These are created because the database is actually managed by an ORM (object relational mapping) engine, which generates the database structure from an object model, rather than just defining the tables and columns.
This makes it quite dangerous to tamper with since things like one-to-many relationships are handled inversely.
e.g.
RDBMS
Invoice
Invoice Number
Customer ID
Total
Invoice Line
Invoice ID
Product ID
Quantity
Unit Price
Total
OODB
Invoice
ID
Invoice Number
Customer ID
Invoices Lines (list of Invoice Line IDs)
Total
Invoice Line
ID
Product ID
Quantity
Unit Price
Total