Database Reference
In-Depth Information
Note
Before you begin to work through the examples in the remainder of the chapter,
now is a good time to remember a principle I presented in the introduction:
Focusontheconceptortechniqueanditsintendedresults,
not on the example used
to illustrate it.
There are, without a doubt, any number of ways in which you can relate the tables in these
examples (and also in the case studies), depending on each table's role within a given data-
base. The manner in which I use the examples here is not important; what is important are
the techniques I use to identify and establish relationships between tables. Once you learn
these techniques, you can identify and establish relationships for any pair of tables within
any context you may encounter.
Now that you've learned about the various types of table relationships, your next task is to
identify
the relationships that currently exist among the tables in the database.
Identifying Existing Relationships
When you were composing the table descriptions earlier in the database design process
agementtohelpyouwiththattask.Thesepeoplewerealsodesignatedasrepresentativesof
theorganizationandgrantedtheauthoritytoaidinthedecision-makingprocessthroughout
the remainder of the database design process. (At least, this is the current assumption for
the sake of discussion and example.) Now you'll arrange meetings with this group once
againsothattheycanhelpyouidentifyexistingtablerelationships.Thesefolkscanprovide
valuable input because they are likely to have a good perspective on how various subjects
(ortables)arerelated.Althoughtheirperceptionsofthemannerinwhichthesesubjectsare
related may not always be complete or accurate, their contributions will still be useful in
identifying most of the relationships.
Begin the process of identifying relationships by creating a matrix of all the tables in your
database. (You can do this on a sheet of paper, a white board, or a spreadsheet program.)
For example, assume you're working with these tables:
