Databases Reference
In-Depth Information
(WCS) as well as Web Image Classification service and Web Coordinate Trans-
formation Services. These Web services allow the access of OGC compliant
data services around the globe with geographic region, temporal and thematic
specifications. In addition, these Web can be dynamically composed together
to produce value-added data products.
The OpenGIS Catalog Service for Web (CSW) [21] is a standard support-
ing the registry and discovery of geospatial data, where data providers register
their capabilities using metadata that can be used for service discovery by the
users. Some of the catalog services include ”getCapabilities”, ”DescribeRe-
cord”, ”GetDomain”, ”GetRecords”, ”GetRecordbyID”, etc. Web Coverage
Services include ”getCapabilities”, ”describeCoverage” and ”getCoverage”.
For instance, ”describeCoverage” will provide information of an image data
such as bounding box, resolution and spatial reference system. Web Feature
Services support ”getFeatureType”, ”getFeature”, ”getGmlObject” and ”get-
Capabilities” to access and interchange the vector data that is a set of at-
tributes, represented with (name, type and value) tuples where one attribute
has a geometry as its value. Web Map Services include ”getMap”, ”getFea-
tureInfo” or ”getCapabilities”. For instance, ”getMap” service supports the
map as images in PNG, JPG or GIF format, that can be layered.
The following example shows the ”GetGmlObject” request for the name
of a town whose identifier is ”t1” with traversing to the second level of the
nested XLink:
<?xml version="1.0" encoding="UTF-8"?>
<wfs:GetGmlObject
xmlns:wfs="http://www.opengis.net/wfs"
xmlns:ogc="http://www.opengis.net/ogc"
xmlns:gml="http://www.opengis.net/gml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opengis.net/wfs ../wfs/1.1.0/WFS.xsd"
service="WFS"
version="1.1.0"
outputFormat=" text/xml; subtype=gml/3.1.1"
traverseXlinkDepth="*"
traverseXlinkExpiry="2">
<ogc:GmlObjectId gml:id="t1"/>
</wfs:GetGmlObject>
The query response contains one result with the town name ”West Orange”
that is directed to a point feature ”townhall” located in a particular position,
as shown in the following.
<Town gml:id="t1">
<gml:name>West Orange</gml:name>
<gml:directedNode orientation="+"> <!-- xlink:href="#n1" ..
<gml:Node gml:id=n1>
<gml:pointProperty xlink:href="http://www.westorgane.nj.us/
/gps.gml#townHall/">
<gml:Point gml:id="townHall">
<gml:pos>147 234</gml:pos>
</gml:Point>
</gml:pointProperty>
</gml:Node>
</gml:directedNode>
</Town>
