Extending fault trees with an AND-THEN gate

Fault trees have been used for software safety analysis in various safety critical systems. The PRIORITY-AND gate was proposed because the conventional AND gate cannot be used to represent the sequential order of the events. The paper shows that even PRIORITY-AND gate is not expressive enough to represent the relative temporal order of the events precisely. We extend the fault trees with an AND-THEN gate that is the corresponding gate of the logical connective TAND. This increases the expressive power of the fault trees. The AND-THEN gate can represent relative temporal relations precisely.