1. A method comprising: providing an entity-relationship (ER)-extensible markup language (XML) hybrid data model comprising at least one unmarked entity and at least one entity marked to be transformed as an XML column; and transforming, by a computing processor, the ER-XML hybrid data model to a physical data model, comprising: transforming the at least one unmarked entity to a table in the physical data model; determining whether the at least one marked entity has an unmarked parent entity; and in response to determining that the at least one marked entity has the unmarked parent entity: transforming the at least one marked entity and a transitive closure of the at least one marked entity to an XML column in a table representing the unmarked parent entity in the physical data model; generating an XML schema document (XSD) for the XML column; and associating the XSD with the XML column.