NetCDF and CF Conventions as Formal Standards

Efforts to recognize netCDF and the CF Conventions as international standards

NetCDFNetCDF (Network Common Data Form) refers to a data model for array-oriented scientific data; a freely distributed collection of access libraries implementing support for that data model; and a machine-independent, self-describing data format. Together, the interfaces, libraries, and format support the creation, access, and sharing of scientific data. For many communities, the Climate and Forecast (CF) conventions for netCDF have served as a de facto interoperability standard, but one that has never been recognized by a formal standards body.

Recently, members of the netCDF community have initiated efforts to establish netCDF as a formal standard. These efforts involve both the Open Geospatial Consortium (OGC) and the NASA Earth Science Data Systems Standards Process Group (SPG).

Two initiatives are underway in the OGC. Within the Web Coverage Service (WCS) community, the CF-netCDF combination is being proposed as a data delivery extension to the WCS core. Independently, a CF-netCDF Standards Working Group has been established, with the goal of making CF-netCDF an OGC standard for binary encoding, enabling its use in data services protocols other than WCS. The Web Feature Service and Sensor Observation Service are two examples. This effort to establish a separate OGC netCDF encoding specification is complementary to the netCDF extension to WCS, and is being carried out in collaboration with the WCS standardization group.

Within NASA, the NetCDF Classic and 64-bit Offset File Formats Standard has been formally recognized by the NASA SPG, thereby providing a well documented, widely accepted reference for the netCDF format. In addition, two efforts are underway to recognize the CF (Climate and Forecast) Conventions as a formal NASA standard for encoding georeferenced data in binary form. The draft NASA standard for the CF Metadata Conventions is now under review and available for download.

The OGC recently adopted a modular form for its standards where each specification has a core and a set of extensions. For the netCDF, the plan is initially to establish netCDF Classic abstract data model as the core with the binary encoding as first extension. That extension will be based on the already adopted NASA SPG netCDF file format standard. A second extension covering the CF conventions follows. This approach ensures that the standard is backwards compatible with existing netCDF and CF documents and implementations already in widespread use within the extensive netCDF user community. This core with two extensions will form the foundation, but other extensions may follow – possibly including extensions for the enhanced data model; ncML-GML, HDF5, and other encodings, as well as the netCDF APIs (Application Programming Interfaces).