  In this paper, we investigate some chemokinematical properties of the Milky
Way disk, by using a sample composed by 424 late-type dwarfs. We show that the
velocity dispersion of a stellar group correlates with the age of this group,
according to a law proportional to t^0.26, where t is the age of the stellar
group. The temporal evolution of the vertex deviation is considered in detail.
It is shown that the vertex deviation does not seem to depend strongly on the
age of the stellar group. Previous studies in the literature seem to not have
found it due to the use of statistical ages for stellar groups, rather than
individual ages. The possibility to use the orbital parameters of a star to
derive information about its birthplace is investigated, and we show that the
mean galactocentric radius is likely to be the most reliable stellar birthplace
indicator. However, this information cannot be presently used to derive radial
evolutionary constraints, due to an intrinsic bias present in all samples
constructed from nearby stars. An extensive discussion of the secular and
stochastic heating mechanisms commonly invoked to explain the age-velocity
dispersion relation is presented. We suggest that the age-velocity dispersion
relation could reflect the gradual decrease in the turbulent velocity
dispersion from which disk stars form, a suggestion originally made by Tinsley
and Larson (1978) and supported by several more recent disk evolution
calculations. A test to distinguish between the two types of models using
high-redshift galaxies is proposed.
