However, this has been primarily described in text. Here, we present a formal representation of the model using the Unified Modeling Language (UML). The model builds on existing components from standardization of geospatial information systems. The use of a formal notation enforces precise definition of the relationships between the components. The UML platform also supports a direct mapping to an eXtensible Markup Language (XML)–based file format, which may be used for the exchange of stratigraphic information using Web-service interfaces. The goal of this paper is to provide an information model for the geologic time scale. A formal notation is used so as to provide a rigorous description of the various elements required to describe the structure and calibration of the time scale in a manner that allows the logical consistency of the model to be evaluated. This is important, since although stratigraphic methodology is one of the most rigorously studied aspects of geological practice, it has evolved throughout the era of historical geology. There have been significant changes in best practice, in particular in the shift from characterizing units to defining the boundaries between them. Nevertheless, the time scale itself remains based on named units and eras. Other residues of earlier practice remain visible in the description of the time scale, particularly where agreement on the application of current practices is incomplete. In this context, a rigorous characterization of the relationships between the elements of the time scale, the evidence in the geologic record, and the application of specific procedures to effect numeric calibration of the scale is essential.Ī ChronostratigraphicUnit is the (notional) feature composed of all the rocks formed during the associated GeochronologicEra. ![]() Both ChronostratigraphicUnit and the commonly used LithostratigraphicUnit are kinds of GeologicUnit. Similarly, a ChronostratigraphicBoundary is the (notional) compound surface marking the upper or lower bound of a unit. Both ChronostratigraphicBoundary and LithostratigraphicBoundary are kinds of StratigraphicBoundary. In practice, the complete shape of any ChronostratigraphicUnit and ChronostratigraphicBoundary instance will not be precisely known, so while the existence of a unit and its boundaries is a fact, they will never be fully described.
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