We are in the process of developing a portal for stock markets.

  My question is how to  get live data from a stock exchange like Nasdaq,CAC,DAX,Shanghai Composite,BSE etc. I know we need to use API to connect to particular Stock Exchange and get the data.

Can some one please let me know the technical process behind this scenario and which API we need to use for the same?

 Regrets if Iam asking wrong question at wrong place

Thanks in Advance