Associating metadata with timeseries as a whole and at each individual point is a common requirement in hydrological data. Data is annotated with various types of qualifying information such as quality assertions, affecting environmental conditions, description of processing and so on. These annotations are important when processing and analysing timeseries to ensure correct interpretation. <br /></p><p>At a generic level it is possible to associate any metadata with timeseries and timeseries points, this is shown with Annotation associations in Figure 21 and Figure 22. Using a soft-typed approach, this is simply a collection of named value pairs. Whilst flexible, this approach doesn’t capture semantics specific to the metadata elements. WaterML2.0 thus defines two specialisations for timeseries and point-based metadata as shown in Figure X and Figure X. <br /></p><p>Using the interleaved structuring, metadata is associated with a time-value pair explicitly, with the metadata directly associated with a pair. <br /></p><p>Using the domain-range structuring, metadata is associated to the timeseries through an AnnotationCoverage. This is a coverage that describes the temporally ranging metadata for the series. The domain of the coverage is the time that the annotation is valid; the range captures the values of the annotation (e.g. a quality assertion). In ISO19123 the values of range are described using a Record, which is a generic set of typed values. Each annotation that is required would need an associate record type. For example, quality may be a string record type that allows for simple categorical representations of quality. <br /></p><p>The core elements of annotation for timeseries and timeseries points are shown in ???? and ????. These types are further extended for specific series types (e.g. measurement series.)<br /></p><p>Each of the metadata elements is described in the following sections. <br /></p>