It is now conventional to make a distinction between what libraries own (e.g. books, DVDs, ...) and what they license (e.g. e-journals).
However, we can only use 'own' in a circumscribed way. This has been made clearer in the mass digitization projects. Libraries cannot do as they wish with the digitized copies of copyrighted material. And we know that in most library collections, a large part, maybe a majority part, is still covered by copyright.
What the library in fact 'owns' is the cost of managing the physical materials and of making them available to users. They do not 'own' the content, and are limited in what they can do with it.
In fact, they may end up licensing the very content that they thought they owned once it has been digitized.