Today, the development life cycle of 3D User Interfaces (UIs) mostly remains an art more than a principled-based approach. Several methods [1,3,7,8,9,10,11,15,17,18,19] have been introduced to decompose this life cycle into steps and sub-steps, but these methods rarely provide the design knowledge that should be typically used for achieving each step. In addition, the development life cycle is more focusing directly on the programming - sues than on the design and analysis phases. This is sometimes reinforced by the fact that available tools for 3D UIs are toolkits, interface builders, r- dering engines, etc. When there is such a development life cycle defined, it is typically structured into the following set of activities: 1. The conceptual phase is characterized by the identification of the content and interaction requests. The meta-author discusses with the interface designer to take advantage of the current interaction technology. The int- face designer receives information about the content. The result of this phase is the production of UI schemes (e. g. , written sentences, visual schemes on paper) for defining classes of interactive experiences (e. g. , class Guided tour). Conceptual schemes are produced both for the final users and the authors. The meta-author has a deep knowledge of the c- tent domain and didactic skills too. He/she communicates with the final user too, in order to focus on didactic aspects of interaction. 2.
