Database Reference
In-Depth Information
Introducing complexity through join tables
Let's take the model, which was described previously, to the database administrator
for an actual implementation. What happens then is that in this implementation, the
relational model inherently causes complexity. What you can see in the following
diagram is that for every relationship where we can have
n-n
combinations, we
actually need to introduce something that links the two tables together. This is what
we call a join table, and this will be used by every query that requests a combination
of the
n-n
entities.
The database schema
In the previous example, we introduced the
AppDatabase
table to link applications
to database servers and the
UserApp
table to link
Users
to
Applications
. These join
tables are only necessary to deal with the shortcomings of the relational model, and
they complicate our lives as database administrators and application developers.
They introduce unwanted complexity.
