Highlighting table relationships with colored rectangles shapes in Model view

Many time it happens that single report can contain several tens of tables and model view looks to wide even if arranged so well. at a later date, it may be difficult to recognize what all they represent in the lack of some visual classification.

I think it will be good idea to provide feature of adding colored transparent rectangles over the tables in Model view to show kind of group of process the tables represent. These may be kind of standard rectangle shapes seen in Microsoft word etc and can be resized as per user needs.

For example just a blue colored rectangle user can put of a block of tables to show tables related to manufacturing process and a red block to show QA related tables.

I can not attach a sample image here, otherwise I prepared one to clarify what I intend to say above.