A class of models for relaxation in strongly interacting glassy materials is suggested. Degrees of freedom are divided into a sequence of levels such that those in level n+1 are locked except when some of those in level n find the right combination to release them, this representing the hierarchy of constraints in real systems. The Kohlrausch anomalous relaxation law, exp[-(t)2], emerges naturally, and a maximum time scale is found which exhibits a Vogel-Fulcher-type temperature dependence. © 1984 The American Physical Society.