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titleSoftware Licensing Guides Series

Table of Contents

Table of Contents

This page provides an overview of various tools and resources for selecting, checking and selecting managing open-source software licences and their compatibility.

Overall information and licence lists

Permissive and copyleft licences

Image Removed

(Based on materials from ORCRO)

Permissive licences have simple requirements – to credit original work, describe changes, provide a disclaimer, etc. Copyleft licences (“reciprocal”, “protective”, “restrictive”, derogatory: “viral”) require the rights to be preserved in derivative works. If you use any components (libraries) with copyleft, you are obliged to make derived source code available, which may include the entire product/project!

  • Permissive – do anything
    • MIT – short and simple
    • ISC (OpenBSD) – further shortened equivalent
    • BSD – some versions require including the disclaimer
    • Apache 2.0 – requires notice of changes, grants a license to patents unless litigating and mentions the preservation of trademark rights
  • Weak copyleft – file (library) scope
    • MPL 2.0 – simple, allows static linking and licence variants with additional terms
    • LGPL 2.1 – cleaned text of LGPL 2.0, allows dynamic linking without enforcing copyleft
    • LGPL 3.0 – grants the use of patents; the end-user must be able to install a modified version – it prohibits closed devices, DRM or hardware encryption or patents retaliation; compatible with Apache 2.0
  • Strong copyleft – project scope
    • GPL 2.0 – often used
    • GPL 3.0 – grants the use of patents, the end-user must be able to install modified software, compatible with Apache 2.0
    • AGPL 3.0 (Affero) – network protective: external use of modified(!) code requires its availability – network use is a distribution of the software, modified source code must be available
  • Proprietary – these licences restrict user rights and protect the commercial interests of copyright owners

Per-feature or tabular comparisons of licences and categorised lists

Licence compatibility

GPL licences compatibility

Arrows are transitive and go from licences of the components toward the licence of your project

A chart illustrating compatibility relationships between different free software licenses.  For details, see the FSF's license list page.Image Removed

(From https://www.gnu.org/licenses/quick-guide-gplv3.html)

Above, per the dotted line, “GPL 2 only” is not compatible with GPL 3”, but ”GPL 2 or later” is. A more detailed view with precisely stated licences:

Image Removed

(From David A. Wheeler 2007, https://web.archive.org/web/20210101030518/https://dwheeler.com/essays/floss-license-slide.html, SVG variant: https://en.wikipedia.org/wiki/License_compatibility#/media/File:Floss-license-slide-image.svg)

On AGPL compatibility:

  • (L)GPL 3.0(+) components can be used in software under AGPL, thanks to an explicit rule in GPL
  • Code under AGPL cannot be used in (L)GPL projects unless dual-licensed

Relationship between most used licences in GÉANT

Following is a graph of licences that are most frequently used in GÉANT projects that were scanned using the Mend tool. It is based on the two previous graphs.

Image Removed

Dual and multi-licensing

  • Dual and multi-licences can help avoid licence compatibility issues, making the use of components more flexible.
  • You can choose a licence compatible with the one used for your software. But you cannot dual-license your software to match some components with one licence and others with another. Licences of all used components must be compatible with all of your licences.
  • “Or later”(often expressed as “+”) licence variants imply the applicability of later, possibly still non-existing, versions of these licences. This is sometimes implied unless you explicitly decline it.
  • Some licences include automatic relicensing (MPL 2.0, EUPL 1.2, CeCILL), while EUPL comes with a full list of licences it can be combined with.

Licence compatibility matrices or checkers

Joinup Licensing Assistant – Compatibility Checker, https://joinup.ec.europa.eu/collection/eupl/solution/joinup-licensing-assistant/jla-compatibility-checker

Licence Compatibility Checker software

In-licences (licences of components) are in rows and out-licences are in columns:

Image Removed

(Source: https://github.com/HansHammel/license-compatibility-checker)

Open Source Automation Development Lab (OSADL) matrix and rules

In-licences are in columns and out-licences are in rows:

Image Removed

(Source:  Meeker, H., & von Wendorff, C. (2019). Fulfilling open source license obligations: Can checklists help?, https://events19.linuxfoundation.org/wp-content/uploads/2018/07/OSLS-2019-Fulfilling-Open-Source-license-obligations-Can-checklists-help.pdf)

More at

GNU GPL licences compatibility 

EUPL 1.2

Creative Commons licences

Risks of licences

Risk mitigation against potentially harmful legal threats or behaviours by free-software licences

...

Frequently used protective and permissive licenses

...

AGPLv3

...

GPLv3

...

GPLv2.1

...

LGPLv3

...

LGPLv2.1

...

MPL-2

...

BSD

...

SaaS/cloud

...

Yes

...

No

...

No

...

No

...

No

...

No

...

No

...

Tivoization

...

Yes

...

Yes

...

No

...

Yes

...

No

...

No

...

No

...

Patent trolling

...

Yes

...

Yes

...

No

...

Yes

...

No

...

No

...

No

...

Proprietization

...

Yes

...

Yes

...

Yes

...

Partial

...

Partial

...

Partial

...

No

...

Granularity/reach

...

Project

...

Project

...

Project

...

Library

...

Library

...

File

...

N/A

...

Trademark grant

...

Yes

...

Yes

...

?

...

Yes

...

?

...

No

...

No

(Source: https://en.wikipedia.org/wiki/Free-software_license)

Mend resources

Other software composition analysis (SCA, software inventory) tools

Ideally, compliance should be continuously monitored as a part of the build process.

Commercial SCA tools and services:

OSS tools that perform SCA:

Licence selection tools and resources

...

...

compatible use in software projects. The structured list and illustrations of licence relationships support GÉANT’s software development and licence compliance practices.

Core GÉANT Resources

Supporting and Background Material

Learning and Training Resources

GÉANT Courses and Workshops

Authoritative Sources

Licence Selection and Comparison

Top Lists and Brief Comparisons

Licence Compatibility

Overview of Permissive and Copyleft Licences

Image Added

Based on materials from ORCRO:

Permissive licences have simple requirements such as crediting the original work, describing changes, and providing a disclaimer. Copyleft licences (reciprocal, protective, restrictive, or, derogatorily, viral) require rights to be preserved in derivative works. Using components (libraries) with copyleft may oblige to make derived source code available, which may include the entire product or project.

  • Permissive – do anything
    • MIT – short and simple
    • ISC (OpenBSD) – further shortened equivalent
    • BSD – some variants require inclusion of disclaimer
    • Apache 2.0 – requires notice of changes, grants a licence to patents unless litigated, and preserves trademark rights
  • Weak copyleft – file or library scope
    • MPL 2.0 – simple, allows static linking and licence variants with additional terms
    • LGPL 2.1 – cleaned text of LGPL 2.0, allows dynamic linking without enforcing copyleft
    • LGPL 3.0 – grants patent use; end users must be able to install modified versions; prohibits closed devices, DRM, hardware encryption, or patent retaliation; compatible with Apache 2.0
  • Strong copyleft – project scope
    • GPL 2.0 – widely used
    • GPL 3.0 – grants patent use; users must be able to install modified software; compatible with Apache 2.0
    • AGPL 3.0 (Affero) – network-protective: external use of modified code requires its availability; network use counts as distribution
  • Proprietary – restrict user rights and protect the commercial interests of copyright holders

GPL Licence Compatibility

This diagram illustrates compatibility relationships between different free software licences. Arrows are transitive and go from the licences of components towards the licence of your project.


A chart illustrating compatibility relationships between different free software licenses.  For details, see the FSF's license list page.Image Added

(From GNU: Quick Guide to GPLv3 Compatibility)

Above, the dotted line indicates that “GPL 2 only” is not compatible with “GPL 3”, but “GPL 2 or later” is.

Image Added

(From David A. Wheeler, 2007: FLOSS Licence Slide,  SVG on Wikipedia)

Special Requirements and Risk Handling in GPL Licences

Some licences prohibit or require certain practices or behaviours, which may lead to risks of legal threats. These should be addressed or mitigated.

Frequently used protective and permissive licenses


AGPLv3

GPLv3

GPLv2.1

LGPLv3

LGPLv2.1

MPL-2

BSD

SaaS/cloud

Yes

No

No

No

No

No

No

Tivoization

Yes

Yes

No

Yes

No

No

No

Patent trolling

Yes

Yes

No

Yes

No

No

No

Proprietization

Yes

Yes

Yes

Partial

Partial

Partial

No

Granularity/reach

Project

Project

Project

Library

Library

File

N/A

Trademark grant

Yes

Yes

?

Yes

?

No

No

(From Wikipedia – Free-software licence)

EUPL 1.2 Compatibility

Image Added

(From Interoperable Europe: EUPL – Licence Compatibility, Permissivity, Reciprocity and Interoperability)

Interoperable Europe matrices and guidance:

Relationship Between the Most Used Licences in GÉANT

The following graph provides a visual overview of most frequently used  licences in GÉANT projects.

Image Added

Dual and Multi-Licensing Guidance and Implications

  • Dual and multi-licensing can help avoid licence compatibility issues, and make component use more flexible.
  • You may choose a licence compatible with that used for your software. However, you cannot dual-licence your software by matching some components with one licence, and others with another. Licences of all used components must be compatible with all your licences.

  • “Or later” (often expressed as “+”) variants imply applicability of future, possibly non-existent, versions of those licences. This is sometimes assumed unless explicitly declined.

  • Some licences include automatic relicensing (MPL 2.0, EUPL 1.2, CeCILL); EUPL lists all licences it can be combined with.

Licence Compatibility Matrices and Checkers

In-licences (component licences) are in rows and out-licences are in columns.

Image Added

(Source: GitHub – Licence Compatibility Checker)

Open Source Automation Development Lab (OSADL) Matrix and Rules

In-licences are in columns, out-licences in rows.

Image Added

(Source: Meeker & von Wendorff, 2019, Fulfilling Open Source Licence Obligations: Can Checklists Help?)
More at the OSADL site:

Creative Commons Licences Compatibility

Select two works to combine or remix. Find the first work’s licence in the top row and the second in the first column. If a check mark appears at their intersection, the works can be combined. Use the more restrictive licence (the one further right or lower in the table) for the resulting work.

Image Added

(From Wiki/CC License Compatibility)

Software Composition Analysis (SCA and Software Inventory) Tools

Commercial SCA tools and services:

OSS tools that perform SCA:

Software Bill of Materials (SBOM) tools:

  • Trivy – Generates SBOM
  • Parlay – Enriches an SBOM with third-party data

  • Syft – Generates SBOMs from container images and filesystems

  • Tern – Container analysis tool; generates SBOMs for container images and Docker files

  • CycloneDX Tool Center – Marketplace of tools and solutions to optimize and secure the software supply chain
  • Anchore Syft/Grype – SBOM generation and vulnerability analysis
  • Ortelius – Microservice SBOM and dependency tracking
  • DependencyTrack – Continuous monitoring of components and licences using SBOM input

Ideally, SCA and SBOM tools should be integrated into the CI/CD process/pipeline for continuous monitoring of dependencies and compliance.

GÉANT resources:

Other guides and tool listss:

Artefact Creation and Compliance Guides and Tools

Compliance Frameworks and Governance

EU Policy and Context

Advanced and Comparative Legal Resources

Compliance methodology