1. A method comprising: generating a first data definition language statement, based on a class defined in a referential integrity metadata framework, that creates a table in a relational database system to store an object data document, the table including: at least one column that corresponds to an identifying attribute in the object data document, at least one column that corresponds to a relationship attribute in the object data document, and a column that stores the object data document; generating a second data definition language statement, based on the referential integrity metadata framework, that creates a foreign key constraint on the at least one column that corresponds to the relationship attribute when the relationship is not polymorphic; and issuing the first data definition language statement and the second data definition language statement to generate relational database structures that persist object data documents and relationships between object in different object data documents.