The characteristic sequence of hypergraphs $<P_n : n<\omega>$ associated to a
formula $\phi(x;y)$, introduced in [arXiv:0908.4111], is defined by
$P_n(y_1,... y_n) = (\exists x) \bigwedge_{i\leq n} \phi(x;y_i)$. This paper
continues the study of characteristic sequences, showing that graph-theoretic
techniques, notably Szemer\'edi's celebrated regularity lemma, can be naturally
applied to the study of model-theoretic complexity via the characteristic
sequence.
For a first-order formula $\phi(x;y)$ we introduce and study the
characteristic sequence $<P_n : n < \omega>$ of hypergraphs defined by
$P_n(y_1,...,y_n) := (\exists x) \bigwedge_{i \leq n} \phi(x;y_i)$. We show
that combinatorial and classification theoretic properties of the
characteristic sequence reflect classification theoretic properties of
$\varphi$ and vice versa.