Application-based vs. schema-based relationships
In RDBMS, most key fields and referential integrity are managed by the applications that use them. Multiple applications on the same database must be kept synchronised.
In ODBMS, links between objects are based on object identity which is hidden from the application. Applications need only be concerned with high-level relationships.
Notes:
As mentioned earlier, CASE tools have emerged that support the task of designing, building and managing the linkages and triggers for RDBMS entities linked through join tables. This is very important with large RDBMS applications.
CASE tools are also important for designing, understanding, and managing the relationships between entities in the user's conceptual data model. This applies to ODBMS as well as to RDBMS.
All modern design methodologies for RDBMSs are object oriented anyway, so the justification for using RDBMSs is now entirely pragmatic and not logically necessary.
OO GIS systems provide much more than a 'naked' OODBMS. In addition to spatial indexing, they provide a structure and context in which GIS operations can be done, large numbers of pre-built components and class hierarchies, and specialised tools for common GIS schema management tasks.