  Based on some important properties of $dS$ space, we present a Beltrami model
${\cal B}_\Lambda$ that may shed light on the observable puzzle of $dS$ space
and the paradox between the special relativity principle and cosmological
principle. In ${\cal B}_\Lambda$, there are inertial-type coordinates and
inertial-type observers. Thus, the classical observables can be defined for
test particles and light signals. In addition, by choosing the definition of
simultaneity the Beltrami metric is transformed to the Robertson-Walker-like
metric. It is of positive spatial curvature of order $\Lambda$. This is more or
less indicated already by the CMB power spectrum from WMAP and should be
further confirmed by its data in large scale.
