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50 lines
2.1 KiB
50 lines
2.1 KiB
2 years ago
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\chapter{Development of \exo{}}
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The evolution of the \exo() data model has been steered by
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FE application code developers who desire the advantages of a
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common data format. The \exo{} model has been designed to
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overcome deficiencies in the EXODUS I file format and meet the
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following functional requirements as specified by these developers:
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\begin{itemize}
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\item random read/write access.
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\item application programming interface (API) -- provide
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routines callable from FORTRAN, C, and C++ application codes.
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\item extensible -- allow new data objects to be added
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without modifying the application programs that use the file
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format.
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\item {machine independent -- data should be independent
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of the machine which generated it.}
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\item {real time access during analysis -- allow access
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to the data in a file while the file is being created.}
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\end{itemize}
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To address these requirements, the public domain database library
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netCDF [3] was selected to handle the low-level data storage. The
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\exo{} library functions provide the mapping between FE data objects
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and netCDF dimensions, attributes, and variables. (These mappings are
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documented in Appendix A.) Thus, the code developer interacts with the
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data model using the vocabulary of an FE analyst (element
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connectivity, nodal coordinates, etc.) and is relieved of the details
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of the data access mechanism. To provide machine independency, the
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netCDF library stores data in eXternal Data Representation (XDR) [4]
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format.
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Because an \exo{} file is a netCDF file, an application program can
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access data via the \exo{} API or via netCDF API function calls
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directly. Although the latter two methods require more in-depth
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understanding of netCDF, this capability is a powerful
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feature that allows the development of auxiliary libraries of special
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purpose functions not offered in the standard \exo() library. For
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example, if an application required access to the coordinates of a
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single node (the standard library function returns the coordinates for
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all of the nodes in the model), a simple function could be written
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that calls netCDF routines directly to read the data of interest.
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