Databases should but many don't have foreign key constraints. Does your database have them? To what extent? Here is a method to measure your database.
Overview of capabilities of commenting objects in Oracle database.
Tutorial on how to browse Dataedo database documentation directly in Oracle SQL Developer.
List of SQL queries for Oracle Data Dictionary handy for any Oracle DBA.
Short tutorial on how to quickly generate documentation for your Oracle databases with free edition of Dataedo. Part 1 of series of tutorials that show the power of Dataedo to document databases and manage database complexity.
What is Data Dictionary - explanation of its two meanings.