When XML documents are saved in a database they have to be broken down into rows and columns to be saved in the database. Also, on the other hand when the XML document is retrieved from a database the elements and attributes are recomposed to form a XML document in a text format. The process of XML marshalling and unmarshalling is handled by the DBMS. XML marshalling and XML unmarshalling can be defined as:
XML marshalling: The process of assembling individual element and attribute to a complete XML document in text format is known as XML marshalling.
XML unmarshalling: The process of breaking an XML document in to elements and attributes is known as XML unmarshalling.
For a simple XML document marshalling and unmarshalling can be done easily. However, for a complex document special mapping techniques are used. This mapping information is saved in the DBMS system catalog. Disadvantage of marshalling and unmarshalling is that it increases the processing overhead and the performance of the database is decreased.