  Geometrical constructions using flexible cords have been known since the
earliest days of recorded mathematics. In this paper we introduce rigorous
definitions for two classes of string networks. A taut network is one in which
all cords are tight in every possible configuration; a tense network has
configurations in which one or more cords are not tight, but is externally
constrained to avoid such configurations. We show that taut networks compute
only affine linear functions and subspaces, whereas tense networks (which are
closely related to linkages) can trace any algebraic curve.
