xml and query languages

Can someone explain why there are so many query langages for xml files ?
xql, xpath, xpointer, xml-ql, xquery ... :o(
What's the reason of this non-unicity ?
What are the relationships between all this solutions ?
What are the most important recommandations we have to follow in the future
?
They are so numerous and they seem to be very close, the interactions and
the dependencies are too dark for me.....

Thanks

Y.G.