Hi Guys.
Please can anyone share the documentation as to what are the different use cases of different options to fetch data from SAP DS e.g using Open Hub or Using Tables etc.
Regards.
Shaz
Shazin 
(BOB member since 2011-07-19)
Open Hub is a BW component and could be used to source data from BW but not directly from Business Suite systems such as ECC, S/4, CRM and SRM/APO.
For sourcing data from ECC 6.0, you can use RFC Streaming for simple table downloads (but no joins or complex logic on the SAP-end).
You can also use ABAP Data Flows using RFC Streaming and/or file-based transfer (I typically recommend RFC Streaming here) in which Data Services generates ABAP programs that can contain joins and SAP function calls to pre-filter the data for extraction. However, this is a more involved process and will also require you to create the ABAP Data Flows in your ECC development environment and have them transported through to QA and PROD.
For other scenario’s you may need to make BAPI function calls to get the data you require.
For near-real-time processing, you can receive IDocs as well but these can be more complex to work with due to their nested structures, much like XML.
Note that extracting directly from the database is typically frowned upon. The database itself is very complex, can change with any ECC Service Pack or Enhancement Pack and certain types of data is stored in a binary format which you cannot access directly at the database level (e.g. HR data).
Best practice is always to interface with any SAP environment through the Application Server and the proper APIs.
For data loading, direct database writes are a complete no-no. Again, you have multiple interfaces available such as generating IDocs or using BAPI function calls. Alternatively, you can generate upload files and load the data manually through LSMW although SAP recommends the use of Data Services for SAP S/4 data migrations/uploads as some of the legacy LSMW structures have not been maintained for the structure changes in S/4 (e.g. the removal of customer and vendor masters in favour of the business partner structures).
I strongly suggest going to the SAP Help site for Data Services and download the complete Technical Manuals (which is a bundle of all reference documentation) or download the Supplement for SAP individually if you only need details on how to interface with SAP ERP environments.
ErikR 
(BOB member since 2007-01-10)