This master's thesis has been done in the Laboratory of Computer and Information Science in the Helsinki University of Technology in cooperation with the Jaakko Pöyry Consulting.

I'd like to thank my instructor Petri Vasara and my supervisor professor Olli Simula for their guidance and for making this work possible. I would also like to thank my collegues in the laboratory for their invaluable advice and help during this work. Special thanks to Esa Alhoniemi for many enlightning discussions, to Sami Kaski for his valuable comments and to Lea Leinonen for the evening tea breaks without which scientific progress would surely come to a halt.

Most of all I'd like to thank my wonderful wife Riikka for helping and supporting me with this work and life in general. There's no one like you.

In Otaniemi May 26, 1997

Juha Vesanto

Don't worry about the world coming to an end today.
It's already tomorrow in Australia.

- Charles Schultz

Juha Vesanto
Tue May 27 12:40:37 EET DST 1997