| OCR Text |
Show 18 MINI is a convenient tool, since the system designer is permitted to modify a grammar without rewritting an entirely new parser. However, since the recovery mechanism of MINI is not entirely satisfactory, this may be a serious problem. Even if MINI were not used, and a custom parser was written this issue would still have to be adequately addressed. Therefore, a designer should be thoroughly familiar with the syntax of these grammars before using GCS. The BNF for these grammars is presented in Appendices A, 8 and C. }·~ The Graphical Implementation Since a state or a transition in a state-machine may contain a lot of information, displaying all these details on the screen at the same time could result in a messy screen and the designer will not be able to immediately grasp the overall design at any stage. Thus, the abstract level of the state-machine which is graphically displayed at the top-level frame is represented by state boxes with the state name in the center which are interconnected with transition arcs from one state to another. All other details about states and transitions are maintained in the database. GCS is equipped with "Zooming" menu items for observing these details about states and transitions. Therefore, a designer is able to review the whole design and also to examine some detailed information. As transformations such as scaling and translation are employed to manipulate the graphical representation of the state-machine in GCS, a device independent description is used graphical symbol. GCS applies transformation to implement each functions to these absolute coordinates before displaying them onto the top-level frame. |
