Most enterprise data today is stored in relational databases. Based on the relational data model developed in 1970 by E. F. Codd, relational databases store data in a collection of tables. Columns in each table represent the data's attributes, and rows represent individual records. Keys link records together, both within the same table and across tables. The Structured Query Language (SQL) operates on the stored data.
JDO / Relational, or JDOR for short, is a subset of the JDO specification dedicated to relational databases. JDOR standardizes how to map objects to relational tables, how to perform queries in SQL rather than JDOQL, and how to interact with database sequences. The remainder of this document covers each of these topics in detail.