  We study a new class of networks, generated by sequences of letters taken
from a finite alphabet consisting of $m$ letters (corresponding to $m$ types of
nodes) and a fixed set of connectivity rules. Recently, it was shown how a
binary alphabet might generate threshold nets in a similar fashion [Hagberg et
al., Phys. Rev. E 74, 056116 (2006)]. Just like threshold nets, sequence nets
in general possess a modular structure reminiscent of everyday life nets, and
are easy to handle analytically (i.e., calculate degree distribution, shortest
paths, betweenness centrality, etc.). Exploiting symmetry, we make a full
classification of two- and three-letter sequence nets, discovering two new
classes of two-letter sequence nets. The new sequence nets retain many of the
desirable analytical properties of threshold nets while yielding richer
possibilities for the modeling of everyday life complex networks more
faithfully.
