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 6 TypeEnglish Grammar EquivalentExample EntityProper NounStudent, Employee, Instructor, Courses, Room RelationshipVerbhas, teaches, belongs, handles AttributeAdjectiveHeight, Age, Gender, Nationality, First name

ERD Popular Notation Chen Notation Crow’s Foot Notation 7

Chen Notation - Symbol 8 1M 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 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 : 10 Person Place (ex. Teacher, Student, Physician) (ex. School, Hotel, Store ) Object (ex. Mouse, Books, Bulding ) Event (ex. Enroll, Withdraw, Order ) Idea or Concept (ex. Courses, Account, Delivery )

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

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: 13 represents Customer Sales Rep Order has Could be read as : A Sales Rep Represents a Customer. And a Customer has an Order.

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 15 One-is-to-many Relationship 1M MN Many-to-many Relationship

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

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

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

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

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

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

Attribute – More Example 23 RepNum Sales Rep Lastname Firstname Street City State Zip Commission Rate Customer represents CustomerNum CustomerName CreditLimit Balance Street City State Zip 1M

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

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

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

Crow’s Foot Cardinality - Symbols 27 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 28 Rep Repnum (PK) Firstname Lastname Commission Rate Customer Customernum(PK) Customername Street City State Zip Balance CreditLimit Repnum (FK)

Non-Graded Seatwork 29 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

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

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