Artificial intelligence applications such as industrial robotics, military surveillance, and hazardous environment clean-up, require situation understanding based on partial, uncertain, and ambiguous or erroneous evidence. It is necessary to evaluate the relative likelihood of multiple possible hypotheses of the (current) situation faced by the decision making program. Often, the evidence and hypotheses are hierarchical in nature. In image understanding tasks, for example, evidence begins with raw imagery, from which ambiguous features are extracted which have multiple possible aggregations providing evidential support for the presence of multiple hypothesis of objects and terrain, which in turn aggregate in multiple ways to provide partial evidence for different interpretations of the ambient scene. Information fusion for military situation understanding has a similar evidence/hypothesis hierarchy from multiple sensor through message level interpretations, and also provides evidence at multiple levels of the doctrinal hierarchy of military forces.