In principle, as long as the national law says, but the minimum requirement under the Berne Convention is 50 years. The term is calculated from the end of year of the author’s death which is more practical.
In copyright law, a derivative work is an expressive creation that includes major copyright-protected elements of an original, previously created first work (the underlying work). The derivative work becomes a second, separate work independent in form from the first.
Related rights are rights that in certain respects resemble copyright. The purpose of related rights is to protect the legal interests of certain persons and legal entities who contribute to making works available to the public. One obvious example is the singer or musician that performs a composer's work to the public. The overall purpose of these related rights is to protect those people or organizations that add substantial creative, technical or organizational skill in the process of bringing a work to the public.