As human's tasks with computers are becoming everyday life, HCI (Human-Computer Interaction) research has received a great interest in recent days. One of the objectives of HCI research has been to find the ways to design more consistent systems. To evaluate consistency from the user's viewpoint, TAG is thought to be advantageous among several suggested interface models including GOMS and GTN. TAG specifies actions to perform tasks in terms of rule schemas. It was verified that the less the number of rule schemas are, the better users perform the tasks due to assumably higher consistancy.
This paper hypothesizes that the consistency of systems depends not only on the number of rule schemas but also one the distances between rule schemas. That is, closer the rule schemas are, the easier it is to acquire the whole set of rule schemas. An experiment was conducted and supported this hypothesis. When designing systems, the results suggest distances between rule schemas should be considered as well as the number of the schemas.
