  There exists a large field for phenomenological models in which the knowledge
of the structure of hadrons in terms of QCD constituents obtained from deep
inelastic scatterings is related to their behaviour in soft processes. One of
the simplest and oldest models is the additive quark model, with the rules of
quark statistics following from it. Originally, the relations of quark
combinatorics for hadron yields were based on the qualitative description of a
multiparticle production process as a process of the production of
non-correlated quarks and antiquarks followed by their subsequent fusion into
hadrons [20],[21]. As a large amount of new precision measurements appear, and,
on the other hand, our understanding of QCD becomes deeper, a new level of
understanding of quark-gluon physics in the region of soft interactions forces
us to review the relations of quark combinatorics. To do so, an especially good
possibility is provided by the experimental data for hadronic Z^0 decays which
allow us to check the relations of quark combinatorics for a new type of
processes: quark jets in the decays Z^0 -> q\bar{q} -> hadrons [32].
