A system design interview question: How to handle the data

I saw this system design interview question online. I would love it if anyone can analyze the question. Team X notify you that all indexes are ready then you can read them from their database. They are ready each day so they notify you each day that "ALL" indexes are ready, you can start delivering them. Clients show interest in your system into a specified index chosen by them and moreover a set of specified attributes for each index. The client also specifies a format to receive the file on such as XML, CSV, and so on and a preferred way such as email or FTP indexes ~ 20000 clients ~ order of thousands attributes ~ 5000 for each index.

I'd appreciate your ideas.