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Next: NetCDF-4 Classic Model Format, Previous: File Format, Up: File Format
The netCDF-4 format implements and expands the netCDF-3 data model by using an enhanced version of HDF5 as the storage layer. Use is made of features that are only available in HDF5 version 1.8 and later.
Using HDF5 as the underlying storage layer, netCDF-4 files remove many of the restrictions for classic and 64-bit offset files. The richer enhanced model supports user-defined types and data structures, hierarchical scoping of names using groups, more primitive types including strings, larger variable sizes, and multiple unlimited dimensions. The underlying HDF5 storage layer also supports per-variable compression, multidimensional tiling, and efficient dynamic schema changes, so that data need not be copied when adding new variables to the file schema.
Although every file in netCDF-4 format is an HDF5 file, there are HDF5 files that are not netCDF-4 format files, because the netCDF-4 format intentionally uses a limited subset of the HDF5 data model and file format features. Some HDF5 features not supported in the netCDF enhanced model and netCDF-4 format include non-hierarchical group structures, HDF5 reference types, multiple links to a data object, user-defined atomic data types, stored property lists, more permissive rules for data object names, the HDF5 date/time type, and attributes associated with user-defined types.
A complete specification of HDF5 files is beyond the scope of this document. For more information about HDF5, see the HDF5 web site: http://hdf.ncsa.uiuc.edu/HDF5/.
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