[thredds] Question about attributes in union aggregations

• To: THREDDS THREDDS <thredds@xxxxxxxxxxxxxxxx>
• Subject: [thredds] Question about attributes in union aggregations
• From: Gallagher James <jgallagher@xxxxxxxxxxx>
• Date: Tue, 22 Feb 2011 12:11:45 -0700

I have a union aggregation with a global attribute as well as top-level 
attributes in the two <netcdf> elements to be combined. I'm wondering about how 
these three attributes should be expressed, particularly in output from an 
opendap server. Should the response elide the second two instances of 
'Description' that appear at the top level of the <netcdf> elements? 

As you may have guessed, this is a test case from our server...

Thanks,
James

Here's the ncml:

<?xml version="1.0" encoding="UTF-8"?>
<netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2";>
        
  <!-- Test that a correct union with dimensions in the virtual datasets will 
work if the dimensions match as they need to -->
  <attribute name="title" type="string" value="Testing union with dimensions"/>

  <aggregation type="union">
    
    <netcdf>
      <attribute name="Description" type="string" value="The first dataset"/>
      <dimension name="lat" length="5"/>
      
      <!-- A variable that uses the dimension, this one will be used -->
      <variable name="Grues" type="int" shape="lat">
        <attribute name="Description" type="string">I should be in the 
output!</attribute>
        <values>1 3 5 3 1</values>
      </variable>
 
    </netcdf>
    
    <netcdf>
      <attribute name="Description" type="string" value="The second dataset"/>

      <!-- This dimension will be skipped, but the length matches the previous 
as required -->
      <dimension name="lat" length="5"/>

      <!-- This dimension is new so will be used... -->
      <dimension name="station" length="3"/>

      <!-- A variable that uses it, this one will NOT be used -->
      <variable name="Grues" type="int" shape="lat">
        <attribute name="Description" type="string">!!!! I should NOT be in the 
output! !!!!</attribute>
        <values>-3 -5 -7 -3 -1</values>
      </variable>
      
      <!-- This variable uses both and will show up in output correctly -->
      <variable name="Zorks" type="int" shape="station lat">
        <attribute name="Description" type="string">I should be in the 
output!</attribute>
        <values>
          1  2   3   4   5
          2  4   6   8  10
          4  8  12 16 20
        </values>
      </variable>
      
   </netcdf>
    
  </aggregation>

</netcdf>

--
James Gallagher
jgallagher at opendap.org
406.723.8663