My Swiss lawyer colleague also explained the following, which I also think is helpful for everyone. The first explanation I posted, is effectively an expansion of the second paragraph below.
"Licenses allow the use of absolute rights, which means rights that are enforceable against everybody. Such absolute rights are, for example, ownership (with respect to material goods), patents (with respect to inventions), copyright (with respect to works of art and literature [in a very broad sense]). Where there is no absolute right, there is no room for a license.
Data is an immaterial good. Ownership never applies to immaterial goods. A license would be possible, if the data is patentable or copyrightable. This is possible in some cases, but not regularly. Where data is just data there is no license.
It is possible that you keep your data secret and that nobody has access to them. Then you can allow access individually. A lawyer would call such an allowance a “use agreement”, but not a license. It is only enforceable against the contract partner, but not against anybody else. If another person finds access to these data, you cannot impede that person from using them.
Personal data about yourself is still a completely different case. There is also an absolute right, which is called “privacy” in some legislations, or “personal right” in others. It does not give you ownership over these data, but the right to prevent others from certain uses of these data. At the same time, others (for example the police) are allowed to make use of the very same data. That’s why the term of “ownership” is inappropriate for the relation between you and these data."