Hi Shalini,
The document which you are referring is pulling data from a table which get loaded by a flat file directly from users in ECC (or) R/3 to BW system. and when users execute the tcode: se93, after they choose the CSV file, the ABAP program runs in backed which loads the data in table and then raises an event to trigger the process chain in BW automatically.
As mentioned by Phani, this doesn't support delta loads, but in the document, it is being loaded to a custom master data (ZMAT_PLANT), where data can be overwritten.
And if you have similar scenario but you need to load the transaction data, then you can load the delta's by choosing the delta pointer from the generic data source ( you can search about generic data source delta concepts from SCN).
Lastly, if you requirement is load data from flat file which is present in BW application server, then you can simply schedule the process chain by choosing the path from AL11 directory in info package and then run the DTP.
so the design/modelling get changes according to requirement.