SensorML 2.0 Examples

Metadata - Description, Name, Keywords, and Unique IDs

All SensorML 2.0 described objects are Geography Markup Language (GML) Features. The first three potential properties of any SensorML 2.0 described object are inherited from the GML schema, including gml:description, gml:identifier, and gml:name. In GML schema, these are all listed as optional; however, in SensorML 2.0, the gml:identifer property takes on a special purpose in that it provides a globally-unique identifier for the object described. As required by Schematron rules in SensorML 2.0, gml:identifier must be present and must have the codespace="UID" attribute. The value of the gml:identifier can be a unique code generated by some UID engine, or perhaps a URN that assures its uniqueness.

The other GML properties provide for an inline textual description within the gml:description property and a common name for the object described using the gml:name. For longer descriptions, GML also allows for a reference to an external description using gml:descriptionReference, although one should perhaps consider the sml:documentation property (discussed later) as a more appropriate place for referencing an external document describing the object.

Also shown here in this XML example snippet is the sml:keywords property, which as one would expect provides for a list of keywords that might assist one in discoverying this particular object (process, sensor, actuator, etc.). The sml:KeywordList element has an optional codespace attribute which can be used to reference, through a resolvable URL, a specific online dictionary or collection of terms from which these keywords can be selected.