1. A computer-implemented method for modifying an existing XML schema in a database without modifying existing data that conforms to the existing XML schema in the database, the method comprising: storing data from a set of XML documents in base database structures in a database according to an XML schema, wherein the XML schema defines an XML structure for said set of XML documents; after storing the data from the set of XML documents in the base database structures, receiving a request to make one or more changes to the schema; determining that the schema, if modified by the one or more changes, would be compatible with the stored data; and wherein the step of determining that the schema, if modified by the one or more changes, would be compatible with the stored data comprises one or more of: (a) determining that the one or more changes comprise an addition of a new element to the schema, and determining that the data stored in the base database structures in the database would be compatible with the schema as modified to add the new element; (b) determining that the one or more changes comprise a removal of an element from the schema, and determining that the data stored in the base database structures in the database would be compatible with the schema as modified to remove the element; or (c) determining that the one or more changes affect the ordering of elements within the schema, and determining that the data stored in the base database structures in the database would be compatible with the schema as modified to affect the ordering of elements within the schema; and in response to determining that the schema, if modified by the one or more changes, would be compatible with the stored data, modifying the base database structures in the database to reflect the changes to the schema without modifying the data from the set of XML documents that is stored in the base database structures; wherein the method is performed by one or more computing devices.
1. A computer-implemented method for modifying an existing XML schema in a database without modifying existing data that conforms to the existing XML schema in the database, the method comprising: storing data from a set of XML documents in base database structures in a database according to an XML schema, wherein the XML schema defines an XML structure for said set of XML documents; after storing the data from the set of XML documents in the base database structures, receiving a request to make one or more changes to the schema; determining that the schema, if modified by the one or more changes, would be compatible with the stored data; and wherein the step of determining that the schema, if modified by the one or more changes, would be compatible with the stored data comprises one or more of: (a) determining that the one or more changes comprise an addition of a new element to the schema, and determining that the data stored in the base database structures in the database would be compatible with the schema as modified to add the new element; (b) determining that the one or more changes comprise a removal of an element from the schema, and determining that the data stored in the base database structures in the database would be compatible with the schema as modified to remove the element; or (c) determining that the one or more changes affect the ordering of elements within the schema, and determining that the data stored in the base database structures in the database would be compatible with the schema as modified to affect the ordering of elements within the schema; and in response to determining that the schema, if modified by the one or more changes, would be compatible with the stored data, modifying the base database structures in the database to reflect the changes to the schema without modifying the data from the set of XML documents that is stored in the base database structures; wherein the method is performed by one or more computing devices. 2. The method of claim 1 , wherein a database structure of said base database structures includes a positional descriptor column.