Defensive publication and prior art databases
One way to invalidate a patent is to find prior art - an example of the idea that pre-dates the patent. Publishing prior art is a common business strategy. The most known publication to this effect is the IBM Disclosure Bulletin, but other companies like ASEA has used it extensively. By publishing ideas you block others from patenting what is already then known.
Whether it is better or worse for Free Software to make it easy to find prior art is a subject of much discussion as the question whether published source code may be regarded as prior art.
 Limits to effectiveness
- Sometimes there is no prior art.
- Sometimes the prior art only eliminates part of the patent. The patent holder will be permitted to redraft their patent to keep the non duplicated parts while avoiding the prior art you've found.
- This can backfire if the database is public because patent applicants could use the database to see what changes are necessary (the smallest changes possible) to avoid being similar to the prior art, so they won't have to worry about their patent being invalidated.
 Defensive publication
Defensive publication is the idea that by documenting and publishing an idea, you can prevent the future problem that someone else will patent that idea.
For example, in 2004, a paper was published on "Precise detection of memory leaks". In 2007, a patent application was filed at the USPTO for a follow-on invention. The 2007 application cited the 2004 paper as being part of the state-of-the-art which is extended by the patent application. The authors of the 2004 paper have no connection to the authors of the 2007 patent application. Ironically, one of the authors of the 2004 paper is a prominent member of anti-swpat group FFII.
 Related pages on en.swpat.org
- Duds and non-solutions
- Invalidating the most harmful - searches for prior art are sometimes used in this targeted way
- Open Invention Network - their "defensive publication" programme is basically a prior art database
- Publishing information is made dangerous - about the dangers
- Public Domain Ideas, and their wiki's category for Computer Software, Algorithms, and Data Processing
- Defensive Publications - a project of Linux Defenders
- Linux Foundation discussion of how to implement this technically
- Best practises for writing defensive publications, Aug 2012, Sebastian Kügler
 About the down sides
- Analysis of the problems of defensive publication, FFII
- "Defensive Publishing" No Thank You!, FFII
- A study by David Martin showing that trolls do patent around published ideas (published patents) in the USA - this is likely to be just as true for defensive publications
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