Topology: basic DB layout

ISO layout for DB tables implementing a Topology-Geometry

Accordingly to ISO/IEC 13249-3 (SQL/MM) specifications a Topology-Geometry should be implemented as a set of three strictly related DB tables respectively intended for Nodes, Edges and Faces.
The ISO standard dictates that several unrelated Topologies can safely coexist into the same DBMS instance, each one of them being stored on its own separate SCHEMA identified by the same name of the individual Topology.
SQLite has no equivalent concept of SCHEMA, so SpatiaLite's own Topologies will be implemented as a set of tables sharing the same name-prefix.

<topology>_NODE
NODE_ID	INTEGER	Node unique identifier.
CONTAINING_FACE	INTEGER	Unique identifier of the Face containing the Node. Only *isolated Nodes* may be contained within a Face; non-isolated Nodes must declare a NULL value.
GEOMETRY	POINT	Location of the Node.

<topology>_EDGE
EDGE_ID	INTEGER	Edge unique identifier.
START_NODE	INTEGER	Unique identifier of the Node at the start of the Edge.
END_NODE	INTEGER	Unique identifier of the Node at the end of the Edge.
LEFT_FACE	INTEGER	Unique identifier of the Face on the left side of the Edge when looking in the direction from START_NODE to END_NODE.
RIGHT_FACE	INTEGER	Unique identifier of the Face on the right side of the Edge when looking in the direction from START_NODE to END_NODE All *isolated Edges* have the same Face both on the left and right sides.
NEXT_LEFT_EDGE	INTEGER	Unique identifier of the next Edge of the Face on the left (when looking in the direction from START_NODE to END_NODE), moving counterclockwise around the Face boundary.
NEXT_RIGHT_EDGE	INTEGER	Unique identifier of the next Edge of the Face on the right (when looking in the direction from START_NODE to END_NODE), moving counterclockwise around the Face boundary.
GEOMETRY	CURVE	Geometry of the Edge. The first vertex of the Edge must exactly match START_NODE and the last vertex must match END_NODE.

<topology>_FACE
FACE_ID	INTEGER	Face unique identifier. Every Topology-Geometry is always expected to declare the Universal Face identified by an ID value 0 (zero).
MBR	RECTANGLE	Minimum bounding box (aka BBOX) of the Face. The Universal Face is expected to declare a NULL MBR because the Universal Face can never be represented as a geometry.

ISO layout for DB tables implementing a Topology-Network

ISO Topology-Network adopts a slightly different layout; in this case there are simply two DB tables respectively intended for Nodes and Links.
Different Networks can coexist within the same database, and will be implemented as a set of tables sharing the same name-prefix.

<network>_NODE
NODE_ID	INTEGER	Node unique identifier.
GEOMETRY	POINT	Location of the Node. All Nodes in a Logical Network must declare a NULL geometry.

<network>_LINK
LINK_ID	INTEGER	Link unique identifier.
START_NODE	INTEGER	Unique identifier of the Node at the start of the Link.
END_NODE	INTEGER	Unique identifier of the Node at the end of the Link.
GEOMETRY	CURVE	Geometry of the Link. The first vertex of the Link must exactly match START_NODE and the last vertex must match END_NODE. All Links in a Logical Network must declare a NULL geometry.

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