There is no major problem with this: most often the display will be updated anyway,
since most operations that affect it will be to closely related elements. In other cases, a
simple ???Refresh??? key will suf?¬?ce: users are accustomed to programs needing a little
nudge in these areas. If the content is valuable, it should not be thrown out because the
world is imperfect. Conversely, if the 100% accuracy of the content at all times is vital,
we can simply move the generation to a regular generator that is run on demand to
produce its output in a separate window.
Conditional Symbol Elements Property values and generated text elements
give us most of the dynamic behavior wewant in symbols, but in some cases we would
like to ???generate??? something other than text, for example vector graphics elements.
This may initially seem to be a task for tools where each symbol is hand programmed,
but on closer inspection that is unnecessary. The elements that are to be added are
WHAT IS NEEDED IN A DSM ENVIRONMENT 379
almost always known in advance, so they are not so much generated as displayed
conditionally on some value from the model.
Most commonly such elements are small icons or single icon-like characters,
displayed based on a property whose value is a Boolean or a selection from a ?¬?xed list
or other enumeration.
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