Changes between Version 8 and Version 9 of markhDataModelDrafting


Ignore:
Timestamp:
01/15/14 09:51:32 (5 years ago)
Author:
markh
Comment:

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  • markhDataModelDrafting

    v8 v9  
     1=== Properties ===
     2
     3Properties recognised by the CF data model correspond to attributes listed in the CF for NetCDF files: Appendix A.
     4
     5 * standard_name
     6  * a controlled vocabulary - the value must be a valid vocabulary item (http://cf-pcmdi.llnl.gov/documents/cf-standard-names/)
     7  * valid for:
     8   * field
     9   * dimension coordinate
     10   * auxiliary coordinate
     11   * cell measure
     12 * units
     13  * a controlled vocabulary - the value must be a valid vocabulary item (http://www.unidata.ucar.edu/software/udunits/)names/)
     14  * valid for:
     15   * field
     16   * dimension coordinate
     17   * auxiliary coordinate
     18   * cell measure
     19 * comment
     20  * valid for:
     21   * field
     22 * history
     23  * valid for:
     24   * field
     25 * institution
     26  * valid for:
     27   * field
     28 * long_name
     29  * valid for:
     30   * field
     31   * dimension coordinate
     32   * auxiliary coordinate
     33   * cell measure
     34 * references
     35  * valid for:
     36   * field
     37 * source
     38  * valid for:
     39   * field
     40 * standard_error_multiplier
     41  * valid for:
     42   * field
     43 * title
     44  * valid for:
     45   * field
     46 * axis
     47  * In a field, a given value of the axis attribute can occur no more than once among all the dimension and auxiliary coordinates of that field.
     48  * valid for:
     49   * dimension coordinate
     50   * auxiliary coordinate
     51 * calendar
     52  * valid for:
     53   * dimension coordinate
     54   * auxiliary coordinate
     55 * leap_month
     56  * valid for:
     57   * dimension coordinate
     58   * auxiliary coordinate
     59 * leap_year
     60  * valid for:
     61   * dimension coordinate
     62   * auxiliary coordinate
     63 * month_lengths
     64  * valid for:
     65   * dimension coordinate
     66   * auxiliary coordinate
     67 * positive
     68  * valid for:
     69   * dimension coordinate
     70   * auxiliary coordinate
     71 * climatology
     72  * valid for:
     73   * dimension coordinate
     74   * auxiliary coordinate
     75
     76
     77
     78The attributes
     79 * valid_max
     80 * valid_min
     81 * valid_range
     82of data variables and coordinate variables are checks on the validity of the values, which could be verified on input and written on output. In this CF data model we assume they do not constrain any manipulations which might be done on the data in memory, and they are not part of the data model.
     83
     84The attributes
     85 * _FillValue
     86 * missing_value
     87of data variables specify how missing data is indicated in the data array. This data model supports the idea of missing data, but does not depend on any particular method of indicating it, so these attributes are not part of the model.
     88''question: is this the case for coords too, auxiliary coords may contain missing data, I believe.''
     89
     90The attributes
     91 * add_offset
     92 * compress
     93 * flag_masks
     94 * flag_meanings
     95 * flag_values
     96 * scale_factor
     97are all used in methods of compressing the data to save space in CF-netCDF files, with or without loss of information. They are not part of this data model because these operations do not logically alter the data, except that the compress attribute implies two alternative interpretations of coordinates (compressed or uncompressed).
     98
     99The featureType attribute and associated conventions provide a way of packing multiple fields of the same kind of discrete sampling geometry (timeseries, trajectories, etc.) into a single CF-netCDF data variable, in order to save space, since a multidimensional representation with common coordinate variables is typically very wasteful in such cases. This is a kind of compression. The data model regards each instance of the feature type as an independent field construct. The featureType attribute is a property of each of these field constructs.
     100
     101The attributes:
     102 * bounds
     103 * cell_measures
     104 * cell_methods
     105 * climatology
     106 * Conventions
     107 * coordinates
     108 * formula_terms
     109 * grid_mapping
     110have various special or structural functions in the CF-netCDF file format. Their functions and the relationships they indicate are reflected in the structure of this data model.  These attributes do not correspond to properties in the data model and should not be used ouside the context of CF-NetCDF.
     111
     112
     113The CF data model allows field, dimension and auxiliary coordinate constructs to have other properties not defined by CF, provided they do not conflict with CF. Since they are not part of the CF standard, the data model does not provide any interpretation of them.
     114''Question: can cell_measures, cell_methods use non-conflicting attributes?''
     115
     116
    1117=== !CellMeasure ===
    2118