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If I release a program specification [1] under the AGPL, and the program itself under the AGPL, the two are obviously compatible: I can develop them at the same time, copy text (for example, method headers) between them freely, "derive" methods from the spec requirements, back-derive requirements from implementation (it happens, ok ;). But, the specification would not be compatible with BY-SA works (say, Wikipedia or Stack Exchange).

If I release the specification under BY-SA instead, it is still compatible in one direction (from spec to software), because BY-SA is one-way compatible with the GPL [2], and the GPL is compatible with the AGPL.

But, if I release the specification under BY-SA (including releasing it before the software), am I "losing" any of the copyleft strength of the AGPL. i.e. enabling someone to create a non-copyleft work where they couldn't before?

(Looking at it another way, if I release just an AGPL specification, am I guaranteeing that any implementation must be AGPL? Or is anyone free to develop the "ideas" in the spec under any license they want?)


[1] To clarify, a specification is not end-user documentation (a manual), it is a (sometimes very detailed) outline and plan for what the software must do.

The answer obviously rests on the judgment of to what extent the code is a derivative work of the specification. I will obviously accept an answer of "it depends", "not tested in law", etc, if that is the most accurate answer possible :D

[2] It appears I am dreaming and this is underway, but not yet finalised. Let's assume for the sake of argument we are a few months in the future and it's true.

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    The documentation and the code don't form a combined work in any usual interpretation (i've never heard of it). You should be good making different licenses. – Martijn Aug 14 '15 at 13:41
  • @Martijn I've clarified what I mean by specification – david.libremone Aug 29 '15 at 9:33
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The AGPL is a software license. It doesn't work well for media content like documentation. Even the FSF does not recommend to use the GPL-family licenses for documentation. The AGPL is even worse than the GPL, because its addition to the GPL, clauses for using the software over a computer network, is even more nonsensical when it comes to documentation.

The FSF recommends the GNU Free Documentation License for documentation.

I am not a lawyer, but by offering the documentation under other conditions than the software itself you will likely not weaken your rights on the software, because documentation and software are independent creative works.

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A specification is a document describing some programs, in many cases interfaces. Regarding the implication of the licenses: it is relevant what implementing a specification does. I don't know about any law-suits indicating that the implementation of a specification is forming a derivate or even violating the copyright of the author of the specification. That might be the case though, because most authors of specifications intend it to be implemented multiple times.

So if we assume that implementations of the specification can be done without being influenced by the license of the specification, then we can conclude the following: If the implementation is based on your implementation (licensed AGPL) it must be licensed AGPL. If the implementation is independent, it can have any license its author chooses. So how you license the specification only affects direct derivates of this specification (for instance extensions to the specification). As both AGPL and CC-BY-SA are copyleft-licenses the differences are small. Relevant here is, that AGPL is a license for software, many clauses don't make sense for a document. So I would recommend to license it as CC-BY-SA.

Having software under one license and documentation for it under another doesn't implicate any compatibility-problems (you said that having both under AGPL is compatible).

  • I've clarified I mean by compatibility in this scenario (some of which may or may not hold) – david.libremone Aug 29 '15 at 9:35
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For a recipient to effectively exercise freedom to make modified versions of a work, it is necessary that they have access to the digital information that is preferred for making such a modified work.

Without the source form of the work — that is, whatever digital form of the work is preferred for making modifications to that work — the recipient is artificially hindered in their freedom to make modifications on a par with what they received.

The AGPL guarantees that freedom by requiring such distributors to make available the complete corresponding source form of the work. The recipient can request the source form, which is the preferred form of the work for making modifications to it.

There is no Creative Commons license which has such a requirement to make the source form of the work available. That's a benefit which would be lost by choosing CC By-SA for a work.

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