In simple terms, open data refers to data that anyone can freely access, reuse, and redistribute. However, in reality, open data is subject to certain restrictions, particularly when affected by intellectual property rights . Nevertheless, the term open data “can only be given to data that has an open license” . To make sure open data can be reused properly, open data licenses have been created.
Types of open data licenses
Open data licenses regulate the legal conditions for the use, distribution, and modification of datasets. According to Alamoundi et al. , these licenses can be grouped in 3 categories according to the level of restriction they impose on data use:
- Public domain: These licenses remove all rights. Anyone can use the data without asking or giving credit.
- Attribution: People can use the data, but they must say who made it.
- Share-alike: People must give credit and also share their new work with the same license.
However, we will see that there are also licenses that apply other types of restrictions. For example:
- Some licenses do not allow commercial use. This means that data can be used and even modified, but not for any commercial or profit-making purpose.
- Some licenses do not allow derivative works. In these cases, people can use the data but they cannot change it or create new works from it.
Most commonly used data licenses
Creative Commons Licenses (CC)
Creative Commons licenses are used a lot, not only for data. They help creators share their work with different levels of permissions. Here are all the main CC licenses:
- CC0 (Public Domain): Puts the data in the public domain. No credit needed.
- CC BY (Attribution): People can use, change, and share the data, but they must give credit.
- CC BY-SA (Attribution + Share-alike): Like CC BY, but new works must use the same license.
- CC BY-ND (Attribution + No derivatives): Allows reuse with credit, but the data cannot be changed.
- CC BY-NC (Attribution + Noncommercial): People can use and change the data with credit, but not for commercial purposes.
- CC BY-NC-SA (Attribution + Noncommercial + Share-alike): Like CC BY-NC, but new works must use the same license.
- CC BY-NC-ND (Attribution + Noncommercial + No derivatives): Most restrictive. Only allows reuse with credit, no changes, and not for commercial use .
Figure 1: Taken from Creative Commons license Wikipage in Wikipedia licensed under the Creative Commons Attribution-ShareAlike License 4.0 / cropped. Consultation date: 19/05/2025
Open Data Commons (ODC)
These licenses are provided by the Open Knowledge Foundation. They are split into 3 categories:
- PDDL (Public Domain): Works like CC0. It gives up all rights and places the data in the public domain.
- ODC-BY (Attribution): Similar to CC BY. It allows reuse, but users must give credit.
- ODC-ODbL (Open Database License): Requires attribution like ODC-BY or CC BY, and also demands that any new works made with the data use the same license .
Other data licenses that you can find
Besides the two licenses mentioned earlier, there are several other licenses that can be used. For example, some governments have their own Governmental Open Data Licenses. One great example is the UK government, which published some datasets on its portal under its own conditions. In Figure 2 you can see an example:
Figure 2: Taken from WiFi spots dataset in data.gov.uk licensed under the Open Government Licence. / cropped. Consultation date: 19/05/2025
In this case, the Open Government License of the UK, established by The National Archives , allows users to:
- Copy, publish, distribute, adapt and transmit the information.
- Exploit the information commercially and non-commercially, for example, by combining it with other information or by including it in their own product or application.
However, it is necessary to acknowledge the source by including the specified attribution statement or linking to this licence.
Also, the Linux Foundations has its own data licenses, which works in a similar way to the ones related to software. And, in some cases, there exist custom-made licenses created by the publishers to cover a particular specification. Anyway, to reuse content under these custom licenses, you simply need to check the permissions they grant.
So… which data license should you choose to open your work?
If you’re looking to share your own work, the easiest option is to choose one of the two we mentioned earlier: a Creative Commons license or an Open Data Commons license. Here are some basic guidelines to help you decide:
- Want to let anyone use your data without restrictions? Use a public domain license like CC0 or PDDL.
- Want to receive credit for your work? Choose an attribution license like CC BY or ODC-BY.
- Want derivative works to also remain open? Consider a share-alike license, such as CC BY-SA or ODC-ODbL.
- Don’t want your data used commercially? Use a license with a NonCommercial clause, like CC BY-NC or CC BY-NC-SA.
- Don’t want others to modify your data? Choose a license with a NoDerivatives clause, like CC BY-ND.
If you’re unsure, tools like the Creative Commons License Chooser can guide you step by step to find the best fit based on your needs.