(:
    Get a distinct collection of the authors.
    Over bibliography.xml.
    parke godfrey 2013-11-06

    One way is to use the function "distinct-values".  It takes
    a list of values in, and returns a list of values out with the
    duplicates removed.

    In doing so, the return is by value, not by reference!  This
    is because the thinking behind XQuery is that operations
    like this only make sense value-wise, not "node" wise.

    So $author is ranging over the content (values) of the
    author nodes, the text that is the authors' names.

    Note that there may be more than one node per given author
    because of repeats in the document.  If I want to retrieve
    _an_ author node per author name, I have to go back to the
    document.
:)

<portfolios>
{
    for $author in distinct-values(doc("bibliography.xml")//author/text())
    order by $author
    return (doc("bibliography.xml")//author[text() = $author])[1]
}
</portfolios>