Adapting the theory of the derived category to ordered groupoids, we prove
that every ordered functor (and thus every inverse and regular semigroup ho
momorphism) factors as an enlargement followed by an ordered fibration. As
an application, we obtain Lawson's version of Ehresmann's Maximum Enlargeme
nt Theorem, from which can be deduced the classical theory of idempotent-pu
re inverse semigroup homomorphisms and E-unitary inverse semigroups.