9. A non-transitory computer-readable medium storing instructions which, when executed by one or more processors, cause the one or more processors to perform a method, comprising: receiving a query expression against a collection of XML documents stored in one or more database tables, wherein the collection of XML documents are stored based on a particular data storage format; determining that the query expression contains an updating expression that conforms to a language for querying XML documents, the updating expression specifying particular operation for updating XML data; in response to determining that the query expression contains the updating expression that conforms to the language for querying XML documents, rewriting the query expression to form a first rewritten query expression comprising one or more path-based query operators, wherein the one or more path-based query operators are selected based on the particular operation for updating XML data specified by the updating expression; based on the particular data storage format storing the collection of XML documents, rewriting the first rewritten query expression to form a second rewritten query expression comprising one or more storage format specific query operators configured to update particular XML data of the collection of XML documents.
9. A non-transitory computer-readable medium storing instructions which, when executed by one or more processors, cause the one or more processors to perform a method, comprising: receiving a query expression against a collection of XML documents stored in one or more database tables, wherein the collection of XML documents are stored based on a particular data storage format; determining that the query expression contains an updating expression that conforms to a language for querying XML documents, the updating expression specifying particular operation for updating XML data; in response to determining that the query expression contains the updating expression that conforms to the language for querying XML documents, rewriting the query expression to form a first rewritten query expression comprising one or more path-based query operators, wherein the one or more path-based query operators are selected based on the particular operation for updating XML data specified by the updating expression; based on the particular data storage format storing the collection of XML documents, rewriting the first rewritten query expression to form a second rewritten query expression comprising one or more storage format specific query operators configured to update particular XML data of the collection of XML documents. 14. The non-transitory computer-readable medium of claim 9 , wherein the first rewritten query expression further comprises a SQL conditional statement based on a conditional expression identified in the updating expression.