The DOM provides a rich set of functions that you can use to interpret and manipulate an XML document, but those functions come at a price. As the original DOM for XML documents was being developed, a number of people on the XML-DEV mailing list voiced concerns about it:

• The DOM builds an in-memory tree of an entire document. If the document is very large, this requires a significant amount of memory.
• The DOM creates objects that represent everything in the original document, including elements, text, attributes, and whitespace. If you only care about a small portion of the original document, it's extremely wasteful to create all those objects that will never be used.
• A DOM parser has to read the entire document before your code gets control. For very large documents, this could cause a significant delay.

These are merely issues raised by the design of the Document Object Model; despite these concerns, the DOM API is a very useful way to parse XML documents.