Introduction to MS Access, building tables, creating keys, creating relationships

BSAD 141Dave Novak

Topics Covered

Provide a brief introduction to MS AccessName and save a DB fileCreate tables and keysCreate and enforce relationshipsConvert a partial ERD to design in AccessProvide examples of both entity integrity and

referential integrity using Access

Important to note!

If you are having trouble keeping up with the lecture or having some type of technical problems, you may need to read and work through the Tech Plug Ins that are shown in the course schedule

These will walk you through the basic features in MS Access and guide you through table and key creation as well as how to create relationships between tables

Example: Partial ERD Consider a relationship between a manager

and a projectAssume the following:

• Each manager can manage up to 5 different projects simultaneously

• Each manager must manage at least one project• Each project is assigned to only 1 manager (there

are no co-manager leads on the project)• When entered into the DBMS, each project must be

assigned to a manager

Example: Partial ERD Draw the partial ERD – discuss degree,

connectivity, and existence

Two Types of RDBMS Integrity Rules 1) Entity Integrity

2) Referential Integrity

Building Tables in Access

Create a DB file called “class-example1” Build 2 separate tables that correspond to

the partial ERD you just drewAttributes for Manager (ManagerID,

FirstName, LastName, Address, Salary)Attributes for Project (ProjectID,

ProjectName, Duration, Phase) Model the relationship in Access and

enforce referential integrity

Building Tables in Access

1) Create the “shell” or empty tables to begin with

2) Specify the data type for each attributeManager (ManagerID (txt), FirstName (txt),

LastName (txt), Address (txt), Salary (currency))

Project (ProjectID (txt), ProjectName (txt), Duration (txt), Phase(txt))

Link the tables using a Foreign Key

Using our ERD and what you know about the location of Foreign Keys FK: Which table does the FK appear in?What is the FK attribute?Go into design view and add the FK attribute

Enter Data in Manager Table: Entity Integrity Error

You get an error message if you violate entity integrity rules

Manager

ManagerID FirstName LastName Address Salary

765-98-2222 Dave Smith 2 Main St. $75,000

123-45-6789 Sue Jones 1 East St. $80,000

Mary Wells 1 North St. $78,000

Complete Manager Table

Just use 5 attributes and enter 3 records I give you

Manager

ManagerID FirstName LastName Address Salary

765-98-2222 Dave Smith 2 Main St. $75,000

123-45-6789 Sue Jones 1 East St. $80,000

123-76-8823 Mary Wells 1 North St. $78,000

Enter Data in Project Table

Just use the 4 attributes and enter the 4 records I give you!

Project

ProjectID ProjectName Duration Phase

PRJ-145 Health Care Database 14 months 2

PRJ-147Traveler's Insurance Payroll

System 26 months 1

PRJ-151 Capital Finance Highway 41 7 months 1

PRJ-187Economic Analysis UVM

Expansion 9 months 3

Populate the FK attribute: Referential Integrity Error

Project

ProjectID ProjectName Duration Phase ManagerID

PRJ-145 Health Care Database 14 months 2 756-98-2222

PRJ-147Traveler's Insurance Payroll

System 26 months 1 756-98-2222

PRJ-151 Capital Finance Highway 41 7 months 1 123-76-8823

PRJ-187Economic Analysis UVM

Expansion 9 months 3 654-98-0033

We will end up with a referential integrity violation

Referential Integrity

Manager ID?

One of the FK attribute values in the Project Table (the M side of the relationship) does not exist in the parent table (the Manager Table – the one side of the relationship). There is NO manager ID 654-98-0033, so that ID value cannot be assigned to a project

Manager

ManagerID FirstName LastName Address Salary

765-98-2222 Dave Smith 2 Main St. $75,000

123-45-6789 Sue Jones 1 East St. $80,000

123-76-8823 Mary Wells 1 North St. $78,000

Referential Integrity and Tables The specific value you enter for any FK

attribute value must FIRST exist in the parent table (the table that relates directly to the particular attribute – in our case where the FK is a PK)Example: I cannot be assigned to teach a

section of 141 (or any other class) if I am not first listed in the professor / teacher table

You have a value for ManagerID that exists in the Manager table

Design Rules

Normalization

Design Rules

NormalizationTypically a trade-off between higher levels of

normalization and processing speedAs redundancy is reduced, the time it takes

the DBMS to process a query or extract data could increase• Higher levels of normalization may not always be

desired where processing speed is critical

Design Rules

We want to convert this single table DB file to a relational DBMS format

Proj# ProjName ProjStartDate Emp# EmpName EmpAddress JobClass HrBillRateHrs

WorkedProj

Manager15 UVM DB Design 10/15/2009 12 John Jones 14 Green St. Elect. Eng. 85 3015 UVM DB Design 10/15/2009 34 Sally Smith 14 Green St. DB Designer 100 20 Y15 UVM DB Design 10/15/2009 22 Homer Simpson 34 Blue Ave. Sys Analyst 50 4021 Health Care Evaluation 7/1/2009 12 J. Jones 14 Green St. Elect. Eng. 85 15 Y21 Health Care Evaluation 7/1/2009 35 Jill Wilson 876 Lake Rd. Programmer 60 4521 Health Care Evaluation 7/1/2009 34 Sally Smith 14 Green St. DSS Analyst 70 4021 Health Care Evaluation 7/1/2009 22 Homer Simpson 34 Blue Ave. DB Designer 90 1530 Roadway B/C 9/15/2010 34 Sally Smith 14 Green St. Economist 75 50 Y30 Roadway B/C 9/15/2010 35 Jill Wilson 876 Lake Rd. Programmer 60 75

Design Rules

There are clearly some redundancy issues with the data

How do we address redundancy via normalization and organize the data into relational tables?

Step 1

The current format is just an Excel file, not a relational DBMS

Identify attributes of each entity (or fields to be placed in each table)

Step 2 Create tables to capture data we need

We want attributes and data related to a specific entity in one table and attributes and data related to another entity in a different table

Design tables to minimize need to enter redundant information

What do we do with attributes that pertain to both employee and project?

Step 3

Consider relationship connectivity (1:M, M:M) between the entities – may be a trial and error processWhat type of relationship is needed here?

• Can employees work on more than 1 project at a time, or only 1 project at a time?

• Is each project staffed by only 1 employee, or can each project be staffed my multiple employees?

We can tell by looking at the data in the Excel table

Step 4

Draw the partial ERD