  Two variable flavor number schemes are used to describe bottom quark
production in deep inelastic electron-proton scattering. In these schemes the
coefficient functions are derived from mass factorization of the heavy quark
coefficient functions presented in a fixed flavor number scheme. Also one has
to construct a parton density set with five light flavors (u,d,s,c,b) out of a
set which only contains four light flavors (u,d,s,c). In order $\alpha_s^2$ the
two sets are discontinuous at $\mu=m_b$ which follows from mass factorization
of the heavy quark coefficient functions when it is carried out in the ${\bar
{\rm MS}}$-scheme. Both variable flavor number schemes give almost identical
predictions for the bottom structure functions $F_{2,b}$ and $F_{L,b}$. Also
they both agree well with the corresponding results based on fixed order
four-flavor perturbation theory over a wide range in $x$ and $Q^2$.
