About Topology Edge's sign problem

Question

I found that sign(+ or -) of edges has different meaning in different context,
such as in Edge information table, in SDO_TOPO_OBJECT (-10, 2) with SDO_TOPO_GEOMETRY constructor, etc.
What's the meaning of sign with edges in this example?
Comes from Topology and Network Data Models Developer's Guide:
-- CITY_DATA layer, land parcels (topo_geometry_ layer_id = 1),
-- parcel P2 (topo_geometry_id = 2)
SELECT SDO_TOPO.GET_TOPO_OBJECTS('CITY_DATA', 1, 2) FROM DUAL;
SDO_TOPO.GET_TOPO_OBJECTS('CITY_DATA',1,2)(TOPO_ID, TOPO_TYPE)
SDO_TOPO_OBJECT_ARRAY(SDO_TOPO_OBJECT(9, 1), SDO_TOPO_OBJECT(10, 1), SDO_TOPO_OB
JECT(13, 1), SDO_TOPO_OBJECT(14, 1), SDO_TOPO_OBJECT(17, 1), SDO_TOPO_OBJECT(18,
1), SDO_TOPO_OBJECT(6, 2), SDO_TOPO_OBJECT(7, 2), SDO_TOPO_OBJECT(8, 2), SDO_TO
PO_OBJECT(9, 2), SDO_TOPO_OBJECT(10, 2), SDO_TOPO_OBJECT(11, 2), SDO_TOPO_OBJECT
(12, 2), SDO_TOPO_OBJECT(13, 2), SDO_TOPO_OBJECT(14, 2), SDO_TOPO_OBJECT(17, 2),
SDO_TOPO_OBJECT(18, 2), SDO_TOPO_OBJECT(19, 2), SDO_TOPO_OBJECT(20, 2), SDO_TOP
O_OBJECT(-6, 2), SDO_TOPO_OBJECT(-7, 2), SDO_TOPO_OBJECT(-8, 2), SDO_TOPO_OBJECT
(-9, 2), SDO_TOPO_OBJECT(-10, 2), SDO_TOPO_OBJECT(-11, 2), SDO_TOPO_OBJECT(-12,
2), SDO_TOPO_OBJECT(-13, 2), SDO_TOPO_OBJECT(-14, 2), SDO_TOPO_OBJECT(-17, 2), S
DO_TOPO_OBJECT(-18, 2), SDO_TOPO_OBJECT(-19, 2), SDO_TOPO_OBJECT(-20, 2), SDO_TO
PO_OBJECT(-1, 3), SDO_TOPO_OBJECT(3, 3), SDO_TOPO_OBJECT(4, 3), SDO_TOPO_OBJECT(
5, 3), SDO_TOPO_OBJECT(6, 3), SDO_TOPO_OBJECT(7, 3), SDO_TOPO_OBJECT(8, 3))

Answer 1

Edges have an orientation given by the coordinates of the edge. When an edge is created in the topology, it has a certain sequence of
vertices: v1, v2, v3, ..., vn.
Now, if you want to define an road that goes from vn to v1 instead of going from v1 to vn, you define the sdo_topo_geometry
with the negative edge ID.
If you want the road to go from v1 to vn, you define the sdo_topo_geometry with the positive edge ID.
siva