  This paper deals with the design of Excitation and Measurement Patterns (EMP)
for the identification of a class of dynamical networks whose topology has the
structure of a Directed Acyclic Graph (DAG). In addition to the by now well
known condition that the identifiabiltiy of any dynamical network requires that
the sources be excited, the sinks be measured, and all other nodes be either
excited or measured, we show that for DAGs two other types of nodes have
special excitation and measurement requirements. Armed with this result, we
propose a systematic procedure for the design of EMPs that guarantee
identifiability of a network with DAG topology.
