Licensing

Choosing a licence is one of the most important steps in open-sourcing a project. It is a choice you make initially that affects the project life-cycle and adoption outside of CERTH.

The Purpose of a Licence

Open-sourcing a project reverses the default “all rights reserved” model of copyright. A licence formally communicates the rights that you, as a copyright holder, grant to others for the use of your work. Without a licence, others have no legal right to use, copy, modify, or distribute your code, even if it is publicly visible on a repository hosting platform.

Licence selection significantly influences a project’s lifecycle and its external adoption.

Software licensing

The procedure for choosing a licence for CERTH-developed software is defined in the licensing recommendations section. In general, there are many good open-source licences and the choice of licence will depend on what you want to achieve. The three main classes of licence are:

• Permissive licences;
• Weakly-reciprocal licences;
• Strongly-reciprocal licences.

Permissive licences

Examples: Apache-2.0, BSD-3-Clause, MIT.

If you license your code under this type of licence, then anybody can take it, change it or combine with it as they wish and distribute the result also as they wish. They just have to respect basic conditions, such as including your copyright notice in the software they distribute. Among the freedoms you grant when you use a permissive licence is the freedom to modify your software and not distribute it as open source, i.e. to make it proprietary.

This is a good licence family if you want to allow others (e.g. a company) to use (or even modify) your software in a proprietary product, without releasing any sources.

Weakly-reciprocal licences

Examples: LGPL-3.0, LGPL-2.1, MPL-2.0.

If you license your project under this type of licence and somebody takes your code and combines it with theirs, upon distribution they do not have to disclose their own sources, just yours, whether or not they have modified them, and under the same licence you used.

This is a good licence family if you want to benefit from improvements to your code but do not want to force the users of your code to disclose their own sources.

Strongly-reciprocal licences

Examples: GPL-3.0 and GPL-2.0.

If you license your project under this type of licence and somebody uses your code and combines it with theirs, they will need to release the sources of both your code (modified or not) and their code.

The vision of the creators of the GPL was to generate an ever-growing body of free software by forcing/inviting users of your code to release theirs as well.