what is a mature api / solution for this problem ?
1. user always submit XML document from page, the server side need to save this xml data to sql database.
2. user could add/delete field (node) in the Runtime, server side should detect this modification and make change on sql database accordingly.
for example, user add a new field "age", then it should add a new column in database and save this "age" data into database.
3. when retrieving data from database, it will generate xml file base on table metadata .