Open Content Licenses
Open Content Licenses covers Creative Commons, public-domain dedications, and the free-culture test - for text, images, data, and educational material rather than code.
The CC building blocks
Four conditions combine into six licenses: BY (attribution), SA (share-alike), NC (non-commercial), ND (no derivatives).
- CC BY, CC BY-SA, CC BY-NC, CC BY-ND, CC BY-NC-SA, CC BY-NC-ND.
- CC0 is a public-domain waiver, not a license, and is the usual choice for data meant to be reused without conditions.
- Attribution follows TASL: Title, Author, Source, License, with links where practical. Version 4.0 adds a 30-day cure period for accidental violations.
What counts as free culture
A license qualifies as a Free Cultural Works license if it permits use, modification, and redistribution for any purpose. CC BY, CC BY-SA, and CC0 qualify; NC and ND do not, because they restrict use or adaptation. The GFDL qualifies when no invariant sections are used; ODbL is the copyleft option for databases and is used by OpenStreetMap.
Combining material
- SA requires adaptations to carry the same license or a compatible one. CC BY-SA 4.0 is one-way compatible with GPLv3; versions 2.0 and 3.0 are not.
- NC cannot be combined with SA: NC adds a restriction, and SA forbids additional restrictions.
Worked example
A school wants to place CC BY-NC photographs inside a CC BY-SA 4.0 textbook. The reasoning: the textbook carries SA, which promises every downstream user the same freedoms; NC withholds commercial-use permission, so the two cannot coexist in one licensed work. The options are to obtain a BY-SA or commercial relicense from the photographer, or substitute CC BY, CC BY-SA, or CC0 images. Crediting the photographer does not fix the conflict.
Traps
- Treating CC0 as a license, or assuming it clears patents and trademarks.
- Assuming NC means "schools are always fine"; the term is deliberately vague and restricts use, not users.
- Forgetting that ND blocks remixing and that SA applies to adaptations.
- Omitting TASL elements when reusing material.