There are several attributes that are required to exist in a CDF if it is to conform to the NSSDC standard. These required attributes are shown in Table 2.6. Several optional attributes are also shown.
Table 2.6: NSSDC Standard CDF Attributes
The purpose of each attribute is defined as follows...
A title for the CDF data set. Only one gEntry should be written (gEntry number zero [0] for C applications, gEntry number one [1] for Fortran applications).
The field name for an rVariable. One rEntry per rVariable should be written.
The minimum valid value for an rVariable. Values below this minimum are treated as invalid or fill data. One rEntry per rVariable should be written.
The maximum valid value for an rVariable. Values above this maximum are treated as invalid or fill data. One rEntry per rVariable should be written.
The units of measurement for an rVariable. One rEntry per rVariable should be written.
The Fortran format specification to use when displaying the values for an rVariable. One rEntry per rVariable should be written.
Documentation text about the CDF. Any number of gEntries may be written.
A modification history for the CDF. Each time the CDF is modified, a new gEntry would be added with an explanation of the changes.
The scale minimum for an rVariable. This is used when scaling the rVariable's values for display. If omitted, the VALIDMIN vAttribute rEntry will be used. One rEntry per rVariable should be written.
The scale maximum for an rVariable. This is used when scaling the rVariable's values for display. If omitted, the VALIDMAX vAttribute rEntry will be used. One rEntry per rVariable should be written.
The monotonicity
of an rVariable. This specifies if the values
strictly increase ( "INCREASE"), strictly decrease ( "DECREASE"), or
are not monotonic ( "FALSE ") along a dimension or from record
to record. Specifying an rVariable's monotonicity can greatly improve the
efficiency of certain NSSDC applications (namely, the NSSDC Graphics System).
One rEntry per rVariable should be written.
A catalog description for an rVariable. This is used for cataloging purposes by some NSSDC applications. One rEntry per rVariable should be written.
The fill value for an rVariable. This value should not be confused with the pad value that may be specified for an rVariable (with the Internal Interface) that the CDF library actually uses when writing records. The values should agree but the FILLVAL vAttribute is not used by the CDF library in any way. It is, however, used by CDF applications (including the CDF toolkit). One rEntry per rVariable should be written.