GPL and closed source

Chuck Swiger chuck at
Mon Jun 6 20:23:49 UTC 2011

On Jun 6, 2011, at 8:47 AM, Mahesh T. Pai wrote:
> David Woolley said on Mon, Jun 06, 2011 at 08:13:24AM +0100,:
>> No. If you really want to do this, the accepted way is to create two
>> programs that communicate by a documented message passing protocol
>> (TCP or pipes are typically used, and command line options can be
>> part of the calling interface.)
> So, how exac[t]ly would a judge interpret an API? 

In the US, the major decision was Computer Associates v. Altai:

...which defined an "abstraction-filtration-comparison" test.

The filtration test requires one to analyze the program modules via a flowchart, and decide whether each distinct module or section "shows only an idea" (if yes, the material is not copyrightable, but might be patentable), or is an expression of an idea.  If the latter, the analysis requires consideration of whether the expression is (a) dictated by efficiency, (b) dictated by external factors (specifically interfaces, APIs), or (c) whether the expression is taken from the public domain. Unless the answer to (a)-(c) are all no, and the code does not represent a "protected combination", and unless it constitutes "enough copying to be a wrongful taking", it is considered "lawful copying" and not "copyright infringement".

Notice (b) & (c) in particular; publicly published APIs generally cannot qualify or be used as grounds for software copyright infringement.


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