Enforcing referential integrity for object data documents

A metadata framework helps enforce referential integrity in object data documents. In one general aspect, a method includes generating a first data definition language statement, based on a class defined in a metadata framework, that creates a table in a relational database system to store an object data document. The table may include 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. The method may also include 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.