Olson, Arthur David (NIH/NCI) [E] said:
There's no license.
At least in English (and Scottish) law, the copyright holder of any written material (like this) has the right to prevent any other person from copying it. A licence is a written (and it must be written) agreement or statement giving other people permission on stated terms (e.g. a payment per copy). One can issue a licence that says anyone can copy it without any payment being required provided that they retain one's name on it. I note that the TZ data and code has several authors; in principle every one of them would need to do this. Again, at least in English and Scottish law, there's a doctrine of estoppel by acquiesence. The data has been distributed without practical restriction for so long that a court would not support a claim for infringement of copyright at this point. However, that would not necessarily apply to new versions. The best solution would be to explicitly attach a Creative Commons licence to the data and code, plus a notice that any contributions are accepted on the terms that the licence extends to them as well. For the record, I accept that any contribution I may have made may be copied on the same terms as the rest of the TZ package. -- Clive D.W. Feather | If you lie to the compiler, Email: clive@davros.org | it will get its revenge. Web: http://www.davros.org | - Henry Spencer Mobile: +44 7973 377646