Entity-Relationship Data Model: Introduction to Database Design, Summaries of Aquaculture and Aquafarming

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Chapter 2Entity-RelationshipData Model

Introduction2DB - FIT - HCMUS^

Content
^ Process of database design
^ E/R model
^ E/R model design
^ Exercise

Introduction2DB - FIT - HCMUS^

DBMS-independent^ DBMS-specific^4

Process of database design^ Miniworld^ Requirements analysis^ Data requirements^ Conceptual design^ Conceptual schema^ Logical design^ Logical schema^ Physical designInternal schema

Functional requirements Functional analysisHigh-level function specification Application programdesign^ Application^ Applicationprogramsimplementation

Introduction2DB - FIT - HCMUS^

Content
^ Process of database design
^ E/R model^ -^ Entity^ -^ Attribute^ -^ Relationship^ -^ E/R schema^ -^ Keys in E/R model^ -^ Weak entity
^ E/R model design
^ Example

Introduction2DB - FIT - HCMUS^

Entity sets
^ An entity is an abstract object in the real world^ -^ Physical existence (person, car, house…)^ -^ Conceptual existence (company, job, university course...)
^ A collection of similar entities forms an entity set
^ Note^ -^ Entity^ -^ Object^ -^ Entity set^ -^ Class of objects

Structure of data Operations on data

Introduction2DB - FIT - HCMUS^

Entity sets
^ Example^ “Company” database^ -^ An employee is an entity^ -^ The set of all employees constitutes an entity set^ -^ Projects are entities^ -^ The set of projects is an entity set^ -^ A department is another kind of entity^ -^ The set of departments is an entity set

Introduction2DB - FIT - HCMUS^

Relationships
^ The connections among two or more entity sets
^ Example^ -^ Relationships between entity sets EMPLOYEE andDEPARTMENT^ •^ Each employee works for a department^ •^ Each^ department^ has

an^ employee^ who^ manages

that department

Introduction2DB - FIT - HCMUS^

E/R diagrams
^ A^ graph^ representing

entity^ sets,^ attributes,

and

relationships -^ Nodes^ NAME^ Entity sets^ NAME^ Attributes^ Name^ Relationships -^ Edges connect^ •^ An entity set and its attributes^ •^ A relationship and its entity sets

Introduction2DB - FIT - HCMUS^

Instances of an E/R diagram
^ A^ DB^ described^ by^

an^ E/R^ diagram^ will^ containparticular data, which is called the DB instance - Each entity set, the instance will have a particular finiteset of entities • Entity set EMPLOYEE has entities such as E, E, …, E^12

n

-^ Each of entity has particular values for each attribute^ •^ Ehas FName=^ “ Tung^ ”, BirthDate=^1

“ 08/12/1955^ ”, Sex=^ “ Nam^ ”

-^ Ehas Fname=^ “ Hang^ ”, BirthDate=^2

“ 07/19/1966^ ”, Sex=^ “ Nu^ ”

^ Note^ -^ Do not store E/R data directly in a DB^ •^ Is abstract only^ •^ Help us to think about the design before we convert to relations

Introduction2DB - FIT - HCMUS^

Relationship – Instance
^ DB^ instance^ includes

specific^ choices^ of

the

relationships of the diagram -^ A relationship R connects n entity sets E

, E, …, E 12 n

-^ Instance of R consists of a finite set of lists (e

, e, …, e) 12 n

-^ Each eis chosen from the entities that are in Ei^

i

^ Example^ EMPLOYEE^

Works_forEMPLOYEE DEPARTMENTDEPARTMENT TungNghien cuu(Tung, Nghien cuu)(Hang, Dieu hanh)HangDieu hanh(Vinh, Quan ly)Vinh Quan ly

Introduction2DB - FIT - HCMUS^

Relationship – Multiplicity
^ Many-One from E to F ~ One-Many from F to E^ •^ Each^ member^ of^ E^

can^ be^ connected^ at^ most

one member of F • Each member in F can be connected to many members ofE^ E^

(1, n)(1,1)R F r (^1)  e
1
f^1 r (^2)  e
2
f^2 r (^3) e
^ … 3  r (^4) e
4  … …

Introduction2DB - FIT - HCMUS^

Relationship – Multiplicity
^ One-One from E to F^ -^ A member of either entity set can be connected to atmost one entity of the other set^ E^

(0,1)^ (1,1)RF r^1  e
1
f^1 r^2  e
2
f^2 r^3 e
3 ^
f^3 … e
4 … …

Introduction2DB - FIT - HCMUS^

Relationship – Multiplicity
^ (min,max)^ specifies^

the^ minimum^ or^ maximumnumber that each entity e^ ∈^ E can participate in R (min, max) (min, max)R E F • (0,1) – zero or 1 • (1,1) – at least 1 and at most 1 • (0,n) – zero or many • (1,n) – 1 or many

Introduction2DB - FIT - HCMUS^

Relationship – Multiplicity
^ Example^ -^ A department has many employees^ EMPLOYEE^ -^ An employee works for a department^ -^ An employee can work on many projects or do not workon any projects^ -^ An employee can manage a certain department

(1,n)DEPARTMENTWorks_for (1,1) EMPLOYEE DEPARTMENTWorks_for (0,n) EMPLOYEE PROJECTWorks_on (0,1) EMPLOYEE DEPARTMENTManages