Question: Are there disadvantages of using XML, instead of RDMS? The reason I ask this is because my data is more naturally represented by XML structure, rather than RDBMS. I initially thought of [storing the data in relational database](https://stackoverflow.com/questions/545145/map-xml-structure-to-database-schema), but the lack of flexibility of relational database to handle tree-like data structure was putting me of. So I am thinking about just storing the data in XML.

One thing I fear is performance penalty. While RDBMS can handle large datasets, I am not sure whether the same can be said about XML. Also, the database queries are pretty well-established and fairly easy to use and construct, what about XML queries? I don't know.

I am doing .Net application.

Answer: 
In my opinion, these are the factors to consider

1. Which fits your applications needs more closely
2. How large a data set you need to handle?
3. Are you transferring data between applications or are you going to query it?

Once these factors are considered, I would suggest that you decide to use RDBMS, if you have large data processing and querying needs and XML if you need to export data or transfer it between applications. i would also like to suggest that you consider constraints on your data and integrity needs like Nick has suggested.

I have little experience in the area, however this is what I have heard from others at my school.

All the best.
You should not compare XML with an RDBMS, since that are 2 complementary technologies; XML should not be considered, or regarded as a replacement for an RDMBS.

An RDMBS is for storing large amounts of data in a consistent way. The RDBMS should take care of the consistentcy of the data, etc ...

XML can be used for data-exchange between different computer systems for instance, but it should not be used to store large amounts of data over a long period of time.  

Xml doesn't allow you to take care of data-consistency like an RDMBS does; it doesn't take care of transactions, etc... Xml is actually nothing more then a text-file, that contains data in some kind of structured way.