1. Entity-Relationship Model and Diagrams (continued)
Todd S. Bacastow
IST 210
Organization of data

2. Database Design Conceptual design Logical design Physical design
Entity-Relationship Model
Logical design
Logical Schema
Physical design

3. Critical Success Factors in Database Design
Work interactively with the users as much as possible
Follow a methodology throughout the data modeling process
Incorporate structural and integrity considerations into the data models
Combine conceptualization, normalization, and validation techniques into the methodology

4. Conceptual Design Phase

5. ERD as a “Semantic Model”
Semantics: Relationships between symbols and their meanings.
A semantic model attempts to capture the meaning of user's information and provide a concise, high-level description of that information.
The information is represented by logical associations (relations) between pairs of objects and by the classification of objects into categories (entities).

6. Entity, Attribute, Relationship
Name
Address
Numb
CLIENT
PASSPORT
Exp
A client must have a passport
Each client has only one passport
A client may have one or more itinerates
An itinerary belongs to one client
ITINERARY
Date
city

7. Basic relationships One-to-One One-to-Many Many-to-Many
HUSBAND
WIFE
A husband has one wife
A wife has one husband
One-to-Many
TEAM
PARTICIPANT
A team has many participants
Many participants belong to one team
Many-to-Many
EMPLOYEE
SKILL
An employee has many skills
Many employees have the same skill

8. Exercise
Business rules: A university where a student may take many courses employs lecturers. Each lecturer teaches one or more courses but no course is taught by more than one lecturer. Each student has to complete two or three assignments for each course.
Requirement: Draw an entity relationship (ER) diagram for the situation described.

9. Solution

10. Review Use ER Diagrams to help understand The essential information
Visual guide to the organization
Plan for how to proceed
Improve database design

11. Logical design phase Conceptual E-R Model
1. REFINE THE CONCEPTUAL MODEL
Refined Conceptual Model
2.APPLY THE RULES OF NORMALIZATION
Logical
Data
Model

12. The Next Step Going from this: To this: Table1 Table2 Table3 Table4

13. Logical Database Design
Main objectives of relational databases is to ensure that each item of data is held only once within the database:
Minimize the amount of storage space
Simplify updating procedures
Ensure that data is accurate
Done by converting ERD into well-structured relational data model

14. Relational Data Model E-R Model helps to define the underlying tables
CUSTOMER
CUSTOMER
receive
INVOICE
INVOICE

15. Converting ERD to tables
Convert each of the entities (E1 & E2) in to a table. The attributes of the entity become attributes of the table.
Convert each relationship (R1) with a many-to-many cardinality in to a table. The primary keys of the entities (E1 & E2) linked by the relationship and attributes of the relationship A1 become attributes of the resulting table.
Do not convert relationships (R1) with one-to-many or one-to-one cardinality in to a table.
For a one-to-one relationship, add the attributes of the relationship (A1) and the primary key of either table (T1 or T2) into the other table (T1 or T2).
For a one-to-many relationship, add the attributes of the relationship (A1) and the primary key to the other table.
Relationship1 R1
Entity 1 E1
Entity 2 E2 A1

16. Fields and Records Field: a single column of information in a table
Appears as an attribute in the ERD
Key: a field which uniquely identifies each record in a field
Field
Key

17. Fields and Records
Foreign Key
Foreign Key: links tables by referencing a key in another table
Tuple: the full set of information about one occurrence of the entity
All information included in a single row of the table
Tuple

18. Review The key conversion tasks are: Create entity tables
Resolve relationships
Resolve multi-valued and composite attributes
Insert primary and foreign keys
Normalize to Third Normal Form (we will talk about this next time)
Integrity constraints

19. Review Relations Just another name for a table
Every relation has a unique name
Every attribute value is atomic
Every row is unique
Attributes in tables have unique names
The order of the columns is irrelevant
The order of the rows is irrelevant