Digital Earth: GeoWeb


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The GeoWeb has a somewhat different view of georeferenced information to more traditional metadata schemes (e.g. Dublin Core, FGDC or ISO/TC211). As such, we have developed a rich metadata format for the GeoWeb based upon XML technologies, including RDF Schema. Our description allows physical objects, such as a restaurant, to be georeferenced and includes its location, a description, and links for both data (e.g. a home page, a menu, a VRML model of the building) and services (e.g. a Voice over IP address, an online takeout order form, etc.). This allows a user to search for "a South Indian restaurant with an online menu and photographs within walking distance of my hotel."

Below is a simple RDF Schema example of what a metadata record in the GeoWeb might look like.

<?xml version="1.0" encoding="utf-8"?>

<rdf:RDF
  xmlns="http://dotgeo.org/dotgeo.rdfs#"
  xmlns:gprop="http://dotgeo.org/properties.rdfs#"
  xmlns:gstr="http://geoster.com/geoster.rdfs#"
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
  xmlns:xsd="http://www.w3.org/2000/10/XMLSchema#">

  <rdf:Description>
    <location>
      <GeoLocation
        north="50.086331" east="14.413095"
        south="50.086331" west="14.413095"/>
    </location>
    <location>
      <Address city="Prague" country="Czech Republic"/>
    </location>
    <description>
      <Description xml:lang="en">
        <text> Prague castle viewed from Charles Bridge </text>
      </Description>
    </description>
    <originator>
      <Author origin="Martin Reddy"/>
    </originator>
      <link rdf:resource="http://www.ai.sri.com/~reddy/photos/cz/prague9.jpg">
        <rdf:type resource="gstr:photograph"/>
        <mimeType>image/jpeg</mimeType>
        <gstr:photoTaken> 2001-02-22 </gstr:photoTaken>
        <gprop:fileSize> 56344 </gprop:fileSize>
        <gprop:imageWidth> 705 </gprop:imageWidth>
        <gprop:imageHeight> 442 </gprop:imageHeight>
        <gprop:connection> T1 </gprop:connection>
        <copyright>
          Copyright (c) 2001 Martin Reddy. All rights reserved.
        </copyright>
      </link>
  </rdf:Description>

</rdf:RDF>

In addition to the XML schema for the GeoWeb metadata entries, we have developed schema to describe the GeoWeb infrastructure itself. This allows the actual structure to be dynamic and not hardcoded to a set hierarchy. The following schemas are important in this regard.

The GeoWeb schema file describes the structure, depth, and nature of the GeoWeb hierarchy, i.e. how many levels are in the hierarchy and the geographic extent of each cell server at each level. This will normally stay static throughout the lifetime of the GeoWeb index, but in order to allow for future expansion, or enable private GeoWeb hierarchies, the GeoWeb-enabled client always downloads the schema file first. [View Schema]
The GeoWeb hierarchy is the database of metadata items being queried. Normally, the schema file defines the nature and location of this hierarchy database. However, it is also possible to specify an explicit database, such as an XML file containing all the metadata items visible to the GeoWeb client. This is useful for putting together restricted set views onto the larger GeoWeb hierarchy, or for producing scaled-down demonstrations of the technology. [View Schema]