In one general aspect, a method of deriving information about behavior of a target system is disclosed. The method includes accessing one or more temporal variables for the target system, providing an identifier node at the top of a hierarchy of a tree-structured belief network, and assigning a different sub-tree in the network to each of the accessed temporal variables. The method also involves accessing evidence data, and deriving information about the behavior of the target system for the evidence data based on the tree-structured belief network.