The theories and practices of software engineering and of human-computer interaction have, to a great extent, evolved separately. It seems obvious that the development of an interactive system would benefit from input from both disciplines. In practice, however, the communication between the two communities has been difficult. Models can be a particularly good tool for communication. For that to happen the differences between the models used by each community must first be identified and understood. This paper looks at the gaps between the models used by the software engineering and the human-computer interaction communities. It identifies where differences between these models can be found, and some aspects that need addressing in order to promote better communication.