Mother class that contains the basic support for any element inside a source catalogue. That implies an identifier, a position and, possibly, a classification using a SKOS element. <Enter note text here> As a consolidation of different source detections (from one of more catalogues), general entities called source are generated. For these entities, other quantities can be defined, e.g. the proper motions (tranversal velocity of the sources on the sphere) that imply different detections and a crossmatch of the different source detections. <Enter note text here> <Enter note text here> <Enter note text here> Messurements that implies more than one detection to be obtained and, at least, one crossmatch. Examples are distance or proper motion. A crossmatched source COULD contain a radial position describing the measurement of the distance to the object. Distance that can be expressed in two ways: as a distance and as a parallax. <Enter note text here> A crossmatch source COULD contain a properMotion element describing the velocity on the sky (imaginary fixed background) as seen from the center of mass of the Solar System, as compared to the imaginary fixed background of the more distant stars. It is usually express as a vector of two components, describing the variation of the position on certain sky coordinates (in general right ascension and declination), corrected by declination and expressed on mas/year. <Enter note text here> <Enter note text here> Messurements that can be obtained in one single source detection. Examples are postion and radial velocity (through spectroscopy) A Source object COULD contain a radialMotion associated object with that contains the calculation of the tangential velocity of the source detection. Usually done through spectroscopic calculations. Object describing the source position in the sky in the 3D space. It is described by a spatial coordinate object, reused from STC, a spatial coverage (specially for extended sources). See IVOA STC document for details. <Enter note text here> <Enter note text here> Unique identifier for this detection within the source catalogue. As a crossmatched source is a result of a combination of different detections or sources from different catalogues, the structure contains a main identifier and a set of aliases. <Enter note text here> <Enter note text here>