DAP Design: shared dimensions, groups and types

Back: DAP3/4#NC-DAP

Shared Dimensions

Shared dimensions will be added to DAP so that special variables used to identify the independent parameters in non-scalar variables can be clearly labeled as such. When a dimension is named, each use of that dimension means the same values. Each dimension will have both a name and a size in addition to a type. The moniker Shared Dimension is really redundant. Any Dimension in DAP 3.3 can be shared. There is no requirement that a dimension be used; it can be declared and never used.

Dimension examples

Declaring dimensions in the DDX:

<Dataset name="dimension_ex_1" ...>
    <!-- The 'dimensions' section must come first if present -->
    <dimensions>
        <!-- Dimensions are declared like an array except that the 
             'dimension' element is replaced by an 'extent' element
             and the extent has no name (since the dimension itself
             is named -->
        <Int32 name="latitude">
            <extent size="1024">
        </Int32>
        <String name="color">
            <extent size="3">
        </String>
    </dimensions>

    <!-- remainder of the document -->

</Dataset>

Using dimensions in the DDX. In DAP, dimensions can only be used in a Grid variable;

<Dataset name="dimension_ex_1" ...>
    <dimensions>
        <Int32 name="latitude">
            <dimension size="1024">
        </Int32>
        <Int32 name="longitude">
            <dimension size="1024">
        </Int32>
    </dimensions>

    <!-- The two declarations that follow are effectively Grids,
         but now share the same dimentions -->
    <Byte name="uwnd">
        <!-- note that only the name is used, not the size -->
        <map name="latitude">
        <map name="longitude">
    </Byte>

    <Byte name="vwnd">
        <map name="latitude">
        <map name="longitude">
    </Byte>

    ...

</Dataset>