  For a certain translation invariant tight-binding model of three-dimensional
Weyl semimetals, we establish a bulk-edge correspondence as an equality of two
relative homology classes, based on an idea of Mathai and Thiang: From spectral
information on the edge Hamiltonian, we construct a relative homology class on
the surface momentum space. This class agrees with the image under the surface
projection of a homology class on the bulk momentum space relative to the Weyl
points, constructed from the bulk Hamiltonian. Furthermore, the relative
homology class on the surface momentum space can be represented by homology
cycles whose images constitute the Fermi arc, the locus where the edge
Hamiltonian admits zero spectrum.
