Making Data Models Readable - High-Performance Web Databases: Design, Development, and Deployment - page 254

The solid line half means “must be” (lower limit one) and the dashed line
half means “may be” (lower limit zero).
WHAT TO DO?
So, what is a person to do to make a diagram that is attractive and easy
to read?
• Limit what you are trying to present to that which is meaningful and
important to your audience. While it is desirable to present as much as
possible, this exercise rapidly reaches the point of diminishing re-
turns, where the addition of more information to the drawing actually
subtracts from its overall effectiveness. Among other things, this
means:
— Using as consistent and spare a notation scheme as possible.
— Limiting the number of objects appearing on a diagram.
• Arrange the diagram in a rational way.
• Make sure that your names are meaningful and clear.
• Use patterns that have been tested.
PRESENTING YOUR MODEL
As important as the construction of a model is, it is equally important to
present it in a way that permits the viewer to ease his way into the con-
cepts involved. Models can be presented in an understandable way if a few
rules are followed.
First of all, be sure to begin the session with a careful and thorough
explanation of just what the objectives are. One cannot build a system
without the viewers' assurance that their business is understood. This
technique is intended to show them what is understood, so that correc-
tions can be made if necessary. The presenter is there to be wrong, since it
is much cheaper for him or her to be wrong now, than it is to wait and be
wrong in the design of a system. The presentation is in terms of the struc-
ture of their data, so by extension, it is really about the structure of their
business. Admit that the technique is a bit arcane and point out that it
examines business from a perspective which may be unfamiliar to them, so
ask their indulgence.
Then, do not begin by presenting a completed model. Even the most
artistic model is too frightening to see as a whole. Begin by presenting a
slide with one entity. Discuss that entity. What does it mean? What are its
attributes? Can you think of any examples?
Add another one, with a relationship between the two. Discuss the sec-
ond entity. Then discuss the relationship. Is it true that it must be related
to only one? Can a case ever be imagined where it is related to more than
one? Then add a couple of more entities and relationships at a time, dis-