The recent decision by the New Zealand Parliament to rule out software patents has led some to query whether the committee that agreed to this might have been swayed more by the strength of lobbyists than by any rational arguments. This is not helped by the language used in the committee's own report, which out of necessity, summarises their considerations into a brief paragraph. It even appears to some that the committee accepted an argument that there is no "inventive step" in software development.
The actual argument is that the "inventive step" is in the algorithm; the code is simply the implementation of that "inventive step." As algorithms cannot be patented in New Zealand, it follows that code should not be either.
A good way to think about this is in comparison with books/films and plots. There are multiple books/films with the same plot - Hollywood depends on that. Each book/film has copyright, whereas the plot of a book/film cannot be patented. Software is just the same - an encoding of an underlying algorithm, which should not be patentable, just as movie plots are unpatentable.
Software attracts copyright as does books/films and copyright is a perfectly clear and defensible legal right. In jurisidictions that allow software patents, software is the only art that can attract both copyright and patents, an unnecessary duplication.
Of course this is only one half of the argument. The other half is entirely pragmatic, acknowledging the ease with which people can get patents awarded for completely obvious claims and recognising the great harm that software patents, trivial or not, have done to innovation and competition.
So, rather than the committee having been bewildered by technical arguments they did not understand, they did that rarest thing for legislators - they listened carefully to the arguments and did the right thing.
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