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The development of the netCDF interface began with a modest goal related to Unidata's needs: to provide a common interface between Unidata applications and ingested real-time meteorological data. Since Unidata software was intended to run on multiple hardware platforms with access from both C and FORTRAN, achieving Unidata's goals had the potential for providing a package that was useful in a broader context. By making the package widely available and collaborating with other organizations with similar needs, we hoped to improve the current situation in which scientific software is only rarely reused by others in the same discipline and almost never reused between disciplines (Fulker, 1988).
Important concepts employed in the netCDF software originated in a paper (Treinish and Gough, 1987) that described data-access software developed at the NASA Goddard National Space Science Data Center (NSSDC). The interface provided by this software was called the Common Data Format (CDF). The NASA CDF was originally developed as a platform-specific FORTRAN library to support an abstraction for storing multidimensional scientific data.
The NASA CDF package had been used for many different kinds of data in an extensive collection of applications. It had the virtues of simplicity (only 13 subroutines), independence from storage format, generality, ability to support logical user views of data, and support for generic applications.
Unidata held a workshop on CDF in Boulder in August 1987. We proposed exploring the possibility of collaborating with NASA to extend the CDF FORTRAN interface, to define a C interface, and to permit the access of data aggregates with a single call, while maintaining compatibility with the existing NASA interface.
Independently, Dave Raymond at the New Mexico Institute of Mining and Technology had developed a package of C software for UNIX that supported self-describing scientific data along with a "pipes and filters" approach to processing, analyzing, and displaying scientific data. This package also used the "Common Data Format" name, later changed to C-Based Analysis and Display System (CANDIS). Unidata learned of Raymond's work (Raymond, 1988), and incorporated some of his ideas, such as the use of named dimensions and variables with differing shapes in a single data object, into the Unidata netCDF interface.
In early 1988, Glenn Davis of Unidata developed a prototype netCDF package in C that was layered on a nonproprietary external data representation standard (XDR) developed by Sun Microsystems. This prototype proved that a single-file, network-transparent implementation of the CDF interface could be achieved at acceptable cost and that the resulting programs could be implemented on both UNIX and VMS systems. However, it also demonstrated that providing a small, portable, and NASA CDF-compatible FORTRAN interface with the desired generality was not practical. (NASA's CDF and Unidata's netCDF have since evolved separately, but recent CDF versions share many characteristics with netCDF.)
In early 1988, Joe Fahle of SeaSpace, Inc. (a commercial software development firm in San Diego, California), a participant in the 1987 Unidata CDF workshop, independently developed a CDF package in C that extended the NASA CDF interface in several important ways (Fahle, 1989). Like Raymond's package, the SeaSpace CDF software permitted variables with unrelated shapes to be included in the same data object and permitted a general "hyperslab" form of access to multidimensional arrays. Fahle's implementation was used at SeaSpace as the intermediate form of storage for a variety of steps in their image-processing system.
After studying Fahle's interface, we concluded that it solved many of the problems we had identified in trying to stretch the NASA interface to our purposes. In August 1988, we convened a small workshop to agree on a Unidata netCDF interface, and to resolve remaining open issues. Attending were Joe Fahle of SeaSpace, Michael Gough of Apple (an author of the NASA CDF software), Angel Li of the University of Miami (who had implemented our prototype netCDF software on VMS and was a potential user), and Unidata systems development staff. Consensus was reached at the workshop after some further simplifications were discovered. A document incorporating the results of the workshop into a proposed Unidata netCDF interface specification was distributed widely for comments before Glenn Davis implemented the software it described. Comparison with other data-access interfaces and recent experience in using netCDF are discussed in (Rew and Davis, 1990a) and (Rew and Davis, 1990b).
In October 1991, we announced version 2.0 of the netCDF software
distribution. Slight modifications to the C interface (declaring
dimension sizes to be long rather than int) improved the
usability of netCDF on inexpensive platforms such as MSDOS computers,
without requiring recompilation on other platforms. This change to the
interface required no changes to the associated file format.
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