Concepts of Database Management Seventh Edition Chapter 6

Concepts of Database Management Seventh Edition Chapter 6 Database Design : ERD Model

Objectives • Discuss the general process and goals of database design • 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 2

Objectives (continued) • 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 3

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) 4

Introduction • 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 5

Building Blocks of ERD Type English Grammar Equivalent Example Entity Proper Noun Student, Employee, Instructor, Courses, Room Relationship Verb has, teaches, belongs, handles Attribute Adjective Height, Age, Gender, Nationality, First name 6

ERD Popular Notation • Chen Notation • Crow’s Foot Notation 7

Chen Notation - Symbol Rectangle represents an Entity Diamond represents a Relationship 1 M Lines with labels represents Cardinality 8

Entity (Chen Notation) • is a real-world object distinguishable or unique from other objects. • 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 etc. • It is normally represented by a rectangle shape. 9

Database Background • Remember in Chapter 1 Entity could be a : (ex. Teacher, Student, Physician) Person Place Object (ex. School, Hotel, Store ) (ex. Mouse, Books, Bulding ) Event Idea or Concept (ex. Enroll, Withdraw, Order ) (ex. Courses, Account, Delivery ) 10

Entity - Example • For example in our Premiere Database the different Entities are the following: Customer Sales Rep Order Parts 11

Relationship • 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 or nouns. • It is normally represented by a diamond shape. 12

Relationship - Example • For example in our Premiere Database again we have this relationships among entities: Sales Rep represents Customer has Could be read as : A Sales Represents a Customer. And a Customer has an Order 13

Cardinality • 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 14

Cardinality - Symbols 1 M One-is-to-many Relationship M N Many-to-many Relationship 15

Cardinality Symbols - Example 1 Sales Rep represents M Customer Could be read as : A Sales Rep could represent 1 or Many Customers. 16

Cardinality Symbols – Example (Cont’d) M Order has N Parts Could be read as : An Order could have many Parts (e. g. Products Ordered) and a Part could have many Orders. 17

Degree of Relationship • There are three Degree of Relationships in ERD notation, namely: – Unary – Binary – Ternary 18

Degree of Relationship (Cont’d) Unary Binary Ternary 19

Degree of Relationship (Cont’d) Manages Unary Employee makes Customer Orders Vendor Warehouse Binary Ternary supplies Part 20

Attribute • 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 on a certain date so you will have an attribute of Enrollment Date under Enroll relationship. • It is normally represented by an oval. 21

Attribute - Example Firstname Lastname Rep. Num Street City Sales Rep State Zip Rate Take note that a Primary Key is underlined. Commission 22

Attribute – More Example Customer. Name Firstname Customer. Num Lastname Rep. Num Street 1 City Sales Rep M Customer represents City State Zip Rate Commission Credit. Limit Zip Balance 23

Crow’s Foot notation - Symbol Entity name Attribute 1 Attribute 2 Attribute 3 Attribute 4 24

Crow’s Foot notation - Example Entity Student. ID Firstname Lastname Gender Program Attributes 25

Crow’s Foot notation - Keys Student. ID (PK) Firstname Lastname Gender Program. ID (FK) PK – Primary Key FK – Foreign Key 26

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. 27

Crow’s Foot notation – with Cardinality Customer Repnum (PK) Firstname Lastname Commission Rate Customernum(PK) Customername Street City State Zip Balance Credit. Limit Repnum (FK) 28

Non-Graded Seatwork • Using Premier Database – Create a Chen notation on at least two tables that is not part of our example and tables that has relationship – Create a Crow’s Foot notation on at least two tables that is not part of our example and tables that has relationship 29

Graded Seatwork • Create both Chen and Crow’s foot notation on all tables and relationship – Alexamara Marina – Henry Books 30

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