The old Topology API support so called Defaults which allow to return a list of vertices which are by default in focus.

See https://github.com/opennms/opennms/blob/58a772c982e2e5485d3b5b2bdcfdb09bcc925fcc/features/topology-map/plugins/org.opennms.features.topology.plugins.topo.graphml/src/main/java/org/opennms/features/topology/plugins/topo/graphml/GraphMLTopologyProvider.java#L170 for the Topology API

The new Graph API does not have this concept, but should provide.

Acceptance Criteria

• A Default focus can be defined

• The GraphML Focus Strategies are supported:

  • A single Vertex can be defined as Default Focus

  • Nothing can be defined as Default Focus

  • All Vertices can be defined as Default Focus

  • Certain vertices can be defined as Default Focus