference between ALE and EDI? 4. How to update fields at VBAP and VBAK from a custom segment at IDOC? 5. There is one BAPI for purchase order create and there are 2; different programs. In one program BAPI us called with call function and in another program BAPI is called with destination none then what will happen? What will be different? 6. Export to memory is called and then update function module is called and inside update function import to memory is called then will that import statement work? 7. What is sap memory? 8. What's difference between ABAP cds and hana cds? Which one is better or higher performance? 9. Can we call hana cds directly at ABAP report?