1. Entity Relationship Diagrams

2. Supplier Item Production Shipment Plan Master Product Schedule
Mandatory 1
Sends
Supplier
Mandatory many
Optional many
Supplies
Many with maximum
Sent by
Supplied by
Includes
Item
Shipment
Produces
Production
Plan
Produced on
Included on
Goes into
Generated on
Composed of
Generates
Product
Builds
Master
Schedule
Built on

3. Entity Relationship Diagrams
Purpose: Show the structure (relationship of data elements)
Can be used in multiple stages of development
Used to communicate and verify understanding between developers and users, and to document the perceived data model

4. ERD Elements Entities Relationships Identifiers Attributes
Things about which you collect information
Relationships
Means of association between entities
Identifiers
Unique attributes of the entity
Attributes
Characteristic or property of the entity that is of interest

5. ERD Symbols Entities: rectangle
Relationships: diamond (may or may not be used), on a line showing the “cardinality” of the relationship (1 to many), etc.
Identifiers: Underlined text
Attributes: Text by the entity (if shown at all on the diagram)

6. Sample ERDs Order Part Supplier Entity attributes: ORDER 1 CAN HAVE 1
ORDER: #, DATE, PART #, QUANTITY
PART: #, DESCRIPTION, UNIT PRICE, SUPPLIER #
SUPPLIER: #, NAME, ADDRESS
Order 1
CAN HAVE 1
Part
PART M
CAN HAVE 1
Supplier
SUPPLIER

7. ERD Notes Relationship connect entities
Attributes are not technically a part of the diagram but are often included
ERD is not the same as a relational table design

8. Entity Sets
Each individual object is called an entity. A collection of such entities is an entity set.
Example: Joe, Jill, and Mary represent entities. They are all ascribed to the entity set, PERSON.
Example: A collection of projects is the project entity set.

9. Relationship Relationship Relationship set
One interaction between one or more entities
For example: if a person works on a project, there is a relationship between that person and the project
Relationship set
A collection of such relationships.
A component in an E-R diagram that represents a set of relationships with the same properties.

10. Notes on Entities and Relationships
We can actually see entities, but we cannot see relationships.
For example:
Entity sets: Person; project
Relationship: People work on projects. This becomes the relationship set “Work”
Persons
The set of people, set of projects and
set of working relationships.
Work
Projects

11. Entity-Relationship Structures
Persons are in departments
Persons work on projects
Persons
Parts
Supply
Suppliers
Projects use parts
Suppliers supply parts
Warehouses hold parts
Hold
Are-In
Work-On
Use
Warehouses
More complex relationship:
See persons and parts
Depts
Projects

12. Entities can have multiple relationships
Companies
Leases
Owns
Vehicles

13. More than two entity sets can be associated with the same relationship set
Relationship sets that include only two
entities are known as binary. More than
two are known as N-ary.
Customers
Buy
Stores
Each relationship in this set includes a person, a part bought
by the person, and the store where the purchase was made.
Parts
A person, a part bought by the person,
and the store where the purchase was made

14. Identifiers
One of the attributes of an entity or relationship set is called the identifier
It has one important property: its values identify unique entities in the entity set.

15. Identifiers are underlined here
PERSON-ID
NAME
ADDRESS
PROJECT-ID
TIME-SPENT
START-DATE
BUDGET
Persons
Work
Projects
The set of people, set of projects and
set of working relationships.

16. Convention for Identifiers in Relationships
Use the identifiers of the entities that participate in the relationship as the relationship identifiers.
Identifiers are not file keys here. At this stage, they are the identifiers of entities that participate in the relationship.

17. Cardinality
The number of relationships in which one entity can appear.
An entity can appear in:
one (1) relationship;
any variable number (N) of relationships; and
a maximum number of relationships

18. Cardinality - Example Persons N Work M Projects
PERSON-ID
NAME
ADDRESS
PROJECT-ID
TIME-SPENT
START-DATE
BUDGET
Persons N
A persona can appear in more than one
WORK relationship, and so can a project.
If there was a limit to the number of times an
entity can take part in the relationship, then
N or M would be replaced by the actual
maximum number.
Work M
Projects
The set of people, set of projects and
set of working relationships.

19. Cardinality - Example Manager 1 Manage N Projects
MANAGER-ID
NAME
ADDRESS
PERSON-ID
PROJECT-ID
TIME-SPENT
START-DATE
BUDGET
Manager 1
Here a project has one (1) manager, whereas
a manager can manage any number (N) of
projects.
Manage N
Projects
The set of people, set of projects and
set of working relationships.

20. Cardinality - Example Manager 1 Manage N Projects
MANAGER-ID
NAME
ADDRESS
PERSON-ID
PROJECT-ID
TIME-SPENT
START-DATE
BUDGET
Manager 1
The denotes optional participation on the
project. If it is mandatory, then there is no
placed there.
Manage N
Projects
The set of people, set of projects and
set of working relationships.

21. Issues in building an ER-Diagram
How to choose entities, relationships and attributes
How to choose names
What steps should be followed

22. Choosing Attributes
Attributes, just like entity and relationship sets, should express simple concepts.
E-R diagrams should not contain multi-valued or structured attributes
For example:
PERSON-ID
DATE-OF-BIRTH
QULIFICATION* (asterisk means it is multivalued-repeating)
ADDRESS
(NUMBER, STREET, SUBURB)
PERSONS
Non-simple attributes
Addresses has structured attributes.
These should be replaced in the final diagram
by relationships.

23. Ex: Removing multi-valued and structured attributes
PERSON-ID
DATE-OF-BIRTH
Persons
PERSON-ID
QUALIFICATION
HAVE
LIVE-AT
PERSON-ID
NUMBER
STREET
SUBURB
QUALIFICATION
NUMBER
STREET
SUBURB
QUALIFICATIONS
ADDRESSES

24. Choosing Object Set Names
Remember, that one goal of E-R modeling is to produce a model that is easily understood by users as well as computer personnel.
Entity sets are labeled as nouns
Relationship sets are labeled by verbs
Relationship sets are structured as prepositions when modeling structural relationships

25. Where to begin Start with entity sets
Look at how entities interact with each other and model this in terms of relationship sets
Then add cardinality to the system
Add attributes and choose identifiers

26. Normalization Highlights

27. Normalization
The process of organizing data in a database. This includes creating tables and establishing relationships between those tables according to rules designed both to protect the data and to make the database more flexible by eliminating two factors: redundancy and inconsistent dependency.

28. Factor 1: Inconsistent Dependency
Customer table should have customer address but not employee salary who calls on customer
If customer information is contained in an order file, if the order is canceled, all the customer information could be lost
Solution: create two tables--one table contains order information and the other table contains customer information.

29. Factor 2: Redundant Data
Data exists in more than one place
Wastes disk space and creates maintenance problems
Example: a staff person changes their telephone number and every potential customer that person ever worked with has to have the corrected number inserted.

30. Rules for Database Normalization
First Normal Form
No repeating groups
Second Normal Form
Eliminate data redundancy
Third Normal Form:
Eliminate data not dependent on key

31. Database Normalization - Example
DMOD
ISDATAD
STARTING WITH A SET OF DATA ITEMS:
Employee Name
Employee ID
Department
Dept Address
Item#
Item Description
Item Price
Warehouse ID
Warehouse Address
Item Location in each Warehouse
Quantity on Hand in each Warehouse

32. Database Normalization - Example
DMOD
ISDATAD
1. CLUSTER DATA ITEMS INTO ENTITIES (to become TABLES):
Employee ID
Employee Name
Department
Dept Address
Item#
Item Description
Item Price
Warehouse ID
Warehouse Address
Item Location in each Warehouse
Quantity on Hand in each Warehouse

33. Database Normalization - Example
DMOD
ISDATAD
2. PULL OUT MULTI-VALUED ITEMS or REPEATING GROUPS:
From:
Item# Description Price
WarehouseID Address ItemLocation Quantity on Hand
To:
Item# Description Price
Item# Warehouse ID Address ItemLocation Quantity on Hand
NOTE: Item# propagates down and becomes part of the identifier. Why?

34. Database Normalization - Example
DMOD
ISDATAD
3. PULL OUT FACTS ABOUT A PORTION OF THE KEY (partial dependency):
From:
Item# Description Price
Item# Warehouse ID Address Item Location Quantity on Hand
To:
Item# Description Price
Item# Warehouse ID Item Location Quantity on Hand
Warehouse ID Address

35. Database Normalization - Example
DMOD
ISDATAD
4. PULL OUT FACTS ABOUT A NON-KEY DATA ITEM (transitive dependency):
From:
Employee ID Employee Name Department Dept Address
To:
Employee ID Employee Name Department
Department ID Dept Address
What is the “Department” field called in the Employee record?
Why does it remain in the Employee record?

36. Role of data values Table components Fields vs. values
Records are related via the values
Customer table
Order table
Relation by
data value