This article has a few typos.  It says:

The next line describes the root element of the document (like it was saying: "this document is a article") i.e., “ARTICLE”.

The next lines describe the child elements of the root (TITLE, DATE, AUTHOR, SUMMARY, and CONTENT).

Each element can also have child’s i.e. AUTHOR has FNAME and LNAME.

But the example XML file has a root of “ARTICLES”.  There is one child “ARTICLE” in the root and then the next lines decribe child elements of the “ARTICLE” element.

In the XPATH example it says:

ARTICLE[DATE = "05/16/2005"]     - All <DATE> elements which has at least one <DATE> child-element child with the value "05/16/2005".

Should say ARTICLE[DATE = "05/16/2005"]     - All <ARTICLE> elements...

Since this article is directed towards SQL people, a big point to make is that elements are case sensitive.

<ARTICLE>This is NOT XML and will not be accepted as well formed.</Article>