  The phenomenological sum-rule-based approach is used to discuss the quark
composition dependence of some static and quasi-static electroweak
characteristics of nucleons.The role of nonvalence degrees of freedom, the
nucleon sea partons and/or peripheral meson currents, is shown to be important
to select and make use of the relevant symmetry parametrization of hadron
observables. With our preferable universal value of the SU(3)-symmetry
parameter $\alpha_{D}=D/F+D=.58$, taken for both magnetic moments and
axial-vector constants entering into the semi-leptonic baryon decays, we obtain
the following values for moments $\Delta q$ of the spin-dependent structure
function of the proton: $\Delta u \simeq .84(.82), \Delta d \simeq -.42(-.44),
\Delta s=-.22 \pm .05 (-.10 \pm .03)$, where the values in parentheses
correspond to the widely used "standard" value of $\alpha^{axial}_{D}=.63$. The
estimations of the strange sea contributions to the nucleon magnetic moments
and rms are also presented.
