The signaling networks include several hundred components, all connected in a discrete manner. (a) Example network. Each circle represents a component in the network; lines represent connections between them (that is, rules). Key signaling components are noted. (b) A small subnetwork. (c-e) Examples of data used to populate the model. Each histogram shows the distribution of expression values across the complete panel of cell lines. Data for each component in the model were clustered individually to determine whether or not the component should be included in the initial state. Components that clustered into two groups were present in the initial states of some cell lines and absent from others. (c) Raf1 transcript data yields a single group. (d) ErbB4 protein data yields two groups. (e) EsR1 yields three groups.