  Let k be an algebraically closed field, let R be an associative k-algebra,
and let F = {M_a: a in I} be a family of orthogonal points in R-Mod such that
End_R(M_a) = k for all a in I. Then Mod(F), the minimal full sub-category of
R-Mod which contains F and is closed under extensions, is a full exact Abelian
subcategory of R-Mod and a length category in the sense of Gabriel.
  In this paper, we use iterated extensions to relate the length category
Mod(F) to noncommutative deformations of modules, and use some new methods to
study Mod(F) via iterated extensions. In particular, we give a new proof of the
characterization of uniserial length categories, which is constructive. As an
application, we give an explicit description of some categories of holonomic
and regular holonomic D-modules on curves which are uniserial length
categories.
