Creative Commons (http://www.creativecommons.org/) offers a library of standardized licenses, some of which may be used with data. Creative Commons recommends the following three licenses for data sharing. We recommend the CC BY 4.0 license in most cases:
Creative Commons recommends use of the above licenses only. It does not recommend use of any NonCommercial (NC) or NoDerivatives (ND) licenses. For more information, see this article on the Creative Commons wiki.
In addition to Creative Commons, the Open Data Commons group (http://opendatacommons.org) has developed a number of legally binding tools to govern the use of databases and data. Using a combination of copyright and contractual standards, they have created three standard licenses. In addition, Open Data Commons has developed a suite of “community norms” that complement use of the formal licenses. While not carrying the force of law, these norms may be used to express your beliefs about appropriate data sharing and reuse.
The three ODC licenses are:
There is no single right answer as to which license to assign to a database or data content. Note, however, that anything other than a CC0 or ODC PDDL license may present challenges for subsequent users of your data. This is because of the problem of "attribution stacking." It may be possible to extract data from a dataset, use it in a research project, and still maintain information as to the source of that data. It is possible to create a dataset derived from hundreds of sources with each source requiring acknowledgement. Furthermore, the data in the other databases may not have originated with it, but instead have been sourced from other databases that also demand attribution. Rather than legally require that everyone provide attribution to the data, it might be enough to express the community norm that says “if you make extensive use of data from this dataset, please credit the authors.”