Schematic representation of the S17 catalogue creation. Set 1 represents the AllWISE database; set 2 the SDSS spectroscopic observations; set 3 objects with optical photometry (not limited to SDSS); set 4 sources present both in AllWISE and optical photometric catalogues but which do not have spectra; set 5 sources included in S17 anomaly catalogue; set 6 sources used as a training sample for the OCSVM algorithm. The ellipses do not reflect the sizes of the databases.