I have an external process generating a XML file (every 30 secs) which is about 10MB. I would like to store the file as XML type for me to query using xpath. I plan to query it every few seconds by few hundred clients. so, it maybe easier for me create a separate table of my xpath results and have clients query that table (xpath can be expensive).
If the XML being generated has a fixed structure/schema I personally would treat the XML as a serialization format and de-serialize and store it in a database as one or more relationally linked tables. If you have to deal with the possibility of dynamic structure I would still try to put the fixed items into individual columns and then and then any dynamic items could be stuffed into an hstore typed table.
My answer to your stated question is: what happened when you tried doing that? Documentation and a bit of experimentation goes a long ways in learning.