Licences are essential to enable data reuse. You need a licence to clearly state what others can do with your work, whether they must cite it, and how they can share derivative work.

Bespoke and standard licences

The two main types of licence [1] are bespoke and standard licences. We suggest you avoid bespoke licences, as they are difficult to create, although we recognise you might need them in some cases. Standard licences are usually available when depositing the data in a repository – often you will be asked to pick an option among:

• Creative Commons
• Open Data Commons
• Open/Non-Commercial Government Licences
• Public domain.

Each of these has sub-options, which might be confusing if you have never heard of them. We recommend that you stick to public domain licences as far as possible. These allow the greatest reusability and place no restrictions upon the way you use data. If you are concerned about attribution, it is possible to add an optional suggestion that re-users state the origin of data.

Getting help to choose a licence

The licence selector tool [2] can help you address doubts and make an informed decision. Note that this tool also addresses software, although GitHub [3] discusses the topic in more detail. Guidance [1] from the Digital Curation Centre in document format might also be helpful.

The three layers of licences

When depositing data, you should consider three layers [4] of licences:

• The legal code (i.e. the law): this is the “traditional” version of a licence, written with legal jargon and used in courts of law.
• A human-readable licence: this is a version of the legal terms that laymen will understand. As a researcher, a human-readable licence will clarify what can and cannot be done with the data.
• A machine-readable licence: this is the least common version of licence but a very important one. A machine-readable licence tells computers what the key freedoms and obligations are with respect to the data. Automated software, search engines and customised algorithms all benefit from machine-readable licences.

When applying a licence to your data, these three layers should be in place. In some cases, it is more practical to focus on one of them and then address the others at a later stage. If possible, we recommend you avoid this, but it is certainly more desirable to have at least one of these layers in place rather than none at all.

Note that Creative Commons licences [4] always consider all three layers above.