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Chapter 48. Coherent Objects > Coherent Application - Pg. 158

Coherent Objects 158 Fitting Ideas Visual Coherence is a measure of the fit between the visual organization of objects as they appear on the user interface and the conceptual organization of the ideas those objects represent. A more coherent and comprehensible user interface results when things that are thought of together appear together and things that are not thought of together are separated. To measure Visual Coherence in practice you need to know two things. You need to know what the semantic groupings are for the concepts represented by visual objects appearing on the user in- terface, and you need to identify the visual groupings on the user interface itself. Fortunately, modern graphical user interface design practices make it fairly easy to identify the visual groupings. User interface designers put lines or rules between sections of a dialog. They draw a border around a set of option buttons or make a frame around a toolbar. They may shade the background differently in one part, or make it appear to be raised from the screen or depressed into it. Or they may do no more than leave a little extra space between one group of command buttons and another. In any case, it is usually quite easy to eyeball the user interface and draw lines around the various visual groupings. Semantic grouping, being invisible and intangible, is a little trickier. Fortunately, a good domain object model helps. Domain classes, their methods, and their attributes define one view of the se- mantic organization associated with a given application. Through a simple exercise of sorting through the basic concepts embodied in an application, we can define clusters of related concepts based primarily but not exclusively on the domain class model. Computing Visual Coherence then becomes easy. It is only necessary to look at every pair of visual components in each visual group and count the number of pairs where both visual components are associated with the same semantic cluster. Visual Coherence is just the number of pairs in which