Database Reference
In-Depth Information
Summary
The chapter opened with a discussion of the importance of
keys.
You learned that there are
different types of keys, and each type plays a different role within the database. Each key
performs a particular function, such as uniquely identifying records, establishing various
types of integrity, and establishing relationships between tables. You now know that you
can guarantee sound table structure by making certain that the appropriate keys are estab-
lished for each table.
We then discussed the process of establishing keys for each table. We began by identifying
the four main types of keys:
candidate, primary, foreign,
and
non-keys.
First, we looked at
the process of establishing candidate keys for each table. You learned about the Elements
of a Candidate Key and how to make certain that a field (or set of fields) complies with
these elements. Then you learned that you can create and use an artificial candidate key
when none of the fields in a table can serve as a candidate key or when a new field would
make a stronger candidate key than any of the existing candidate key fields.
The chapter continued with a discussion of
primary keys.
You learned that you select a
primary key from a table's pool of candidate keys and that the primary key is governed
by a set of specific elements. We then covered a set of guidelines that help you determine
which candidate key to use as a primary key. Next, you learned how to ensure that the
chosen primary key exclusively identifies a given record and its set of field values. When
the primary key does not exclusively identify a particular field value, you know that you
must remove the field from the table in order to ensure the table's structural integrity. You
also know that each table must have a single, unique primary key.
You then learned that you designate any remaining candidate keys as
alternate keys.
These
keys will be most useful to you when you implement the database in an RDBMS program
because they provide an alternate means of identifying a given record. We then discussed
the
non-key
field, which is any field not designated as a candidate, primary, alternate, or
foreign key. You now know that a non-key field represents a characteristic of the table's
subject and that the primary key exclusively identifies its value.
Table-level integrity
was the next subject of discussion, and you learned that it is estab-
lished through the use of primary keys and enforced by the Elements of a Primary Key.
The chapter closed with some guidance on conducting further
interviews
with users and
management. You now know that these interviews provide you with a means of reviewing
the work you have performed on the tables and help you to verify and validate the current
database structure.
