Use the generic gml:DefinitionType for basic Phenomenon definitions, gml:description may be used for a more extensive description of the semantics, with a link to a definitive version (if available). gml:name should be used for the "short name" or label. SamplingSite implements a characterisation of the Feature of Interest, through a set of observations. The key implication is that the location of the site and the observation procedures provides for a representative sample of the actual feature, within the scope of the sampling regime (e.g. a time period) This is a view of the sampling feature that contains no observations, and can be used simply to map the spatial location, access identify and metadata etc. time-instant coverage which samples a property of the feature of interest at different times A view of the sampling feature with some subset of the constrained observations, where the result set is a trend over the sampled time envelope.