Entity Relationship Modelling
Data Modeling
Introduction
Entity Relationship Modeling (ERM) a technique used to analyze & model the data in organizations using an Entity Relationship (E-R) diagram.
Database Management System 1
Isaac M Morallo – MAITE LPU - Laguna
Definitions
Entity
an aggregation of a number of data elements each data element is an attribute of the entity
Background
Introduced by Peter Chen in ‘75 now widely used You’ll find them in:
Structured Systems Analysis and Design Methodology (SSADM) Information Engineering (IE) Multiview Yourdon/DeMarco.
Entity type a class of entities with the same attributes
Relationship an association between two or more entities that is of particular interest
Why use ER Diagrams ? provides a global quick reference to an organization’s data structures. can be used individually to design an Information System’s (IS) data structure can be used with Data Flow Diagrams to provide a more comprehensive IS logical design.
ERD Development Process
Identify the entities Determine the attributes for each entity Select the primary key for each entity Establish the relationships between the entities Draw an entity model Test the relationships and the keys
A Simple Example
Identify the entities
Any entity can be classified in one of the following categories: Regular : any physical object, event, or abstract concept that we can record facts about.
STUDENTs attend COURSEs that consist of many SUBJECTs. A single SUBJECT (i.e. English) can be studied in many different COURSEs. Each STUDENT may only attend one COURSE.
Weak : any entity that depends on another entity for its existence.
Determine the Attributes
Every Entity has attributes. Attributes are characteristics that allow us to classify/describe an entity e.g., entity STUDENT has the attributes: student number name date of birth course number
Key Attributes
Certain attributes identify particular facts within an entity, these are known as KEY
Introduction
Entity Relationship Modeling (ERM) a technique used to analyze & model the data in organizations using an Entity Relationship (E-R) diagram.
Database Management System 1
Isaac M Morallo – MAITE LPU - Laguna
Definitions
Entity
an aggregation of a number of data elements each data element is an attribute of the entity
Background
Introduced by Peter Chen in ‘75 now widely used You’ll find them in:
Structured Systems Analysis and Design Methodology (SSADM) Information Engineering (IE) Multiview Yourdon/DeMarco.
Entity type a class of entities with the same attributes
Relationship an association between two or more entities that is of particular interest
Why use ER Diagrams ? provides a global quick reference to an organization’s data structures. can be used individually to design an Information System’s (IS) data structure can be used with Data Flow Diagrams to provide a more comprehensive IS logical design.
ERD Development Process
Identify the entities Determine the attributes for each entity Select the primary key for each entity Establish the relationships between the entities Draw an entity model Test the relationships and the keys
A Simple Example
Identify the entities
Any entity can be classified in one of the following categories: Regular : any physical object, event, or abstract concept that we can record facts about.
STUDENTs attend COURSEs that consist of many SUBJECTs. A single SUBJECT (i.e. English) can be studied in many different COURSEs. Each STUDENT may only attend one COURSE.
Weak : any entity that depends on another entity for its existence.
Determine the Attributes
Every Entity has attributes. Attributes are characteristics that allow us to classify/describe an entity e.g., entity STUDENT has the attributes: student number name date of birth course number
Key Attributes
Certain attributes identify particular facts within an entity, these are known as KEY