Download Introduction to Microsoft Access and Relational Databases

Introduction to Microsoft Access
and Relational Databases
A Database Management System (DBMS) is the software used to create databases.
Microsoft Access is an example of a DBMS. A database is a collection of data organized
into tables. The database we are creating is called Bavant Marine Services.
Data tables are made of columns called fields and rows called records. Our database
consists of two tables, the Marina table and the Technician table, but most databases will
have many more tables.
DBMS
(MS Access)
creates
Databases
(Bavant Marine Services)
contain
Tables
(Marina)
Customer Table
records
fields
In addition to tables, databases can contain forms, reports, and queries, as well as many
other objects. A form is used to view, edit, and enter data in the database tables. A
report is used to display and print data from database tables. A query is used to answer
questions about the data.
Forms
Databases
Reports
(view, edit, & enter data)
(contain data in tables)
(display & print data)
Queries
(use data to answer questions)
A relational database uses primary keys and foreign keys to create relationships between
tables.
A primary key is a field that uniquely identifies a record. No two records will have the
same primary key. In the Customer table, Cust ID is the primary key field. The table
includes first name and last name fields. However, it is entirely possible that there could
be two people with the same first and last name in the same database table. To eliminate
confusion, it is necessary to have a field, like Cust ID in the Customer table, that uniquely
identifies each record.
A foreign key is data field that appears in one table but is also a primary key in another
table. Foreign keys are used to establish relationships between tables. As mentioned
before, the Cust ID field is a primary key in the Customer table. Cust ID also appears in
the Order table, but not as a primary key. Rather than list customer name address and
phone number fields again in the Order table, customers are identified by the Cust ID
field.
Customer Table
Cust ID is a primary
key in the Customer
table. In the Order
table Cust ID is a
foreign key. Thus, a
relationship
exists
between the tables.
Order Table
A relational database uses these relationships to eliminate or control redundancy. A
redundancy occurs when the same data appears in more than one place in the database.
To understand why redundancies should be controlled, imagine a database where
customer information and orders exist in the same table. Since one customer could place
many orders, that customer information would appear in several places in the Customer
Order table.
Customer Order Table
redundant data
This table illustrates three problems caused by redundancy:
1. Inconvenience: Entering the same data for multiple records is a waste of time. In the
Customer Order table above, John Smith’s name, address, and phone number has to
be entered each time John places an order. When customer information and order
information were in separate tables, the personal information of each customer only
had to be entered once and a Cust ID primary key could be used to associate
customers with their orders.
2. Inefficiency: Redundancy is a waste of space as well as a waste of time. While the
Customer table currently only has two redundancies right now, as more redundant
data is entered, more storage space will be used to save the data table. The larger the
database, the more space could be wasted if redundancies go uncontrolled.
3. Inconsistency: When the same data appears in more than one place, like the customer
information for Jane Doe, database users may only update information in one location
but not in another. Notice that Jane Doe’s name and address are different in the
second and fourth records. When data inconsistencies exist, it may be hard to
determine which record has the correct information.
Database administrators try to design databases with as little redundancy as possible. The
process of controlling redundancy is called normalization.
Questions on MS Access and Relational Databases…
1. What is the difference between a DBMS and a database?
2. What are the rows and columns called in a database table?
3. The following picture is an example of what kind of database object? For what
purpose is this object used?
4. The following picture is an example of what kind of database object? For what
purpose is this object used?
5. The following picture is an example of what kind of database object? For what
purpose is this object used?
6. What is the difference between a primary key and a foreign key?
7. How is a relationship established between two tables?
8. What is a redundancy? Why is it a problem?
9. What is normalization?
10. What could you do to eliminate redundancy in the following database table? What
tables would you make? What would be your primary key and foreign key fields?