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

    A second way is to use "group by".  Yes, this is quite similar to
    group by in SQL!  Again, it is value based, not node based!

    I kind of like this solution better for "distinct".  It seems cleaner,
    and the meaning is quite clear.
:)

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