Making Data Models Readable - High-Performance Web Databases: Design, Development, and Deployment - page 238

structure, the more likely it is to be able to resist requirements for fu-
ture changes. To the system designer and builder, it sends the mes-
sage: “This (rigorously described) is what you are to build.”
Because data modeling was created within the computer industry, the
second objective has often taken priority. As drawn by systems engineers,
data models tend to look like electronic schematics — to be read only by
other engineers. The morass of boxes and lines makes them quite formida-
ble to all but the most dedicated reader. Many data modeling conventions
— and a great many data modeling practitioners — do not put enough
weight on the importance of making the model accessible to the outside
world. Indeed, some contend that the models cannot be made accessible to
the outside world, so there is no point in even trying.
This article takes the position that not only is it possible to produce
model drawings that can be understood by potential systems users, but it
is the modeler's responsibility to do so. Some guidelines for producing
model drawings follow.
There are two major issues in the readability of models. The first, and
the one to be discussed most, is aesthetic. How is the drawing constructed
and to what visual effect? The second is the way things in it are named. Are
the words on the diagram helpful in divining its meaning?
AESTHETICS
Data modeling was originally an engineering discipline, not an artistic
one. For this reason, most modelers pay less attention to aesthetics than
they should. Part of the problem is the system of notation they use. Some
notations lend themselves to improved aesthetics, while others produce
drawings that are nearly impossible to read, regardless of what the mod-
eler does. The rest of the problem is in the way the modeler does his work.
The aesthetic considerations to be discussed are:
1. The ordering or arrangement of symbols on the model
2. The number of symbols on the model
3. The number of symbol types there are
4. How the various layers of the model interact with each other
The modeler has control over the arrangement of the drawing, the num-
ber of symbols he uses, and the overall layering of the diagram. The system
of notation chosen also affects layering, and determines the number of
kinds of symbols that will be present.
Order
How the entities are placed on a page is critical to the viewer's ability to
understand a diagram. Typically (especially if the model was produced via