Design and implementation of netCDF markup language (NcML) and its GML-based extension (NcML-G(ML))

The Network Common Data Form (netCDF) is one of the primary methods of self-documenting data storage and access in the international geosciences research and education community and beyond. NetCDF was designed for use in a networked environment. The recent evolution toward web services approaches to data exchange has focused attention on communication via messages in the defacto standard XML language. XML is a text-based language while netCDF is based on a binary file storage mechanism; thus NcML is a natural augmentation of netCDF with extensions encapsulating descriptions of the structure and content of netCDF objects in an XML form. Since netCDF was designed to be self-documenting, the XML representation of internal netCDF documentation is a natural augmentation of the original netCDF concept. In fact, the netCDF Markup Language (NcML) and NcML-G (NcML-Geography) extensions described in this article have applications beyond merely representing the internal netCDF documentation in the XML language. The NcML coordinate system makes it possible to describe the coordinate system used to represent the netCDF dataset. Furthermore the NcML dataset is a tool for describing "virtual netCDF" files that may be aggregations of data from several existing netCDF files, or it can represent a target dataset to be created by transforming existing netCDF files into a new form described in the NcML language. The NcML-G extension provides a means for fusing the data models of the traditional netCDF atmospheric science community with those of the GIS community which is of the utmost importance. Bringing the data models and data systems of those communities together will foster an era of interdisciplinary research and education within the geosciences subdisciplines. It will also encourage closer interactions between the geosciences and the societal impacts community. The design and software implementation of the core NcML specification and its extensions are presented and discussed