Adding externally sourced data to any business intelligence app can yield new insights. For example, looking at how the weather affects the sales of certain products could be hugely beneficial to retailers. Much data is freely available on the Web, but it is rarely in an easily consumable form. This is exactly the problem Qlik DataMarket solves, by providing curated, normalized datasets that can be easily loaded into Qlik Sense available in the cloud.
Note that Qlik DataMarket works as a source for Qlik Sense irrespective of whether you are running in the cloud or not.
