DAP4 Attribute Model: Difference between revisions

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=== Background ===
=== Background ===


 
In order to create a more flexible metadata channel for the DAP we will add a new type of Attribute object the DAP Attribute data model. This new Attribute type, called ''xml'', will be allowed to contain any XML from a non DAP namespace. For example, XML content from the GML or WCS namespaces could be included here. Even an Open Office document describing the content would be legal.


== Re-factoring the representation of DAP Attribute objects. ==
== Re-factoring the representation of DAP Attribute objects. ==

Revision as of 04:03, 22 January 2009

Add a DAP Attribute with type xml.

Goal

Provide a mechanism for including any XML markup from namespaces other than the DAP namespaces as metadata associated with any DAP variable.

Background

In order to create a more flexible metadata channel for the DAP we will add a new type of Attribute object the DAP Attribute data model. This new Attribute type, called xml, will be allowed to contain any XML from a non DAP namespace. For example, XML content from the GML or WCS namespaces could be included here. Even an Open Office document describing the content would be legal.

Re-factoring the representation of DAP Attribute objects.

Goals

Provide an improved XML representation of the DAP Attributes.

Background

The original DDX represented Attribute objects as a single XML element dap:Attribute. The type of the DAP Attribute was represented as the value of an XML attribute names type. For example: 

   <Attribute name="bears" type="Container">
       <Attribute name="act" type="String">
           <value>text string\\012\\011123</value>
       </Attribute>
       <Attribute name="acs" type="Int16">
           <value>-40</value>
       </Attribute>
   </Attribute>

This is unlike the scheme for variables in which each one is represented by an XML element whose name reflects the type of the variable: 

       <String name="satellite"/>
       <Int32 name="year"/>

A more parallel representation can be achieved by creating a separate namespace for the DAP Attribute data model. This way the two representations can more closely resemble each other, and they can be easily filtered and manipulated using namespace aware processing (which really is a key component of the XML use model).

Design

Each type of DAP Attribute type will have its own XML element representation in the DAP Attribute namespace: http://xml.opendap.org/ns/DAP/3.3/att#

  • xmlns:att="http://xml.opendap.org/ns/DAP/3.3/att#" Using the att prefix to identify the DAP Attribute namespace.
  • <att:Byte /> - Represents a byte valued Attribute.
  • <att:Int16 /> - Represents a 16 bit integer valued Attribute.
  • <att:UInt16 /> - Represents an unsigned 16 bit integer valued Attribute.
  • <att:Int32 /> - Represents a 32 bit integer valued Attribute.
  • <att:UInt32 /> - Represents an unsigned 32 bit integer valued Attribute.
  • <att:Float32 /> - v a 32 bit floating point valued Attribute.
  • <att:Float64 /> - Represents a 64 bit floating point valued Attribute.
  • <att:String /> - Represents a String valued Attribute.
  • <att:URL /> - Represents a URL valued Attribute.
  • <att:Container /> - Represents a Container Attribute.
  • <att:XML /> - Represents an Attribute object that may hold any XML not in the DAP namespaces and identifies it as an Attribute. (Assuming we want to wrap foreign XML in an Attribute tag)

Schema

Here is the prototype schema for the DAP4 namespace

  • Simpler due to moving the DAP Attributes to their own schema.

Here is the prototype schema for the DAP4 Attribute namespace

  • Needs a few changes/corrections:
  1. The AttributeUrlType Allows the URL type to contain any URI. We need to modifiy the schema so that it it is restricted to any URL. Or we might wish to relax the DAP definition of the URL Attribute type to become a URI.
  2. The AttributeXMLType - Allows any XML not in the DAP Attribute namespace. We should try to make this any XML not in the DAP or the DAP Attribute namespaces (IE: XML not in http://xml.opendap.org/ns/DAP/3.3/att# or http://xml.opendap.org/ns/DAP/3.3/dap#)

Source XML

<?xml version="1.0" encoding="UTF-8"?>
<Dataset name="200803061600_HFRadar_USEGC_6km_rtv_SIO.nc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xml.opendap.org/ns/DAP2"
xsi:schemaLocation="http://xml.opendap.org/ns/DAP2  http://xml.opendap.org/dap/dap2.xsd">



  <Attribute name="wcsStuff" type="xml" >
    <CoverageDescription xmlns="http://www.opengis.net/wcs/1.1" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:owcs="http://www.opengis.net/wcs/1.1/ows" xmlns:gml="http://www.opengis.net/gml/3.2" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:schemaLocation="http://www.opengis.net/wcs/1.1  http://schemas.opengis.net/wcs/1.1.0/wcsDescribeCoverage.xsd  http://www.opengis.net/ows/1.1  http://schemas.opengis.net/ows/1.1.0/owsAll.xsd  http://www.opengis.net/wcs/1.1/ows http://schemas.opengis.net/wcs/1.1.0/owsDataIdentification.xsd http://www.opengis.net/gml/3.2  http://schemas.opengis.net/gml/3.2.1/gml.xsd">
        <ows:Title>Near-Real Time Surface Ocean Velocity</ows:Title>
        <ows:Abstract>CoverageDescription generated by OPeNDAP WCS UseCase 2.0</ows:Abstract>
        <Identifier>coverage/200803061600_HFRadar_USEGC_6km_rtv_SIO.nc</Identifier>
        <Domain>
            <SpatialDomain>
                <ows:BoundingBox crs="urn:ogc:def:crs:EPSG::4326">
                    <ows:LowerCorner>-97.8839 21.736</ows:LowerCorner>
                    <ows:UpperCorner>-57.2312 46.4944</ows:UpperCorner>
                </ows:BoundingBox>
            </SpatialDomain>
            <TemporalDomain>
                <gml:timePosition>2008-03-27T16:00:00.000Z</gml:timePosition>
            </TemporalDomain>
        </Domain>
        <Range>
        </Range>
        <SupportedCRS>urn:ogc:def:crs:EPSG::4326</SupportedCRS>
        <SupportedFormat>netcdf-cf1.0</SupportedFormat>
        <SupportedFormat>dap2.0</SupportedFormat>
    </CoverageDescription>

    <CoverageSummary xmlns="http://www.opengis.net/wcs/1.1" xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:owcs="http://www.opengis.net/wcs/1.1/ows" xmlns:gml="http://www.opengis.net/gml/3.2" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:schemaLocation="http://www.opengis.net/wcs/1.1  http://schemas.opengis.net/wcs/1.1.0/wcsDescribeCoverage.xsd  http://www.opengis.net/ows/1.1  http://schemas.opengis.net/ows/1.1.0/owsAll.xsd  http://www.opengis.net/wcs/1.1/ows http://schemas.opengis.net/wcs/1.1.0/owsDataIdentification.xsd http://www.opengis.net/gml/3.2  http://schemas.opengis.net/gml/3.2.1/gml.xsd">
       <ows:Title>6km HF Radar data</ows:Title>
       <ows:Abstract>A test dataset for use developing WCS services.</ows:Abstract>
       <ows:Metadata xlink:href="http://ndp.opendap:8080/opendap/coverage/200803061600_HFRadar_USEGC_6km_rtv_SIO.nc.das"/>
       <ows:WGS84BoundingBox>
          <ows:LowerCorner>-97.8839 21.736</ows:LowerCorner>
          <ows:UpperCorner>-57.2312 46.4944</ows:UpperCorner>
       </ows:WGS84BoundingBox>
       <Identifier>coverage/200803061600_HFRadar_USEGC_6km_rtv_SIO.nc</Identifier>
    </CoverageSummary>
  </Attribute>

    <Attribute name="NC_GLOBAL" type="Container">
        <Attribute name="title" type="String">
            <value>Near-Real Time Surface Ocean Velocity</value>
        </Attribute>
        <Attribute name="institution" type="String">
            <value>Scripps Institution of Oceanography</value>
        </Attribute>
        <Attribute name="source" type="String">
            <value>Surface Ocean HF-Radar</value>
        </Attribute>
        <Attribute name="history" type="String">
            <value>12-Mar-2008 22:26:19:  NetCDF file created</value>
        </Attribute>
        <Attribute name="references" type="String">
            <value>Terrill, E. et al., 2006. Data Management and Real-time\\012Distribution in the HF-Radar National Network. Proceedings\\012of the MTS/IEEE Oceans 2006 Conference, Boston MA,\\012September 2006.</value>
        </Attribute>
    </Attribute>

    <Grid name="u">
      <Attribute name="wcsStuff" type="xml" >
        <Field>
            <ows:Title>surface_eastward_sea_water_velocity</ows:Title>
            <ows:Abstract>Eastward component of a 2D sea surface velocity vector.</ows:Abstract>
            <Identifier>u</Identifier>
            <Definition>
                <ows:AnyValue/>
            </Definition>
            <NullValue>-32768</NullValue>
            <owcs:InterpolationMethods>
                <owcs:DefaultMethod>nearest</owcs:DefaultMethod>
            </owcs:InterpolationMethods>
        </Field>
      </Attribute>
        <Attribute name="standard_name" type="String">
            <value>surface_eastward_sea_water_velocity</value>
        </Attribute>
        <Attribute name="units" type="String">
            <value>m s-1</value>
        </Attribute>
        <Attribute name="_FillValue" type="Int16">
            <value>-32768</value>
        </Attribute>
        <Attribute name="scale_factor" type="Float32">
            <value>0.009999999776</value>
        </Attribute>
        <Attribute name="ancillary_variables" type="String">
            <value>DOPx</value>
        </Attribute>
        <Array name="u">
            <Int16/>
            <dimension name="time" size="1"/>
            <dimension name="lat" size="460"/>
            <dimension name="lon" size="701"/>
        </Array>
        <Map name="time">
            <Int32/>
            <dimension name="time" size="1"/>
        </Map>
        <Map name="lat">
            <Float32/>
            <dimension name="lat" size="460"/>
        </Map>
        <Map name="lon">
            <Float32/>
            <dimension name="lon" size="701"/>
        </Map>
    </Grid>

    <dataBLOB href=""/>
</Dataset>
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