How is 'renting' of ebooks from libraries handled?

The expiration date is set using the digital rights management. The item does not need to be returned as after a number of days or views, it can't be accessed anymore.

A system that, for the first time, allows libraries to manage the sales, rent and loaning of ebooks is being rolled out in Denmark. The Ebog platform allows ebooks to be available either as entire texts or on a chapter by chapter basis, and enables the material to be rented within any given time span. The library loan is executed with an eight-day loan period; re-loan is available on expiry. Unlike any other digital lending service in current use, this "revolutionary technology" allows librarians and users of the library catalogue system to search for ebooks alongside printed books. Payment is on a pay-per-use basis, as with printed books.
(http://www.bookbrunch.co.uk/index.php?option=com_content&task=view&id=557&Itemid=83