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Open Source

The definition of Open Source is somewhat longer than that of Free Software. The Open Source Definition states the explicit rules, but these are the 10 basic points:

  1. The license must allow free or paid-for redistribution.
  2. The program must include source code.
  3. Derived works must be redistributable under the same terms.
  4. The source code may be distributed under a license that doesn’t allow distribution of modified versions only if distribution of patches is allowed.
  5. The license must not discriminate against any people or groups.
  6. The license must not discriminate against any activities.
  7. All rights granted to the original user of the code must also be granted to anyone who receives a copy of the code from that user.
  8. The license must cover the program in isolation, and may not be dependent on bundling.
  9. The license may not place restrictions on any software other than that being distributed under the license.
  10. The license must be technology-neutral.

Now let’s compare these requirements to those of the Four Freedoms:

  • The license must allow free or paid-for redistribution. Rule 1 is covered by freedom 2.
  • The program must include source code. Rule 2 isn’t stated explicitly by the Four Freedoms, but is a requirement for freedoms 1 and 3.
  • Derived works must be redistributable under the same terms. Rule 3 isn’t stated explicitly in the Four Freedoms, but could be thought of as being implied by freedoms 2 and 3. Freedom 2 requires you to be able to redistribute the code, and freedom 3 requires the ability to distribute derived works. Rule 3 doesn’t state explicitly that the distributed copy must also be Free Software, but this stricture can be inferred.
  • The source code may be distributed under a license that doesn’t allow distribution of modified versions only if distribution of patches is allowed. Rule 4 is part of freedom 4. You must be able to distribute your improvements. Whether you do this via patches or via a modified copy of the source isn’t stated explicitly.
  • The license must not discriminate against any people or groups (rule 5), the license must not discriminate against any activities (rule 6), and the license must be technology-neutral (rule 10) all come under the heading of freedom 0; anyone must be able to use the software, in any way, for any purpose.
  • All rights granted to the original user of the code must also be granted to anyone who receives a copy of the code from that user. Rule 7 falls into the same category as rule 3; it’s only implied by the Free Software Foundation’s Four Freedoms.
  • The license must cover the program in isolation, and may not be dependent on bundling (rule 8) and the license may not place restrictions on any software other than that being distributed under the license (rule 9) are slightly stricter than the rules of the Free Software definition. Rule 8 could be seen as part of freedoms 2 and 3, but it’s not stated explicitly.

In general, if a program is Free Software, it’s also Open Source, and vice versa.

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