Open Database Licence, an attempt to create an open licence for data which covers the ‘database rights’ as well as copyright itself. It does this by imposing contractual obligations on the data re-user. Unfortunately [1] contract law is fundamentally different from copyright law, since copyright is inherent in a work and binds all downstream users of the work, whereas a contract only binds the parties to the contract and has no force on a later re-user of re-published data. The ODbL remains useful nevertheless, and other attempts are being made to create open licences specifically for data.

Source: ODH