A system and a method for synchronizing and updating a relational database with supplemental data in which the relational database has a set of tables defined by a relational schema. The supplemental data preferably comprises data in a tagged format having a document-type definition representative of the relational schema and is represented in a document object. The system and method preferably ensure record-by-record updating and synchronization of the relational database with the at least one proposed data update by receiving at least one proposed data update from a source external to the relational database; and propagating the received at least one proposed data update into the relational database. In this matter, the compliance with both the relational database relational schema and the tagged data document type definition is ensured without requiring reloading existing data in the relational database.