Pathfinder and other tools for analyzing signal transduction networks

Many electronic design tools are, at their core, tools for analyzing interacting networks of components in which there is a definite causal sense of direction in each interaction: outputs affect inputs, but not vice versa. Simplifying or restricting a network of protein interactions so that this kind of directedness holds makes the same category of software tools applicable. In signal transduction cascades the direction is usually given by "kinase phosphorylates substrate." This paper examines a few kinds of directed network analysis tools in the context of signal transduction.