When to Use the DOM
Because the DOM represents an XML document as a tree in memory, it is best used for small documents or documents for which the memory footprint is known in advance, and when the application needs to manipulate the document’s structure rather than just reading in the XML data.
One thing to keep in mind if you are considering using the DOM is
that the entire document must be read into memory before any of it is
available for use. This differs from the read-only, forward-only
XmlReader, which allows you to read a
single node at a time, and thus gives you the ability to deal with
very large XML documents efficiently.
For this reason, the DOM is also appropriate when you need to access XML elements or attributes non-sequentially. The entire document is resident in memory, so searching for a particular node does not require disk access.