A time node is a zero-dimensional topological primitive that represents an identifiable node in time (it is equivalent to a point in space). A node may act as the termination or initiation of any number of time edges. A time node may be realised as a geometry, its position, whose value is a time instant.
The attribute gml:id supports provision of a handle for the XML element representing a GML Object. Its use is mandatory for all GML objects. It is of XML type ID, so is constrained to be unique in the XML document within which it occurs.
Source
<element name="TimeNode" type="gml:TimeNodeType" substitutionGroup="gml:AbstractTimeTopologyPrimitive"><annotation><documentation>A time node is a zero-dimensional topological primitive that represents an identifiable node in time (it is equivalent to a point in space). A node may act as the termination or initiation of any number of time edges. A time node may be realised as a geometry, its position, whose value is a time instant.</documentation></annotation></element>