As indicated previously, XML namespaces are part of National Geothermal Data System (NGDS) service-level naming conventions. Compliance with NGDS naming conventions means specifying a namespace that identifies the schema used to structure the data being deployed by the web service. An XML namespace can be provided when creating the web service:

• In an ArcGIS environment, the namespace is provided when specifying the web feature service capabilities of your web service
• In a GeoServer environment, the namespace is provided when creating a workspace

For a more detailed examination of XML and XML namespaces, see the USGIN XML Tutorial.

Table 2 contains a list of namespaces enumerated by the schemas they identify; see below for a description of each field in the table.

Table 2: XML namespaces that identify NGDS schemas; namespaces are listed by schema; entries highlighted in red represent schemas that have not yet been deployed; entries highlighted in gray represent schemas that are deprecated but remain in use

The fields in Table 2 are as follows:

• Schema and Version: The most up-to-date version of the NGDS schema used to structure the data deployed by the user; multiple versions of a given schema indicate that a transition to a newer version of that schema is in progress
• Namespace: The XML namespace that identifies the corresponding schema in the Schema and Version column
• Prefix: The XML prefix that is used to invoke the namespace later in the capabilites document of the web service deployed by the user (see below)
  • aasg indicates an AASG Geothermal Data schema
  • gsmlp indicates a GeoSciML-Portrayal schema; GeoSciML-Portrayal schemas are used for NGDS web services with line and polygon geometry (as opposed to mere points on a map); for more information, see the GeoSciML-Portrayal Cookbook

To provide a more concrete example, the capabilities document of a live web service containing data structured by the AqueousChemistry schema would appear as follows:

• In the root element of the capabilities document, the XML namespace attribute (xmlns) is used to bind the aasg prefix (which functions here as an attribute) with the corresponding namespace listed in the table above, thereby declaring the namespace, like so:

  xmlns:aasg="http://stategeothermaldata.org/uri-gin/aasg/xmlschema/aqueouschemistry/1.9"

• Having been declared as a namespace using the xmlns attribute, the aasg prefix can now be used to refer back to and invoke this namespace at any time by modifying an existing element, like so:

  <wfs:Name>aasg:WaterQuality</wfs:Name>

Here, the aasg prefix modifies the content within the Name element (itself modified by the wfs prefix, also declared in the root element of this capabilities document), thereby indicating that the content of the Name element should be interpreted within the context of the AqueousChemistry schema identified by the namespace indicated by the aasg prefix.

For help interpreting the above, the USGIN XML Tutorial is strongly recommended, particularly the section on prefixes and namespaces.

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