Concepts of Database Management
Database Design : ERD Model
• Discuss the general process and goals of database
• Identify the different symbols used in ERD
• Identify cardinality symbols to used for different
entity relationship types
• Create an entity-relationship (E-R) diagram to
visually represent a database design
• Explain the physical-level design process
• Discuss top-down and bottom-up approaches to
database design and examine the advantages and
disadvantages of both methods
• Use a survey form to obtain information from users
prior to beginning the database design process
• Review existing documents to obtain information
prior to beginning the database design
The Entity-Relationship Model
• is modeling tool used to depict graphically a
database design before it is actually implemented.
• It has three basic components, namely, an Entity,
Relationship and an Attribute.
• And Relationship has Cardinality (as we will see
more in a moment)
• Two-step process for database design
• Information-level design: completed
independently of any particular DBMS
• Physical-level design: information-level design
adapted for the specific DBMS that will be used
– Must consider characteristics of the particular DBMS
Building Blocks of ERD
English Grammar Equivalent
Height, Age, Gender,
ERD Popular Notation
• Chen Notation
• Crow’s Foot Notation
Chen Notation - Symbol
Rectangle represents an Entity
Diamond represents a Relationship
Lines with labels represents Cardinality
Entity (Chen Notation)
• is a real-world object distinguishable or unique from
• An entity can be a concrete or physical object like
employee, student, faculty, customer etc. Or it could
also be conceptual or abstract like transaction, order,
course, subjects etc.
• It can be thought of as a noun like student, employee
• It is normally represented by a rectangle shape.
• Remember in Chapter 1 Entity could be a :
(ex. Teacher, Student, Physician)
(ex. School, Hotel, Store )
(ex. Mouse, Books, Bulding )
Idea or Concept
(ex. Enroll, Withdraw, Order )
(ex. Courses, Account, Delivery )
Entity - Example
• For example in our Premiere Database the different
Entities are the following:
• is a way of relating one entity to another. Entities can
therefore participate in a relationship.
• it is commonly thought as a verb connecting the entities
• It is normally represented by a diamond shape.
Relationship - Example
• For example in our Premiere Database again we have
this relationships among entities:
Could be read as : A Sales Rep
Represents a Customer. And a
Customer has an Order.
• Cardinality: number of items that must be included
in a relationship
– An entity in a relationship with minimum cardinality
of zero plays an optional role in the relationship
– An entity with a minimum cardinality of one plays a
mandatory role in the relationship
Cardinality - Symbols
Cardinality Symbols - Example
Could be read as : A Sales Rep could represent
1 or Many Customers.
Cardinality Symbols – Example
Could be read as : An Order could have many Parts (e.g. Products
Ordered) and a Part could have many Orders.
Degree of Relationship
• There are three Degree of Relationships in ERD
Degree of Relationship (Cont’d)
Degree of Relationship (Cont’d)
• Refers to the characteristic or basic fact or field of an
Entity or Relationship.
• For example a Student entity could have the following
attributes ID Number, Last Name, First Name,
Address, Birth Date etc.
• A relationship could also have an attribute for example
an Entity name Student enrolls (relationship) to a
Course/Program. Now, when you enroll you enroll on
a certain date so you will have an attribute of
Enrollment Date under Enroll relationship.
• It is normally represented by an oval.
Attribute - Example
Take note that
a Primary Key
Attribute – More Example
Crow’s Foot notation - Symbol
Crow’s Foot notation - Example
Crow’s Foot notation - Keys
PK – Primary Key
FK – Foreign Key
Crow’s Foot Cardinality - Symbols
One and only one included in the relationship
Zero or many could be included in the relationship.
This is optional mode.
One or many could be included in the relationship.
This is mandatory mode.
Crow’s Foot notation – with Cardinality
• Using Premier Database
– Create a Chen notation on at least two tables that is
not part of our example and tables that has
– Create a Crow’s Foot notation on at least two tables
that is not part of our example and tables that has
• Create both Chen and Crow’s foot notation on all tables
– Alexamara Marina
– Henry Books