Re: Sort list by a combination of elements

So we have <book>s with <author> elements and <book>s with a
<belongs_to> referring to a series of some author.

Problem: Sort the list of books by the author.

<xsl:sort select="concat( //book/author, //series[ @id =
current()/belongs_to/@ref ]/author )" />. This works, BUT it "feels like
a hack", if you know, what I mean.

I would prefer a more XSLT-like solution, that determines, if there is
an <author> element, sorts by this and uses the <series> author as a
fallback. Does anyone know, if and how this could be done? Schematically:

Here's the sort with:
a) by author, which can come from <series> or <book>
b) by title (all authors together, than title)

I extended the input a bit, and with the following input:
<bookshelf>
   <series id="LoTR">
       <author>Tolkien</author>
   </series>
   <book>
       <title>Two Towers</title>
       <belongs_to ref="LoTR" />
   </book>
   <book>
       <title>The hobbit</title>
       <belongs_to ref="LoTR" />
   </book>
   <book>
       <title>Pygmalion</title>
       <belongs_to ref="LoTR" />
   </book>
   <book>
       <title>It</title>
       <author>King</author>
   </book>
   <book>
       <title>Lisey's story</title>
       <author>King</author>
   </book>
   <book>
       <title>Sociology</title>
       <author>Giddens</author>
   </book>
</bookshelf>

Giddens: Sociology
King: It
King: Lisey's story
Tolkien: Pygmalion
Tolkien: The hobbit
Tolkien: Two Towers

Cheers,
-- Abel Braaksma
www.nuntia.nl