  We present a coherent theoretical study of ultrarelativistic heavy-ion data
obtained at the CERN/SPS by the NA35/NA49 Collaborations using 3+1-dimensional
relativistic hydrodynamics. We find excellent agreement with the rapidity
spectra of negative hadrons and protons and with the correlation measurements
in two experiments: $S+S$ at 200 $AGeV$ and $Pb+Pb$ at 160 $AGeV$ (preliminary
results). Within our model this implies that for $Pb+Pb$ ($S+S$) a
quark-gluon-plasma of initial volume 174 $fm^3$ (24 $fm^3$) with a lifetime 3.4
$fm/c$ (1.5 $fm/c$) was formed. It is found that the Bose-Einstein correlation
measurements do not determine the maximal effective radii of the hadron sources
because of the large contributions from resonance decay at small momenta. Also
within this study we present an NA49 acceptance corrected two-pion
Bose-Einstein correlation function in the invariant variable, $Q_{inv}$.
