THREDDS Catalog Metadata

Overview

Goal

Improved THREDDS catalog responses from dynamically generated (BES) catalogs.

THREDDS catalogs typically contain metadata beyond the minimum required to simply list the catalogs holdings. This additional metadata is often comprised of Digital Library Metadata Elements. The Hyrax server is not currently able to produce THREDDS catalogs with this kind of metadata. Since these metadata elements provide crucial catalog content for dataset discovery, Hyrax needs to be improved to add this functionality.

The Problem

In a section of this THREDDS catalog: http://blackburn.whoi.edu:8081/thredds/bathy_catalog.xml we can see the Digital Library Metadata Elements:

   <dataset name="USGS Vineyard Sound Relief Model (1 arc sec)" ID="bathy/vs_1sec_20070725.nc"
            urlPath="bathy/vs_1sec_20070725.nc">
       <serviceName>Compound</serviceName>

       <authority>gov.usgs.er.whsc</authority>
       <dataType>GRID</dataType>
       <dataFormat>NetCDF</dataFormat>
       <documentation xlink:href="http://stellwagen.er.usgs.gov/models/grids/CGSherwo.doc"
                      xlink:title="USGS Vineyard Sound Coastal Relief Model (1 arc second)"/>
       <creator>
           <name vocabulary="DIF">WHSC/USGS</name>
           <contact url="http://www.usgs.gov/" email="rsignell@usgs.gov"/>
       </creator>
       <publisher>
           <name vocabulary="DIF">WHSC/USGS</name>
           <contact url="http://www.usgs.gov/" email="rsignell@usgs.gov"/>
       </publisher>
       <geospatialCoverage>
           <northsouth>
               <start>41.0</start>
               <size>1.4</size>
               <units>degrees_north</units>
           </northsouth>
           <eastwest>
               <start>-71.2</start>
               <size>0.5</size>
               <units>degrees_east</units>
           </eastwest>
           <updown>
               <start>-277.25</start>
               <size>459.6</size>
               <units>meters</units>
           </updown>
       </geospatialCoverage>

   </dataset>

A dataset element in a THREDDS catalog from Hyrax, generated from a BES showCatalog request, contains none of the Digital Library Metadata Elements:

   <dataset name="200803061600_HFRadar_USEGC_6km_rtv_SIO.ncml" ID="netcdf/examples/200803061600_HFRadar_USEGC_6km_rtv_SIO.ncml">
     <dataSize units="bytes">1162</dataSize>
     <date type="modified">2010-02-22T23:19:51</date>
     <access serviceName="dap" urlPath="netcdf/examples/200803061600_HFRadar_USEGC_6km_rtv_SIO.ncml" />
   </dataset>

However, the DDX for the dataset in question contains a significant amount of metadata. This includes DAP attributes (associated with the Unidata Dataset Discovery convention) that relate to geospatial extents:

       <Attribute name="geospatial_lat_min" type="Float32">
           <value>21.73596001</value>
       </Attribute>
       <Attribute name="geospatial_lat_max" type="Float32">
           <value>46.49441910</value>
       </Attribute>
       <Attribute name="geospatial_lon_min" type="Float32">
           <value>-97.88385010</value>
       </Attribute>
       <Attribute name="geospatial_lon_max" type="Float32">
           <value>-57.23120880</value>
       </Attribute>

How can we capitalize on this existing metadata to build THREDDS catalogs with richer metadata content?

Possible Designs

Explicit Injection and XSLT

T Path One.

   - Use NcML to place the desired metadata directly into the DDX
   - Use XSLT transforms to exctract the THREDDS namespace metadata from the DDX and add it to the THREDDS catalog response.
Explicitly into the ddx