  The discrete non-linear Schrodinger (NLS) model in the presence of an
integrable defect is examined. The problem is viewed from a purely algebraic
point of view, starting from the fundamental algebraic relations that rule the
model. The first charges in involution are explicitly constructed, as well as
the corresponding Lax pairs. These lead to sets of difference equations, which
include particular terms corresponding to the impurity point. A first glimpse
regarding the corresponding continuum limit is also provided.
