Our team is planning to start our own Bitcoin Exchange where an end-user could Register, make transactions(Sell/Purchase bitcoin), keep their wallet and could see live Graph of all the listed crypto-currencies. And yes we do know what are all the legal, financial and technical requirements/challenges for this.
We researched about it a lot and found everytime that there are certain websites/Exchanges like blockchain.info that provide their own API for all such tasks.
However, if we want to create our own Exchange, we can't rely fully on any third party website. So, what my main question is that where do all these websites get their data from, whenever any transaction is made on their website, do they keep this record only to their selves(in their own DB) or is their any central entity of this whole blockchain web where this transaction needs to be registered also?
And where do these websites get data for their live graphs showing the current market value of all the currencies?
Any clarification of my query would be deeply appreciated.