Database Models: Entity Relationship Modeling 
Database Models s L11: ER Diagrams
Kieran Herley
Summary The database design process and the role of ER modelling in same. Basic constituents of ER diagrams: entities, relationships and attributes.
While designing database it’s handy to have notation to “sketch” schema s Two common diagrammatic notations: x x s UML diagrams (Universal Modelling Language) ER diagrams (Entity Relationship) → cs1106 choice
Captures the information requirements of our database: what data it con and how these interrelate
[TOC]
ER Di
Database Development Process
1. Requirements analysis: figure out what is required of our database 2. Design: s s s s
Entities
Develop an ER diagram to sketch a design that meets these requirements “Translate” ER diagram into detailed DB schema
An entity is a “thing” e.g. a person An entity set is a collection of similar entities e.g. a collection of persons s An attribute is some property of the entities in an entity set e.g. the dat birth of each person
3. Implementation: Generate SQL code for design
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ER Diagrams – 3 / 18
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ER Di
Entities in ER Diagrams s Relationships
Relationship captures a connection between two or more entity sets s Example: s Will represent entity sets using rectangles, attributes as ovals
x x
Entity sets: students, modules Relationships: s s
is taking: Alice is taking cs1106 loves: Bob loves cs1109
s
Entity set eaters has attributes name and address; each entity with this set has a value for each attribute
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ER Diagrams – 5 / 18
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ER Di
Relationships in ER Diagrams s A More Complex Example
Key:
s s s
We use diamonds to depict relationships
Restaurants serve some foods Eaters like some foods Eaters frequent some restaur
s
Connect diamond to entity sets involved in relationship
[TOC]
ER Diagrams – 7 / 18
[TOC]
ER Di
Relationship Sets
The “value” of an entity set is the set of entities that
Kieran Herley
Summary The database design process and the role of ER modelling in same. Basic constituents of ER diagrams: entities, relationships and attributes.
While designing database it’s handy to have notation to “sketch” schema s Two common diagrammatic notations: x x s UML diagrams (Universal Modelling Language) ER diagrams (Entity Relationship) → cs1106 choice
Captures the information requirements of our database: what data it con and how these interrelate
[TOC]
ER Di
Database Development Process
1. Requirements analysis: figure out what is required of our database 2. Design: s s s s
Entities
Develop an ER diagram to sketch a design that meets these requirements “Translate” ER diagram into detailed DB schema
An entity is a “thing” e.g. a person An entity set is a collection of similar entities e.g. a collection of persons s An attribute is some property of the entities in an entity set e.g. the dat birth of each person
3. Implementation: Generate SQL code for design
[TOC]
ER Diagrams – 3 / 18
[TOC]
ER Di
Entities in ER Diagrams s Relationships
Relationship captures a connection between two or more entity sets s Example: s Will represent entity sets using rectangles, attributes as ovals
x x
Entity sets: students, modules Relationships: s s
is taking: Alice is taking cs1106 loves: Bob loves cs1109
s
Entity set eaters has attributes name and address; each entity with this set has a value for each attribute
[TOC]
ER Diagrams – 5 / 18
[TOC]
ER Di
Relationships in ER Diagrams s A More Complex Example
Key:
s s s
We use diamonds to depict relationships
Restaurants serve some foods Eaters like some foods Eaters frequent some restaur
s
Connect diamond to entity sets involved in relationship
[TOC]
ER Diagrams – 7 / 18
[TOC]
ER Di
Relationship Sets
The “value” of an entity set is the set of entities that