ITS@PennState
MS Access:
Creating
Relational
Databases
ITS@PennState
224B Computer Building
University Park, PA 16802
seminars@psu.edu
http://its.psu.edu/training/
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Table of Contents
Objectives ........................................................................................................2
Database Normalization Terminology ..............................................................3
First Normal Form ............................................................................................4
Second Normal Form .......................................................................................5
Third Normal Form………………………. …......................................................7
Relating Tables Terminology ...........................................................................8
One-to-One Relationship .................................................................................9
One-to-Many Relationship .............................................................................11
Many-to-Many Relationship ...........................................................................12
Implementing Referential Integrity .................................................................15
Orphan Records.............................................................................................16
Cascading Deletes .........................................................................................16
Testing Cascading Deletes ............................................................................17
Cascading Updates........................................................................................17
Testing Cascading Updates ...........................................................................18
Independent Practice Activity .........................................................................18
Additional Resources .....................................................................................19
Objectives

Learn how to normalize tables to reduce data redundancy

Understand the requirements for first, second, and third normal forms

Learn how to set one-to-one, one-to-many, and many-to-many relationships
between tables

Implement referential integrity between related tables

Use cascading deletes and updates to prevent orphan records
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Databases
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Database Normalization Terminology
Normalization
the process of restructuring data files to 1) reduce data to
its simplest structure, 2) minimize redundancy, and 3)
achieve the most efficient and functional yet flexible way to
store data
First Normal Form (1NF)
eliminates duplicate data
 a table should not contain similar information in
several fields; eliminate duplicative columns from
the same table or move repeating fields to a related
table
 a table should not contain fields that can be further
broken down into smaller meaningful parts
 create separate tables for each group or related
data and identify each row with a unique column
(the primary key); each table should describe a
single entity (object) class
Second Normal Form (2NF)
requires all data in the table apply directly to the subject of
the table indicated by the primary key field
 if the table has a single-field primary key and meets
the requirements for 1NF, then it also meets the
requirements for 2NF
 however, if the table has a composite (multiple-field)
primary key, then all the fields in the table must be
related to and/or dependent on ALL the fields of the
composite primary key
 to convert a table to 2NF, find all the fields that are
related to only part of the composite (multiple-field)
primary key, group these fields into another table,
then assign a primary key to the new table
 another way of looking at it is to remove ALL
subsets of duplicate/redundant data that apply to
multiple rows of a table and place them in new
tables, then create relationships between these new
tables and the original tables by using foreign keys
Third Normal Form (3NF)
eliminates fields that can be derived from other fields
 if a table contains fields that do not relate to and are
not fully dependent on the primary key and
completely describe the object that table represents,
then it is not in 3NF
 to convert a table to 3NF, delete all the fields that do
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Databases
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not relate to the primary key
Fourth Normal Form (4NF)
requires that tables not contain fields for two or more
independent, multi-varied facts
 this rule requires splitting tables that consist of lists
of independent attributes
 i.e. in a relation table, job skills and language
fluency are independent facts about an employee;
therefore, the 3-field relation table must be split into
2 two-field relation tables
Fifth Normal Form (5NF)
requires the capability to reconstruct the source data from
the tables that have met 1NF, 2NF, 3NF and 4NF
 you should be able to regenerate from the database
a spreadsheet that contains all the data in the
original version
 this is an “acid test” for normalization and requires
considerable skill in designing queries to join related
tables to produce a readable output to compare wit
the original data
Before 1NF
Observe the
Name field. It
contains both
first and last
names. This is
not in 1NF.
MS Access: Creating Relational
Databases
Observe all of the Project number fields. These
fields can be combined into one field called
Project_number. As it stands now, it is not in
1NF.
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After 1NF
The Project
number fields
have been
combined into
one field
The Name field
has been divided
into two separate
fields
Before 2NF
Together, the
Employee_code
and the
Project_number
make up a
composite
(multiple-field)
primary key
MS Access: Creating Relational
Databases
Observe the
First_name,
Last_name and
Region fields.
These fields
have repetitive
values. You can
divide the data
into two tables.
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After 2NF
The table has Employee_code,
First_name, Last_name and
Region fields. All the fields in
the table relate to the
Employee_code field which is
the primary key.
This table contains Employee_code,
Project_number and Earnings fields. The
Earnings field relates to both the
Employee_code and Project_number
fields which together form the composite
(multiple-field) primary key.
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Databases
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Before 3NF
The table contains a
Dept_name field which relates
to the Dept_code field.
And, the Dept_code field
relates to the Employee_code
field (primary key).
However, the Dept_name field
does not directly relate to the
Employee_code field (primary
key). It is dependent on the
Dept_code field.
After 3NF
The table contains
Employee_code, First_name,
Last_name, Region and
Dept_code fields. All of these
directly relate to the
Employee_code field (primary
key).
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Databases
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The table contains Dept_code and
Dept_name fields. Dept_name directly
relates to Dept_code (primary key).
Relating Tables Terminology
Relationships
used to extract data from several tables at the same time
Primary key
unique identifier for each record in a table
Foreign key
the primary key in the related table
Referential integrity
ensures that changes made to one table will be reflected in
the related table
One-to-one relationship
when one complete record in the primary table is related to
just one record in the related table and vice versa; both
tables are equally dependent on each other
One-to-many relationship
when one record in the primary table is related to several
records in the related table; however, a record in the
related table has only one related record in the primary
table
Many-to-many relationship
when several records in one table are related to several
records in another table. A many-to-many relationship
cannot be created directly in MS Access. To relate such
tables, you must first create a junction table that contains
the primary keys of both tables
Junction table
a table which has a primary key that’s actually a
combination of at least the primary keys from two or more
tables; a junction table acts as a bridge between the two
tables in a many-to-many relationship
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Databases
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One-to-One Relationship
First, go to the Tools menu and
choose Relationships.
Then, click on the Show Table icon
on the toolbar.
Click on the Tables tab.
Select Sales_employees.
Click the Add button.
Select Sales_payroll.
Click the Add button, then click the
Close button.
Drag the Employee_code field
(primary key) from the
Sales_employee table and drop
it on the Employee_code field in
the Sales_payroll table.
Notice the Relationship Type at the bottom of
the window says, “One-To_One.”
Click on the Join Type button.
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Databases
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Click OK
The first option
creates a one-toone relationship
and is selected
by default.
Check Enforce Referential
Integrity, then click on the
Create button.
Observe the line connecting the two
tables and the number 1 at each end of
the line indicating this is a one-to-one
relationship.
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Databases
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One-to-Many Relationship
Drag the
Dept_code field
(primary key)
from the
Departments
table and drop it
on the
Dept_code field
(foreign key) in
the Employees
table.
Click on the Show
Table icon on the
toolbar, then add
the Departments
and Employees
tables.
Notice the Relationship Type at the
bottom of the window says, “OneTo_Many.”
Click on the Join Type button.
Select the second option. This
will create a one-to-many
relationship between the tables
and will ensure that 1) each
record in the Employees table has
a corresponding record in the
Departments table and 2) that
each record in the Departments
table can have multiple records in
the Employees table. Click OK.
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Databases
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Check Enforce Referential
Integrity.
Click the Create
button.
Observe the line
connecting the two tables
and the number 1 near
the Departments table
and the infinity symbol
near the Employees table
indicating this is a one-tomany relationship.
Many-to-Many Relationship
Click on the
Relationships
icon on the
toolbar
Open the
Transaction
database
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Databases
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Click on the Show
Table icon on the
toolbar and add the
Customer,
Order_details and
Products tables to the
Relationship window.
Drag the Customer_ID field from the Customers table
to the Customer_ID field in the Order_details table.
In the Edit Relationships window,
click the Join Type button.
Select the second option for a oneto-many relationship between the
Customers and Order_details
tables.
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Databases
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Check Enforce
Referential Integrity.
Click the Create
button.
Now, repeat this procedure and create a one-to-many relationship
between the Product and Order_details tables.
There is a one-to-many relationship between Customers and Order_details and a oneto-many relationship between Products and Order_details. The Products and
Customers tables have a many-to-many relationship that is defined by both tables
have a one-to-many relationship with Order_details which is the junction table.
It is a junction table
because it acts as a
bridge between
which customers
bought each type of
product in each
order transaction.
Observe the
Order_details
table.
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Databases
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Implementing Referential Integrity
Open the Customers table, then go
to the Window menu and choose
1Transactions: Database (Access
2000 file format)
Open the Order_details table,
then go to the Window menu and
choose Tile Horizontally.
In the Order_details table, observe the
Customer_ID and the Order_ID. Notice that
a customer can place several orders.
However, for each Order_ID there is only
one Customer_ID. This means that only
one customer can place an order. There
can’t be multiple customers for each
individual order.
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Databases
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Enforcing referential integrity means that since there is a relationship between the
Customer table and the Order_details table, if a customer is deleted out of the Customer
table, then all the orders placed by that same customer will also be deleted.
Orphan Records
If you set a relationship between two tables, then the related table should always have a
corresponding record in the primary table. If data is modified or deleted in the primary
table, then the related table should also be updated. If you accidentally delete a record
without deleting the related records in the other table, then that table will contain orphan
records. Orphan records are no longer related to anything in the primary table.
Cascading Deletes
You can enforce referential integrity to cascade deletes on records in related tables.
When you use cascade deletes to delete a record from a primary table, MS Access
automatically deletes all related records from other related tables. This ensures that there
are no orphan records.
Check Enforce
Referential
Integrity and
Cascade
Delete Related
Records
MS Access: Creating Relational
Databases
Click OK
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Testing Cascading Deletes
When you delete a record in the primary table, a message box will come up stating that
cascading deletes will cause records in related tables to also be deleted.
Cascading Updates
You can enforce referential integrity to cascade updates to related records in related
tables. This means that whenever you change a primary key in a table, the change is
updated in all of the related tables.
Check Enforce
Referential
Integrity and
Cascade
Update Related
Fields
MS Access: Creating Relational
Databases
Click OK
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Testing Cascading Updates
Try changing the primary key in the primary table, then check to see if it was updated in
the related tables.
Independent Practice Activity
Open Relational_databases
Open the Relationships window
Create a one-to-many relationship between the Retailer and Transaction tables. The
relationship should include all of the records from Retailer and only those records from
Transaction where the joined fields are equal
Create a many-to-many relationship between the Retailer and Product tables by creating
a one-to-many relationship between the Product and Transaction tables
Save the relationships
Compare the Relationships window to the diagram below:
Enforce cascading deletes between the Retailer and Transaction tables
Update the relationship
Test cascading deletes between the Retailer and Transaction tables
Enforce cascading updates between the Retailer and Transaction tables
Update the relationship
Test cascading updates between the Retailer and Transaction tables
Close the database
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Databases
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Additional Resources
MS Access 2002 Help
Help menu (Contents, Answer Wizard, Index tabs)
F1
Ask a Question box
Office Assistant
Books
Special Edition Using Microsoft Access 2002 by Roger Jennings
The Complete Reference: Access 2002 by Virginia Andersen
Mastering Access 2002 by Alan Simpson and Celeste Robinson
Teach Yourself Microsoft Access 2002 Visually by Ruth Maran
Instant Access Databases by Greg Buczek
Microsoft Access 2002 Bible by Cary N. Prague and Michael R. Irwin
Sams Teach Yourself Microsoft Access 2002 in 10 Minutes by Faithe Wempen
Microsoft Access 2002: At A Glance by Perspection
Microsoft Access 2002: Step By Step by Catapult, Inc.
Running Microsoft Access 2002 by John Viescas
Microsoft Pocket Guide to Microsoft Access 2002 by Stephen L. Nelson
Websites
http://its.psu.edu/training/
http://www.fgcu.edu/support/office2000/access/index.html
http://www.cant.ac.uk/title/tutorials/access.htm
http://www.microsoft.com/office/access/default.htm
http://www.microsoft.com/office/access/using/default.htm
http://www.cyber-matrix.com/access.htm
http://www.course.com/downloads/NewPerspectives/office2000/access_main.html
http://www.customguide.com/demos/access2000_2.pdf#page=13
http://databases.about.com/cs/tutorials/
http://ittraining.westmont.edu/access/tutorials.html
http://cisnet.baruch.cuny.edu/holowczak/classes/2200/access/accessall.html
Phone Numbers
Help Desks (215 Computer Bldg 863-2494 and 2 Willard Bldg 863-1035)
Seminar Line 863-9522
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Databases
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