This document provides an overview of object-relational database systems and features for supporting complex data types and object-oriented features in SQL, including: 1) Structured types allow composite attributes to be represented directly in the database with a richer type system. 2) Type inheritance in SQL allows defining subtypes that inherit attributes and methods from supertypes. 3) Collection types like arrays and multisets allow storing sets and lists of values as attributes of structured types. 4) Table inheritance maps entity-relationship subtyping to subtables in the database. 5) Methods provide procedural functionality on structured types and their instances.