Defining and cataloging exoplanets: the exoplanet.eu database

We describe an online database for extrasolar planetary-mass candidates, which is updated regularly as new data are available. We first discuss criteria for inclusion of objects in the catalog: definition of a planet and several aspects of the confidence level of planet candidates. We are led to point out the contradiction between the sharpness of criteria for belonging to a catalog and the fuzziness of the confidence level for an object to be a planet. We then describe the different tables of extrasolar planetary systems, including unconfirmed candidates (which will ultimately be confirmed, or not, by direct imaging). It also provides online tools: histograms of planet and host star data, cross-correlations between these parameters, and some Virtual Observatory services. Future evolutions of the database are presented.