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Logical Data Modelling Concepts
Transcript of Logical Data Modelling Concepts
Entities & Attributes
A database contains one or more related tables
Each table holds all of the information about an object, person or thing
Examples include - Customer table, Video table, Appointment table
Customer, Video and Appointment are all types of Entities
An entity is a person, place, thing or concept about which data can be collected
one-to-one - think about a husband and wife relationship
A husband can only have one wife
A wife can only have one husband
one-to-many - think about mother and her children
A mother can have many children
A child can only have one mother
many-to-many - think about video games and customers
Video games can be bought by many customers
Customers can buy many video games
Entity Relationship Diagrams
What do I need to do for P3 of the assignment?
Produce a detailed presentation (with notes) to explain the logical data modelling concepts.
By the of the lesson
Re-view understanding of...
entities, attributes, relationships
entity relationship diagrams
participation conditions of relationships
What needs to be covered for P3
Participation Condition of Relationships
Mandatory and Optional
In a relationship between entities you can indicate whether the relationship between entities is mandatory or optional. You define options from the point of view of both entities in the relationship..
An entity is made up of a number of 'Attributes" which represent that entity
For Example, a Customer entity would have attributes Customer ID, First Name, Surname, Date of Birth, Address, Phone no.
A data dictionary is a central store of information about all of the data in a database.
It is used to represent table and fields that are going to be used to build a relational database (showing the data types and validation to be used)
In this example relationship a mother can exist without a child, but a child or children always have to have a mother
Mandatory & Optional
So a mother (mandatory end of relationship) has to exist in order to have a child or children (optional end of relationship)
These relationships can be shown in the form of a diagram - known as an Entity Relationships Diagram (ERD)
They are diagrams that represent the relationships between tables in a database
They are made up of two components
entity (to represent the database tables)
relationship (which represents the link between the two tables)
They show how all of the data items stored in a relational database relate to each other