Ownership of user-contributed data

To: SofaCinema (DVD rental service)
From: Me

Is it possible to export the movie ratings that I've added to your system?

Response: Unfortunately it is not possible to export your rating data.

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To: last.fm (social music site)
From: mlorenzi

For my research thesis in computer science about small-world-networks and music similarity i would like to use last.fm data. But that would require to get an amount of data about the users and their top50 tracks (as it is accessible from the webservice). Is it possible to get a database-dump...?

Response: Unfortunately not. We used to provide such a service but we're unable to do so any more ... we can't release more recent data, and that's a shame. ... It is considered too valuable.

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:-(

However, there is hope in that last thread that it will be possible to export all your own data at some point.