Free and open-source licences
The freedoms of free software, the difference from freeware and the public domain, the main licence families (permissive, weak and strong copyleft, AGPL), their obligations, SPDX identifiers and Creative Commons licences.
- 24 cards
- 4 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
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- Scenarios
A few cards from the deck
Free software: what is it?
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Software whose licence grants the user four freedoms: to run it for any purpose, study and adapt it, redistribute it and distribute modified versions.
"Free" does not mean "no cost": free software can be sold. Software at no cost but closed is not free.
A proprietary application distributed to customers includes a library under
GPL-3.0. What does the licence require?- Distributing the whole under GPL-3.0, source included
- Nothing: the GPL only covers changes to the library
- Only a mention of the authors, as with the MIT licence
- A copyright notice in the product's documentation
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Distributing the whole under GPL-3.0, source included
Strong copyleft extends to the derived work: the application incorporating the library must be redistributed under the GPL, with its source. Simple attribution duties belong to permissive licences.
The four freedoms of free software are: run for any purpose, … (which requires access to the source code), … copies, and distribute your modified versions.
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The four freedoms of free software are: run for any purpose, study and modify (which requires access to the source code), redistribute copies, and distribute your modified versions.
Without the source code you cannot study or adapt a program: access to the code is a condition of the freedoms, not a bonus.
Copyleft: what is it?
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A licence clause that requires modified or derived versions to be redistributed under that same licence.
It turns copyright against appropriation: the freedoms pass on with each redistribution. It is strong (GPL), weak (LGPL, MPL) or extended to networks (AGPL).
A start-up modifies a library under the AGPL and uses it in its online service, distributing nothing. What obligation arises?
- Offer the modified code to the service's users
- None: with no distribution, no obligation arises
- Only keep the copyright notice
- Pay the library author a royalty
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Offer the modified code to the service's users
The AGPL adds to the GPL an obligation triggered by network access: offering the service is treated like distributing. This is exactly the gap in the GPL that this licence set out to close.