[NOVICE] xpath query

I have a XML document which I would like to store in a table and query it using xpath function.

My document looks like this:

<ca>

<c>

<a n="color"><s>red</s></a>

<a n="year"><i>1995</i></a>

</c>

</ca>

How can I extract color. expected value is "red"

Also, is it better to dump the data into a table and then use some sort of trigger to parse it into a more normalized format for querying or is it better to to leave it as a XML dump and have the application handle the XML parsing?