Tree structures that use logic gates to model system behavior have proven very useful in safety and reliability studies. In particular process trees are the basic structure used in a decision analysis methodology developed at Los Alamos called Logic Evolved Decision modeling (LED). LED TOOLS is the initial attempt to provide LED-based decision analysis tools in a state of the art software package. The initial release of the software, Version 2.0, addresses the first step in LED — determination of the possibilities. LED TOOLS is an object-oriented application written in Visual Basic for Windows NT based operating systems. It provides an innovative graphical user interface that was designed to emphasize the visual characteristics of logic trees and to make their development efficient and accessible to the subject matter experts who possess the detailed knowledge incorporated in the process trees. This eliminates the need for the current interface between subject matter experts and logic modeling experts. This paper provides an introduction to LED TOOLS. We begin with a description of the programming environment. The construction of a process tree is described and the simplicity and efficiency of the approach incorporated in the software is discussed. We consider the nature of the logical equations that the tree represents and show how solution of the equations yield natural language “paths.” Finally we discuss the planned improvements to the software.

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