  The path-integral formulation of the hadronic tensor W_{\mu\nu} of deep
inelastic scattering is reviewed. It is shown that there are 3 gauge invariant
and topologically distinct contributions. The separation of the connected sea
partons from those of the disconnected sea can be achieved with a combination
of the global fit of the parton distribution function (PDF), the semi-inclusive
DIS data on the strange PDF and the lattice calculation of the ratio of the
strange to $u/d$ momentum fraction in the disconnected insertion. We shall
discuss numerical issues associated with lattice calculation of the hadronic
tensor involving a four-point function, such as large hadron momenta and
improved maximum entropy method to obtain the spectral density from the
hadronic tensor in Euclidean time. We also draw a comparison between the large
momentum approach to the parton distribution function (PDF) and the hadronic
tensor approach.
