The Open Database License (ODbL) is an open license for data and databases which gives users freedom to use, reuse and redistribute subject only to the requirement of attribution and share-alike. This license, the first of its kind, is a major step forward for open data. There are currently very few licenses available suited to data and databases and none which provide for share-alike (existing share-alike licenses such as the GPL, GFDL and CC By-SA are all unsuitable for data). - Tom Keays