  Given a complex of groups over a finite simplicial complex in the sense of
Haefliger, we give conditions under which it is possible to build an
EZ-structure in the sense of Farrell-Lafont for its fundamental group out of
such structures for its local groups. As an application, we prove a combination
theorem that yields a procedure for getting hyperbolic groups as fundamental
groups of simple complexes of hyperbolic groups. The construction provides a
description of the Gromov boundary of such groups.
