There are two ways of grouping tables together. The first is to use the layer tool found in the toolbar on the left when you are working with a diagram. Once you selected the tool you can click-then-drag to define your layer area. Then you can move existing tables into the layer region by using drag-n-drop. You can also drag tables from the catalog palette onto the layer.
The other way - which is very useful when working with really large models - is, to create several diagrams that represent different subsets of model objects. Workbench can hold an unlimited number of diagrams in one model file. And you can still use the layers described above in addition to that.
Both can be done by Lua scripts as well but I don't have any code to demonstrate that.
For Reverse Engineering you have to use File -> Import and work with SQL CREATE script files that can be created with MySQL Administrator or the mysqldump tool. Or you pony up the 99 bugs for Standard Edition which will give you an easier workflow:
http://dev.mysql.com/workbench/?page_id=11
Hope that helps,
Mike
Michael Zinner, Team Lead, Developer Tools
MySQL AB, www.mysql.com
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Edited 1 time(s). Last edit at 10/27/2008 11:33AM by Michael G. Zinner.