I am just wondering if open data have any limitations I may be missing. Can I for example get data through the Quandl API, do some calculations using the data, and resell the data? Is this legal?
Note: I am talking about free "open data", I understand premium open data does have terms attached to it.
The key question to ask whenever using data from an API or other source is "what licence is attached to the data?" Quandl doesn't give any definitive answer, but it points to the original dataset's licensing. In the T&C it reads
Quandl is an index. It is a conduit to data published on various locations on the internet. Like any search engine, Quandl makes no claim to own the data it indexes or caches. Quandl endeavours to respect copyright. If you believe this site is indexing your copyright data and you would rather it not do so, you may submit a take-down request.
and also:
Using the Website does not give you ownership or license of any intellectual property rights in the Website or in any content, information or data accessed on or through the Website, including content, information and data obtained from a third-party website.
Both are quite clear in not granting any explicit right to data re-use.
Quandl doesn't produced their own data and in their words "We respect data as IP. We believe that data publishers have the right to control the data they create." You're going to need to check limitations for the individual dataset you plan on using but in most cases I would guess the you're in the clear if you're using the open data to create a new product or one with additional value.
