IANAL, but I'm not actually sure datasets like these CAN be copyrighted. Copyright rewards "original creative expression", (Feist v. Rural Telephone Service) not just effort, and I know things like phone books and other databases aren't protected by copyright. Generally, compilation protection is limited to things like charts and graphs, were the author has actually shown creative input into how the data is presented or displayed.

EDIT: But just to be sure, I would recommend something is well understood and is aimed towards a general usage, such as a Creative Commons license of your choice http://creativecommons.org/choose/