@article{ref1,
title="Introducing the X-tree",
journal="Hazard prevention: journal of system safety",
year="2007",
author="Benner, Ludwig and Rimson, Ira J.",
volume="43",
number="2",
pages="4-7",
abstract="At what point have we lowered the probability of an event enough?  <p>Language Eng</p>",
language="",
issn="0743-8826",
doi="",
url="http://dx.doi.org/"
}