Making Data Models Readable - High-Performance Web Databases: Design, Development, and Deployment - page 250

Exhibit 16-13. Too many lines.
The way to avoid bending lines, of course, is to stretch the entities as nec-
essary. (CASE tools which do not allow this are particularly reprehensible.)
Exhibit 15 shows how straighter lines give the entities much greater impact.
Layering. Edward Tufte has said that “among the most powerful devices
for reducing noise and enriching the content of displays is the technique of
layering and separation, visually stratifying various aspects of data … the
various elements of flatland interact creating non-information patterns and
texture, simply through their combined presence.” 11
Tufte's idea of layering is that different kinds of information should be
represented in sufficiently different ways that one can view only part of the
picture at once, and easily ignore the rest. When attributes are represented
as symbols in their own right, as in the Chen and the ORM techniques, they
have the same status on the diagram as entities. Similarly Chen's relation-
ship symbols make the viewer see a relationship as another object on the
same level as an entity, even though semantically he specifically wants it to
be considered as different from an entity. That means that the viewer must
deal with entities, relationships, and attributes at the same time, with all
competing for attention. The graphic distinctions between completely dif-
ferent kinds of information are small.