In addition to extract or read/write support on single table with spatial tables, OpenCities Map supports the concept of storing annotations in Oracle. This requires a separate spatial table that is related to the table with the parent feature in it. Adding an annotation table is a three step process:

• First, a spatial table is created, including the right metadata entry and spatial index;

• Second, a composite primary key is added to the table;

• Finally, a foreign key is added to ‘formalize’ the relationship between the annotation table and the parent table.