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Entity Relationship Model in Database Design

Entity Relationship Model in Database Design. BSE (A,B), MCS-I. Overview. Entity Relationship Modeling Data modeling using Entity Relationship Diagram (ERD) Transforming ERD into tables. Introduction. Design is a process Analysis Requirements (user view) Conceptual modeling (ERD)

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Entity Relationship Model in Database Design

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  1. Entity Relationship Model in Database Design BSE (A,B), MCS-I

  2. Overview • Entity Relationship Modeling • Data modeling using Entity Relationship Diagram (ERD) • Transforming ERD into tables

  3. Introduction • Design is a process • Analysis • Requirements (user view) • Conceptual modeling (ERD) • (Logical) design • Transforming ERD to tables and keys • Physical design and implementation • Using MS Access

  4. Entity-Relationship Model • A model to represent the real world • Elements • Entities • Attributes • Identifiers • Relationships

  5. Entity • Entity • Anything in the real world • Entity class (entity set) • A set of things of the same type • Entity instance • An exact instance of an entity class • ERD notation for entity • A rectangular box Books

  6. Title ISBN Books Price Attribute and Identifier • Attribute • Properties of entity • Notation: an oval • Identifier • An attribute with unique value to identify each instance

  7. Books Publishers publish Relationship • Notation: a diamond • Degree of relationship • Unary (recursive) – only 1 entity • Binary – 2 entities • Ternary – 3 entities • N-ary – more entities

  8. Governors States govern Types of Binary Relationship • One-to-One (1:1) • A single entity instance in one entity class is related to a single entity instance in another entity class • Examples: • Governors : States • Students : PantherCards • ER Notation (Crow’s foot)

  9. Types of Binary Relationship • One-to-Many (1:N) • A single entity instance in one entity class (parent) is related to multiple entity instances in another entity class (child) • Examples • Customers : Orders • Students : Degrees • ER Notation(Crow’s foot) Books Publishers publish

  10. Types of Binary Relationship • Many-to-Many (N:M) • Each entity instance in one entity class is related to multiple entity instances in another entity class; and vice versa • Examples • Books : Writers • Customers : Banking Accounts • ER Notation (Crow’s foot) Books Authors write

  11. A Complete ER Example

  12. ER Diagram Exercise • Draw a ERD about movie data • Let’s only consider the following entities and their attributes • Perfomers (Actors/Actresses): PerformerID, FirstName, LastName, Gender • Movies: MovieID, Title, Maker, Year • MovieMakers (companies): MakerID, Name • Assumptions • A movie one or more actors/actresses • An actor/actress can be in multiple movies • A movie is made by only one company

  13. Transforming ER to Tables • Guidelines to create tables • Each entity becomes a relation (table) • Attributes of the entity become fields of that table • Identifier becomes primary key • Rules to transform relationships • Based on the type of the relationship • One-to-One • One-to-Many • Many-to-Many

  14. Locker Employee LockerID EmpID Primary Key LockerDesc LockerID Foreign Key EmpName Location Transforming 1:1 Relationships • One-to-One • The key from one relation is placed in the other as a foreign key

  15. Locker Employee LockerID EmpID Primary Key EmpID EmpName Foreign Key LockerDesc Location Transforming 1:1 Relationships • Usually, it does not matter which table receives the foreign key

  16. Transforming 1:N Relationships • One-to-Many • The primary key from the “One” side is placed in the “Many” side as a foreign key • The foreign key is always on the “Many” side TaughtBy

  17. Department Employee DeptID EmpID Primary Key DeptName Dept Foreign Key EmpName Location Transforming 1:N Relationships • Another example Department Employee has

  18. Transforming N:M Relationships • Many-to-Many • There is no direct way to map many to many relationships • To represent an M:N relationship, a table is created (intersection table) for the relationship Orders Parts OrderItems

  19. Transforming N:M Example • Many-to-Many is designed as two One-to-Many relationships • Create an intersection table with the primary key from each original table as foreign keys • The intersection table usually has a composite primary key 1:N N:1

  20. M:N Relationship Exercise MovieId PerformerId Movies Performers Cast FirstName Title Character LastName Length Gender

  21. Summary • E-R diagram is used widely for database design • Remember the rules to transform ERD to actual tables and relationships • One to one • One to many • Many to many

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