Boxology

Abstract: The paper proposes a formal approach for constructing UML activity diagrams from sequence diagrams by using graph transformations. Activity diagrams are good at describing the overall flow of control in a system, as they provide support for conditional and parallel behaviour, but do not capture well object interactions. Activity diagrams are mostly used in the preliminary stages of analysis and design. As the design progresses, more detailed descriptions of object interactions become necessary, and interaction diagrams are used for this purpose. During the transition from a high level to a detailed design, the mapping between the behavior represented in activity diagrams and that described in interaction diagrams may be lost, and the two views may become inconsistent. By reconstructing the activity diagrams from sequence diagrams, consistency is re-enforced. Every activity block is cross-referenced with the corresponding sequence diagram messages, which helps designers to correlate the two views. The transformation from sequence to activity diagrams is based on PROGRES, a known visual language and environment for programming with graph rewriting systems.

Abstract: Therearetwo categoriesof objects spatialinformation science investigates: actual objects and their spatial properties, such as in geography, and abstract objects which are employed metaphorically, as for visual languages. A prominent example of the latter are diagrams that model knowledge of some domain. Different aspects of diagrams are of in- terest, including their formal properties or how human users work with them, for example, with diagrams representing sets. The literature about diagrammatic systems for the repre- sentation of sets shows a dominance of region-based diagrams like Euler circles and Venn diagrams. The effectiveness of these diagrams, however, is limited because region-based diagrams become quite complex for more then three sets. By contrast, linear diagrams are not equally prevalent but enable the representation of a greater number of sets with- out getting cluttered. Cluttered diagrams exhibit inherent complexity due to overlapping objects, irrelevant details, or other reasons that impinge upon their legibility. This study contrasts both types of diagrammatic systems and investigates whether the performance of users differs for both kinds of diagrams. A significant difference can be shown regard- ing the number of diagrams that can be drawn within a fixed period of time and regarding the number of errors made. The results indicate that linear diagrams are more effective by being more restrictive and because region based diagrams show much clutter due to overlapping, coincident, and tangentially touching contours, as well as an overwhelming number of empty zones. Linear diagrams are less prone to errors and do not suffer from clutter.

Abstract: A new kind of a decision diagrams are presented: its nodes correspond to all types of nonsingular expansions for groups of input variables, in particular pairs. The diagrams are called the Linearly Independent (LI) Decision Diagrams (LI DDs). There are 840 nonsigular expansions for a pair of variables, thus 840 different types of nodes in the tree. Therefore, the number of nodes in such (exact) diagrams is usually much smaller than the number of nodes in the well-known Kronecker diagrams (which have only single-variable Shannon, Positive Davio, and Negative Davio expansions in nodes). It is usually much smaller than 1/3 of the number of nodes in Kronecker diagrams. Similarly to Kronecker diagrams, the LI Diagrams are a starting point to a synthesis of multilevel AND/OR/EXOR circuits with regular structures. Other advantages of LI diagrams include: they generalize the well-known Pseudo-Kronecker Functional Decision Diagrams, and can be used to optimize the new type of PLAs called LI PLAs. Importantly, while the known decision diagrams used AND/EXOR or AND/OR bases, the new diagrams are AND/OR/EXOR-based. Thus, because of a larger design space, multi-level structures of higher regularity can be created with them. This paper presents both new concepts and new efficient synthesis algorithms.

Abstract: The marking of graph diagrams (that is to say diagrams that are composed of nodes, possibly joined by edges) is tedious if the diagrams are presented on paper. If the key content of the diagrams is available in electronic form then the marking can be much more efficient. This is achieved because the tutor only has to mark each different diagram element once and this mark is transmitted to all diagrams that contain the element. This benefit to the tutor is obtained by requiring the students to use a diagram drawing program of some kind. However using such an editor can simplify the process for the students by allowing them to concentrate more on the problem and less on its graphical representation. The students can also be rewarded for going to this extra effort by receiving a much more detailed, personalised commentary on their work than would have been possible before, given the same amount of tutor time. We present the evolution of a drag-and-drop diagram editor specialised for the area of ER diagrams and an associated marking system with a simple but effective feedback mechanism. Some results from initial trials are presented along with some ideas for improvement and extension.