1. Entity Relationship Diagrams and Relational DBs
BSAD 141
Dave Novak

2. Topics Covered ERD (entity relationship diagram) Data Modeling
Entity –vs- Entity set
Attribute –vs- Relationship
Types of attributes and their domain
Characteristics of relationships
Degree
Connectivity
Existence

3. Modeling
Why would it be necessary or useful to model the structure of a database system?
Before spending time and money on implementation:
Make sure structure of DB is logical and technically correct
Make sure structure addresses needs and constraints of data collection and use
Make sure structure helps supports organization’s information needs

4. Modeling Data Model Entity-Relationship Diagram (ERD)
Popular model that focuses on data

5. ERD
ERD: Graphical “blueprint” for the exact design and structure of a relational DB
Shows details of things organization collects data about and how those things are related

6. Relational Database Management System RDBMS
A very popular, widely used DBMS
Made possible by modern computing power –computer must a lot of processing work
User does not need to understand the underlying structure of the database
Based on SQL

7. Relational Databases
Organization of data in two-dimensional tables connected via relationships
Tables are “linked” to one another using a common data element (attribute) that appears in both tables
By linking tables via relationships users can navigate the database and extract and combine data from different tables

8. Relational Databases
The Table is the fundamental component in a relational database
All data belong to a table
This approach provides a much easier way to manage data
Data are essentially “grouped” by common themes and then connected by relationships in a logical manner based on the ERD

9. Relational Databases
A relationship is a connection between two or more simple two-dimensional tables that consist of rows (entity / records) and columns (attributes / fields) of data

10. Relational Databases Each entity is a unique observation
Each row in a table
Attributes are the common characteristics that are used to describe the entities in the table
The columns in each table

11. Relational Databases
Power of an RDBs comes from ability to quickly find and bring together data stored in separate tables using queries, forms, and reports
Can bring together attributes and entities from separate tables

12. Relational Databases
CLASS SECTION Table

13. Review What is the entity set represented here?
What is an example of an entity within the entity set?
What are some of the attributes of the entity?
Why is the first field – Employee ID – underlined?

14. Review Key Terminology
Entity Set / Table (has a name that directly relates to the primary information stored in the table)
Entity / Record (this is a row in a table)
Attribute / Field (this is a column in the table that describes a characteristic of the entity)
Relationship (an association or linkage between two (+) tables)

15. Primary Keys
Each record/entity must have a attribute (field/column) or set of attributes that uniquely identifies that specific entity from all the other entities stored in the table
The unique attribute (or set of attributes) is called the primary key

16. Primary Keys For our purposes:
ALL relational DB tables must have a primary key
ALL entities within the table must have a unique primary key value
The primary can be created by you
Doesn’t have to provide value-added information
Can be a combination of fields/attributes
Can be sequential numbers
Can be a combination of letters and numbers
Cannot be repeated or left blank for an entity

17. Different Types of Attributes
Simple –vs- composite
Single valued –vs- multi-valued

18. Attribute Domain
The collection or range of all possible allowable values an attribute may take on
EmpDOB: list of all valid employee birth
NumDependents: positive integers from 0 to 15
Height: positive real numbers between 36.0 and 84.0 inches.
UnionMember: logical yes (true) or no (false)
EmpSSN: list of valid social security numbers

19. Value for Each Attribute
Each data attribute takes on a specific value:
A value is one particular instance of an allowable attribute for an entity
e.g. Employee attributes:
EmpSSN
EmpDOB
NumDependents
Unionmember
Height

20. Relationships Entities are connected to one another via relationships
The association between two or more entities
How we connect the entities or rows in one table to the entities or rows in another table

21. Relationships 3 important characteristics of relationships: 1) Degree
2) Connectivity
3) Existence

22. Relationship Degree
Loosely equal to the number of entities involved in a particular relationship
Could also view this more simplistically as the number of tables “linked” by each relationship
1= Unary (aka recursive)
2= Binary
3= Ternary

23. Relationship Connectivity
Three types of connectivity relationships are used to describe associations between the entities in different tables
How are entities logically connected in the DB?
1) One-to-Many
2) Many-to-Many
3) One-to-One

24. Relationship Connectivity
Why does this matter?
Logically the relationship needs to make sense
Don’t want the database functionality to allow relationships that are not feasible or practical
From a practical perspective, the foreign key always goes on the many side of the relationship – need to get this correct
Special implementation of M:M & 1:1

25. Relationship Connectivity
1:1
Employee
Vehicle
Company
Vehicle #1
Vehicle #2
Vehicle #3
Employee #1
Employee #2
Employee #3 1 1
This relationship connectivity shows that each employee can be associated with only one company vehicle and that each company vehicle can be associated with only one employee.
In this case, the RDB will be structured in a manner that matches a specific employee to a specific company car each and every day. Each car would be explicitly linked to a particular employee

26. Relationship Connectivity
One-to-One relationship
Employee is assigned to one Company Car
Each Company Car is assigned to only one employee

27. Relationship Connectivity
1:M
Employee
Department
Accounting
Department
Human
Resources
Dept
Employee #1
Employee #2
Employee #3
Employee #4 M 1
This relationship connectivity shows that each employee can be associated with
only one organizational department (employees cannot simultaneously be
assigned to, or work in, two different departments). However, each department
can be staffed with many / multiple employees

28. Relationship Connectivity
One-to-Many relationship
A professor can teach many different class sections
Each class section is taught by only one professor
A customer account can contain many invoices
Each invoice is associated with only one customer account

29. Relationship Connectivity
One-to-Many example
Relationship is labeled 1:M
Each
teaches M
Class
Section
Professor 1
Each is
taught by
Read: left to right on the top of the line
Read: right to left on the bottom of the line

30. Relationship Connectivity
M:M
Customer
Product
Product #1
Product #2
Product #3
Product #4
Customer #1
Customer #2
Customer #3 M M
This relationship connectivity shows that customer can be associated with many
different products and that each product can be associated with many different
customers
This relationship will be modeled in a special way!!

31. Relationship Connectivity
Many-to-Many relationship
Employee has many job skills
Each job skill can be learned by many employees
Student can take many class section
Each class section can be taken by many students

32. Relationship Existence
Denotes whether participation in a relationship is required (or not), and the minimum and maximum number of entities that participate in a particular relationship
Mandatory: The existence of one entity depends on the existence of another entity
Optional: The existence of one entity is independent of the existence of another entity

33. Mandatory Relationship Existence Example
Employee
Department
Accounting
Department
Human
Resources
Dept
Employee #1
Employee #2
Employee #3
Employee #4
The existence of an instance of employee (an individual employee) depends on the existence of a department where the employee will be assigned
In this case, the entity set Department will need to be populated before the entity set Employee is populated

34. Optional Relationship Existence Example
Employee
Department
Accounting
Department
Human
Resources
Dept
Employee #1
Employee #2
Employee #3
Employee #4
The existence of an instance of employee (an individual employee) is independent of the existence of a department where the employee will be assigned
In this case, the entity instance employee #4 can be created without the need to assign that employee to a department

35. Relationship Existence Example
Course Section
Course
BSAD 141
BSAD 173
BSAD 120
CRN 5099
CRN 5060
CRN 5061
CRN 5062
Discuss…

36. Investigating Relationships
1:M relationship
This relationship states that each supplier can provide
(or distributes) many different products (1, 2, … n), but each
of those products is provided by (or distributed by) only one
supplier
In this case, the structure would not allow a specific product
to be provided by (or distributed by) to more than one supplier
Supplier
Product
Can provide M
Is provided by 1

37. Investigating Relationships
1:M relationship
Nike produces and distributes many models of shoe that
are unique to Nike
Adidas produces and distributes many models of shoe that
are unique to Adidas
ASICS produces and distributes many models of shoe that
are unique to ASICS
Supplier
Product
Can provide M
Is provided by 1

38. Supplier Table Can provide M Supplier Product 1 Is provided by
Supplier ID
Company Name
Contact Name
Contact Title
Address
City
Region
Postal Code
Country
Phone 2
New Orleans Cajun Delights
Shelley Burke
Order Administrator
P.O. Box 78934
New Orleans LA
70117
USA
(100) 3
Grandma Kelly's Homestead
Regina Murphy
Sales Representative
707 Oxford Rd.
Ann Arbor MI
48104
(313) 16
Bigfoot Breweries
Cheryl Saylor
Regional Account Rep.
th Avenue Suite 210
Bend OR
97101
(503)

39. Product Table Can provide M Supplier Product 1 Is provided by
Product ID
Product Name
Supplier ID
Category
Quantity Per Unit
Unit Price
Units In Stock
Units On Order
Reorder Level 7
Uncle Bob's Organic Dried Pears 3
Seafood
lb pkgs.
$30.00 15 10 8
Northwoods Cranberry Sauce
Condiments
oz jars
$40.00 6 4
Chef Anton's Cajun Seasoning 2
oz jars
$22.00 53 5
Chef Anton's Gumbo Mix
36 boxes
$21.35 34
Sasquatch Ale 16
Beverages
oz bottles
$14.00
111 35
Steeleye Stout
$18.00 20 65
Louisiana Fiery Hot Pepper Sauce
oz bottles
$21.05 76 66
Louisiana Hot Spiced Okra
oz jars
$17.00
100

40. Product Table
Product ID
Product Name
Supplier ID
Category
Quantity Per Unit
Unit Price
Units In Stock
Units On Order
Reorder Level 7
Uncle Bob's Organic Dried Pears 3
Seafood
lb pkgs.
$30.00 15 10 8
Northwoods Cranberry Sauce
Condiments
oz jars
$40.00 6 4
Chef Anton's Cajun Seasoning 2
oz jars
$22.00 53 5
Chef Anton's Gumbo Mix
36 boxes
$21.35 34
Sasquatch Ale 16
Beverages
oz bottles
$14.00
111 35
Steeleye Stout
$18.00 20 65
Louisiana Fiery Hot Pepper Sauce
oz bottles
$21.05 76 66
Louisiana Hot Spiced Okra
oz jars
$17.00
100
Notice that SupplierID is not an attribute of Product – it is the PK of the Supplier
table and will be the FK (to the Supplier table) in the Product table

41. Uncle Bob's Organic Dried Pears 3 Seafood 12 - 1 lb pkgs. $30.00 15 10
Supplier ID
Company Name
Contact Name
Contact Title
Address
City
Region
Postal Code
Country
Phone 2
New Orleans Cajun Delights
Shelley Burke
Order Administrator
P.O. Box 78934
New Orleans LA
70117
USA
(100) 3
Grandma Kelly's Homestead
Regina Murphy
Sales Representative
707 Oxford Rd.
Ann Arbor MI
48104
(313) 16
Bigfoot Breweries
Cheryl Saylor
Regional Account Rep.
th Avenue Suite 210
Bend OR
97101
(503)
Product ID
Product Name
Supplier ID
Category
Quantity Per Unit
Unit Price
Units In Stock
Units On Order
Reorder Level 7
Uncle Bob's Organic Dried Pears 3
Seafood
lb pkgs.
$30.00 15 10 8
Northwoods Cranberry Sauce
Condiments
oz jars
$40.00 6 4
Chef Anton's Cajun Seasoning 2
oz jars
$22.00 53 5
Chef Anton's Gumbo Mix
36 boxes
$21.35 34
Sasquatch Ale 16
Beverages
oz bottles
$14.00
111 35
Steeleye Stout
$18.00 20 65
Louisiana Fiery Hot Pepper Sauce
oz bottles
$21.05 76 66
Louisiana Hot Spiced Okra
oz jars
$17.00
100

42. Investigating Relationships
The 1:M relationship example
The Supplier ID attribute in the Product table is a foreign key that links the individual products in the Product table to a specific supplier in the Supplier table

43. Summary Describe the differences between ERDs and DFDs
Describe importance of relational DBs
Familiar with all terminology: tables, relationships, entities, attributes, keys, etc
Understand how to implement a relationship
Discuss / define the 3 characteristics of relationships