I was looking at the various APIs the project sources for data and was wondering does Bloomberg aggregate data sources from other vendors or does Bloomberg produce it's own market data for their terminals?
Most of the data on Bloomberg or any other market data terminal is going to from another data source. Either from an exchange, ratings agency, SEC reports, price reporting agencies, etc. They’ll also have proprietary data that are exclusive to their platform.
Not or, both. There is a crapton of data available in the terminals.