When a diagram starts to have too many objects, it becomes impossible to follow the relationship lines. Adding layers would work like this:
A table could belong to one or more user defined layers, and the user can turn on or off the visibility for each layer. For example, I could turn off all layers except for the 'accounting' layer, and I'd have a very clear view of those objects and their relation.
I don't know why no ER diagraming solution has a layering feature but this should be a must for professional diagrams, this could set you miles apart from other solutions.
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