  Let (P,X) be Shimura data, M=M(P,X,K) the Shimura variety of level K. To an
algebraic representation of P, one can associate a mixed sheaf (variation of
Hodge structure, l-adic sheaf) on M. In the paper, we study the degeneration of
such sheaves along strata in toroidal compactifications of M. The main result
(2.8 in the Hodge setting, 3.9 in the l-adic setting) gives a formula for this
degeneration in terms of Hochschild cohomology of certain unipotent subgroups
of P. The new version differs from the earlier one in that the proof of 2.8 was
rewritten. In particular, the effect of Saito's specialization functor along a
stratum is identified on variations obtained via representations.
