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My friend and I are planning to develop a tiny and simple CMS by taking some inspirations from an already existing GNU GPL CMS.

We take the ideas and try to develop it as simply we can, is it possible ? We are planning to set up the same licence, GNU GPL. Is it a good choice ?

Which are the conditions to do it ?

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You can take all the ideas you want, unless they're patented. Copyright doesn't cover ideas or functional elements.

A quick test for whether you can take something or not is this: Can you easily replace the thing you are taking with a thousand other things that would all work just as well? If so, it is expressive, and you may not take it (instead, do one of the other things that work just as well). If not, it is functional, not expressive, and you may take it.

(Consult a lawyer if you need actual legal advice!)

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Thanks :) Well the feature i want to take is "importing from excel files with specific format" without visualisation and i want to do the same but : i am using text files then i am able to visualize it on my website before submit it on my bdd, also a specific user can valdate it to have a final statut (validate and publish) is it so close to the initial idea ? – Zeroth Aug 23 '11 at 13:21
I'm not 100% sure I follow you, but that sounds like pure function to me. There aren't 1,000 equally good ways to accomplish the same function, so it's an idea. – David Schwartz Aug 23 '11 at 13:28
You can't Patent an Idea – Jarrod Roberson Aug 23 '11 at 13:44
The article explains that you can't patent a "mere idea". But patents fundamentally protect methods of accomplishing things, which are a type of idea. – David Schwartz Aug 24 '11 at 6:07

I am not a lawyer and I am not an expert on the GPL, but;

If I've understood your question correctly you are planning on releasing your work (project A) under the GPL, and want to use some ideas from another project (project B) which was released under the GPL, is this the case?

If so then I think that you can use as much or as little of project B as you wish, including source and the only extra thing you would need to do is credit Project B in the docs and source.

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Not including source. Including significant amounts of source makes it into a derived work and, therefore, must be released under the GPL terms. – David Thornley Aug 23 '11 at 14:01
Yes exactly. I take some ideas from B to adapt to A project. I think i will took some sources, but most of them will be adapted to my project. and it will also be under GPL terms. – Zeroth Aug 23 '11 at 14:18
@David Thornley The OP stated We are planning to set up the same licence, GNU GPL. So it doesn't matter if it is a derived work. – Paul Aug 23 '11 at 15:44

You can't Patent an Idea, Patents cover inventions, in other words implementations of ideas. Ideas are free to re-implement as long as it is a clean room implementation.

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A clean room implementation will protect you from copyright infringement issues, but (at least in most countries) not from patent infringement issues. If your product does/embodies the limitations of a patent claim, a "cleanroom" implementation will not protect you from a claim of patent infringement. – Jerry Coffin Aug 23 '11 at 14:13
I don't get what "clean room" implmentation means exactly. for example ideas/methods are to use "import data from format files to db" Project A : using excel files with Project A syntax format using colums Project B(mine) : using txt files or textarea with my specific format, using regexp/parsing to detect syntax error and statut decision(invalid, valid, publish,accept) Am i on a "cleanroom" ? – Zeroth Aug 23 '11 at 14:24
The question is about copyright, not patents. – tdammers Aug 23 '11 at 14:29
If only this was true Jarrod. Unfortunatly this is what the law says not what the courts enforce. You can now patent a vague process that covers practically everything then sue retroactively. – Chad Aug 23 '11 at 14:37
@Zeroth - That would be a process that could be covered by a patent. The specific implimentation of that process that is used by another product would be copyrighted. If you do the import your own way then it is your way and you are entitiled to that copyright. If you "Borrow" code from someone else it is best to get permission and/or follow the licencing agreement. – Chad Aug 23 '11 at 14:44

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