Database Reference
In-Depth Information
tools can be a real pain. If you work on paper, you may end up starting half a dozen times be-
fore you get a good arrangement. If you use a typical drawing program (the drawing capabil-
ities in Word, for example), then you can spend copious hours reconnecting lines and entit-
ies, reshaping lines, and hand drawing crow's feet as you move things around. See the box
below for some suggestions to solve this problem.
When you're done, you should have a single, unified diagram with each entity showing up
only once, and every relationship indicated by a line. When you're thinking about relation-
ships with just pairs of tables, you don't get the big picture. The ER diagram shows you how
everything
comes together, and when that happens, you often discover tangles of relation-
ships just like those in
Figure 5-6
. Tangles like these aren't inherently bad; they're just usu-
ally completely unnecessary. Take the first tangled group—Expenses, Jobs, and Customers.
The diagram tells you that customers have jobs, jobs have expenses, and customers have ex-
penses.
POWER USERS' CLINIC: IT'S ALL ABOUT THE TOOLS
If you plan on creating more than one ER diagram, or if you have a complicated one to create, dia-
gramming software will save you lots of time and heartache. Microsoft Visio
(
www.microsoftstore.com/Microsoft_Visio
)
and SmartDraw (
www.smartdraw.com
)
are two choices
for Windows. Try OmniGraffle (
www.omnigroup.com/OmniGraffle
)
or ConceptDraw for Mac OS
X (
www.conceptdraw.com
)
. If none of these fit the bill for you, do a web search for
ER diagram
to
see what new diagramming programs have hit the market. You'll even find some free, online-only
diagramming tools, if that's what your budget calls for.
The beauty of all of these tools is that they
understand
ER diagrams. They can hook entities togeth-
er with ease, draw crow's feet on your behalf, and keep everything connected as you move your en-
tities around to find a good arrangement. One caveat: Some of these programs have built-in database
diagramming features, but they're too complex for FileMaker work. The main capabilities your soft-
ware package needs are drawing a box and labeling it and adding crow's feet to your lines.
If you're an unrepentant cheapskate, here's a tip: Write the entity names on a piece of paper, and cut
out each one. Then arrange them on paper, draw lines, and see how it looks. You can slide the entity
scraps around a few times to find a decent arrangement and then commit the whole thing to a clean
piece of paper.
