gml:Edge 

gml:Edge represents the 1-dimensional primitive.
The topological boundary of an Edge (gml:directedNode) consists of a negatively directed start Node and a positively directed end Node.   
The optional coboundary of an edge (gml:directedFace) is a circular sequence of directed faces which are incident on this edge in document order. In the 2D case, the orientation of the face on the left of the edge is "+"; the orientation of the face on the right on its right is "-". 
If provided, the aggregationType attribute shall have the value "sequence".
An edge may optionally be realised by a 1-dimensional geometric primitive (gml:curveProperty).

Element Information

Model

gml:metaDataProperty* , gml:description{0,1} , gml:descriptionReference{0,1} , gml:identifier{0,1} , gml:name* , gml:container{0,1} , gml:directedNode{2,2} , gml:directedFace* , gml:curveProperty{0,1}
Children: gml:container, gml:curveProperty, gml:description, gml:descriptionReference, gml:directedFace, gml:directedNode, gml:identifier, gml:metaDataProperty, gml:name

Attributes

QName Type Fixed Default Use Inheritable Annotation
aggregationType gml:AggregationType optional
gml:id ID required 
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.

Used By

Complex Types gml:DirectedEdgePropertyType, gml:NodeOrEdgePropertyType

Source 

<element name="Edge" type="gml:EdgeType" substitutionGroup="gml:AbstractTopoPrimitive">
  <annotation>
    <documentation>gml:Edge represents the 1-dimensional primitive. The topological boundary of an Edge (gml:directedNode) consists of a negatively directed start Node and a positively directed end Node. The optional coboundary of an edge (gml:directedFace) is a circular sequence of directed faces which are incident on this edge in document order. In the 2D case, the orientation of the face on the left of the edge is "+"; the orientation of the face on the right on its right is "-". If provided, the aggregationType attribute shall have the value "sequence". An edge may optionally be realised by a 1-dimensional geometric primitive (gml:curveProperty).</documentation>
  </annotation>
</element>

Sample