Task Action Grammar (TAG), which was proposed by Payne and Green(1989), is a formal representation of command language that highlights the syntactic structure(Panye and Green, 1983). With regard to graphic user interface(GUI), Howes and Payne(1990) conducted similar analysis for menubased softwares.
In this study, two propositions are presented. First, the difference of modalities of task features may hamper the integration of the same syntactic structure into one syntactic rule schema. Second, simply increasing the number of syntactic rule schemas does not severely impede user's learning of the interface provided that the modality of the display features corresponds well to that of the task features.
To verify these propositions, two systems performing procedural tasks were made : system 1 of which syntactic structures conflict with the modalities of the task features and display features and system 2 of which syntactic structures have well-matched modalities. In system 1, tasks with conflicting modalities between task features and display features produces more procedural errors than that with matched modalities although those two groups share the same syntactic structure. Comparing the performance of system 1 and system 2, in contrast to TAG's prediction, system 2 with more syntactic structures showed better performance, namely less number of errors, than system 1.
The conclusion is that, especially in analyzing GUI Softwares, the modal compatibility between tasks and displays plays a critical role as well as the syntactic structure. Thus, it is suggested that the designers of user interface should take account of semantic characteristics such as compatibility of modalities between task features and display features.
