1. Entity-Relationship (ER) Modeling

2. Database Design Process
Application 1
Application 2
Application 3
Application 4
External
Model
External
Model
External
Model
External
Model
Application 1
Conceptual
requirements
Application 2
Conceptual
requirements
Conceptual
Model
Logical
Model
Internal Model
Application 3
Conceptual
requirements
Application 4
Conceptual
requirements

3. Stages in Database Design
Requirements formulation and analysis
Conceptual Design -- Conceptual Model
Implementation Design -- Logical Model
Physical Design --Physical Model

4. Database Design Process
Requirements formulation and analysis
Purpose: Identify and describe the data that are used by the organization
Results: Metadata identified, Data Dictionary, Conceptual Model-- ER diagram

5. Database Design Process
Requirements Formulation and analysis
Systems Analysis Process
Examine all of the information sources used in existing applications
Identify the characteristics of each data element
numeric
text
date/time
etc.
Examine the tasks carried out using the information
Examine results or reports created using the information

6. Conceptual Modeling Objective: to produce HIGH-LEVEL DATA MODEL GOALS
a complete understanding of the database structure, meaning (semantics), interrelationships, and constraints
A stable description of the database contents
Usually more expressive and general than data models of individual DBMSs
Vehicle of communication among database users, designers, and analysts.

7. Database Design Process
Conceptual Model
Merge the collective needs of all applications
Determine what Entities are being used
Some object about which information is to maintained
What are the Attributes of those entities?
Properties or characteristics of the entity
What attributes uniquely identify the entity
What are the Relationships between entities
How the entities interact with each other?

8. Database Design Process
Logical Model
How is each entity and relationship represented in the Data Model of the DBMS
Hierarchic?
Network?
Relational?
Object-Oriented?

9. Database Design Process
Physical ( Internal) Model
Choices of index file structure
Choices of data storage formats
Choices of disk layout

10. Database Design Process
External Model
User views of the integrated database
Making the old (or updated) applications work with the new database design

11. Data Models: History Relational Model (1980’s)
Provides a conceptually simple model for data as relations (typically considered “tables”) with all data visible.

12. Data Models: History Object Oriented Data Model (1990’s)
Encapsulates data and operations as “Objects”
Books
(id, title)
Publisher
Subjects
Authors
(first, last)

13. Intro. to ER Models
Entity/Relationship approach - one of the most well known modeling methods
Developed by P.Chen in many variations since then
Data modeling is generally considered the most important component of the systems development process

14. Entity Relationship Diagrams
A Simple ERD:
 Consider the following situation
A customer places an order. The order consists of parts.
Entity
Relationship
Another Relationship
Places
Contain
Customer
Orders
Parts
An Organization about which we wish to maintain information
An Association between Entities
Another Entity
Altogether, a Database

15. ER NOTATION Attribute Entity type Key attribute Weak entity type
Multivalued attribute
Relationship type
Derived attribute
Identifying
Relationship type
Composite attribute

16. A special entity that is also a relationship
Relationship symbols
Entity symbols
Attribute symbols
A special entity that is also a relationship
Relationship degrees specify number of entity types involved
Relationship cardinalities specify how many of each entity type is allowed 8

17. Entity
An Entity is an object in the real world (or even imaginary worlds) about which we want or need to maintain information
Persons (e.g.: customers in a business, employees, authors)
Things (e.g.: purchase orders, meetings, parts, companies)
Employee

18. Inappropriate entities
Figure 3-4
System output
System user
Appropriate entities

19. Identifiers (Keys)
Identifier (Key) - An attribute (or combination of attributes) that uniquely identifies individual instances of an entity type
Simple Key versus Composite Key
Candidate Key – an attribute that could be a key…satisfies the requirements for being a key 6

20. Characteristics of Identifiers
Will not change in value
Will not be null
No intelligent identifiers (e.g. containing locations or people that might change) 7

21. Attributes
Attributes are the significant properties or characteristics of an entity that help identify it and provide the information needed to interact with it or use it. (This is the Metadata for the entities.)
Employee
Last
Middle
First
Name
SSN
Age
Birthdate
Projects

22. Figure 3-7 – A composite attribute
An attribute broken into component parts 12

23. Weak Entities Owe existence entirely to another entity Order-line
Contains
Order
Invoice #
Part#
Rep#
Quantity
Invoice#

24. Figure 3-9a – Simple key attribute
The key is underlined 14

25. Figure 3-9b – Composite key attribute
The key is composed
of two subparts 15

26. Figure 3-8 – Entity with a multivalued attribute (Skill) and derived attribute (Years_Employed)
What’s wrong with this?
Derived
from date employed and current date
Multivalued:
an employee can have
more than one skill 13

27. Relationships
Relationships are the associations between entities. They can involve one or more entities and belong to particular relationship types

28. Relationships Class Attends Student Part Supplier Project Supplies

29. Relationships Class Attends Student Part Supplier Project Supplies

30. Types of Relationships
Concerned only with cardinality of relationship
Truck
Assigned
Employee
Project 1 n m
Chen ER notation

31. Other Notations “Crow’s Foot” Truck Employee Project Employee Project
Assigned
Employee
Project
Assigned
Employee
Project
Assigned
Employee
“Crow’s Foot”

32. Degree of Relationships
Degree of a relationship is the number of entity types that participate in it
Unary Relationship
Binary Relationship
Ternary Relationship 16

33. Degree of relationships – from Figure 3-2
Entities of two different types related to each other
One entity related to another of the same entity type
Entities of three different types related to each other 8

34. Cardinality of Relationships
One-to-One
Each entity in the relationship will have exactly one related entity
One-to-Many
An entity on one side of the relationship can have many related entities, but an entity on the other side will have a maximum of one related entity
Many-to-Many
Entities on both sides of the relationship can have many related entities on the other side

35. Cardinality Constraints
Cardinality Constraints - the number of instances of one entity that can or must be associated with each instance of another entity
Minimum Cardinality
If zero, then optional
If one or more, then mandatory
Maximum Cardinality
The maximum number 29

36. 22

37. 23