Twidale, MichaelRodden, TomSommerville, Ian2017-04-152017-04-151993978-94-011-2094-4We describe the development of a system to support cooperative software design. An iterative development approach has been used, based upon the observation of system use in authentic design sessions. This allows us to correct interface errors, and also to learn more about the nature of collaborative design. The observations of use and the resulting refinements of the system are described. In particular we note the variability in design activity both amongst designers and according to circumstances. We also note the way in which concepts mutate over time (often involving frequent and rapid revision) leading to an evolution of structure.enText