Figures in appendix are not referenced correctly (or not the way I want them to :) )

In my document, I have some figures in my appendix I want to reference in my text but the output of \ref{} is only "Figure .2 shows...". It should be something like "Figure B.2".

Here's my minimal example:

\documentclass[bibliography=totoc,index=totoc,numbers=noenddot]{scrbook}
\usepackage[demo]{graphicx}
\begin{document}

\frontmatter
\include{Titel}
\tableofcontents

\mainmatter
Here is my text \ref{fig:XYZ}

\backmatter
\appendix
\renewcommand\thesection{\Alph{section}}
\chapter{Appendix}
\section{UML-Diagrams}
\begin{figure}[h]
\begin{center}
\includegraphics[width=15cm]{xyz.jpg}
\caption{\label{fig:XYZ}XYZ}
\end{center}
\end{figure}

\end{document}

-
I've added the line \usepackage[demo]{graphicx} to your MWE, as it doesn't compile otherwise. The [demo] option replaces images with black rectangles, so compilation doesn't fail because of missing images. I can't reproduce the behaviour you describe, however. I get the output Here is my text 1, and the figure caption is Figure 1: XYZ. –  Jake Oct 17 '11 at 7:06
Thank you for your editing! Wired that you get the semi-correct output?! I'd like to have it A.1 anyway. –  strauberry Oct 17 '11 at 7:10
Also please keep it a minimal working example (MWE), i.e. replace or remove the \include{Titel}. –  Martin Scharrer Oct 17 '11 at 7:21

You also need to redefine \thefigure to your own format. By default scrbook removes the chapter number from it outside the main matter. I assume now you actually want the section number in it.

Also note that you should use \centering not the center environment in floats like figure. Then {figure}[h] is never a good idea. If you don't want to make the figure float use an own environment (like center which now is OK) instead and use \captionof{figure}{...} for the caption (needs either the caption (big) or capt-of (small) package). Also, please put the \label after \caption, not inside it. It works both ways but this is better.

\documentclass[bibliography=totoc,index=totoc,numbers=noenddot]{scrbook}
\usepackage[draft]{graphicx}
\usepackage{capt-of}
\begin{document}

\mainmatter
Here is my text \ref{fig:XYZ}

Here is my text \ref{fig:XYZ2}

\backmatter
\appendix
\renewcommand\thesection{\Alph{section}}
\renewcommand{\thefigure}{\thesection.\arabic{figure}}
\chapter{Appendix}
\section{UML-Diagrams}

\begin{center}
\includegraphics[width=15cm]{xyz.jpg}
\captionof{figure}{XYZ}\label{fig:XYZ}
\end{center}

\begin{figure}
\centering
\includegraphics[width=15cm]{xyz.jpg}
\caption{XYZ2}\label{fig:XYZ2}
\end{figure}

\end{document}

-
@Jake: As always, if you know what to do you can do it. But many beginners seems to not understand the principle behind floats and try to force some Word-like behavior by default. –  Martin Scharrer Oct 17 '11 at 7:31
Okay, thank you! –  Jake Oct 17 '11 at 7:34
The renewing of the command thefigure does the job, thank you very much! A very good hint with the centering-environment, but I did not get your point :-) Could you explain it again for me? Thank you! –  strauberry Oct 17 '11 at 7:36
@strauberry: The center environment adds additional space before and after it, while the \centering macro doesn't. See Should I use center or centering for figures? for more infos. See also Label and caption without float for the other tip I mentioned. –  Martin Scharrer Oct 17 '11 at 7:45
@MartinScharrer cool thank you! I'll have a look at your links –  strauberry Oct 17 '11 at 7:51