Data Base Management System Lecture 2
Main note
Looking back
Weak entity Strong entity Whenever there is a strong entity in the DB we create an entity.
Converting Strong Entity TYpes
- Each Entity type becomes a table.
- We Underline the primary key.
- each single valued attribute becomes a column
- Derived Attributes are ignored
- Composite attributes are represented by components.
- Multi Valued attributes are represented by a separate table.
- The key attribute of the entity becomes the primary key of the table.
Here we have multiple variables.Data Base Table1.excalidraw
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Excalidraw Data
Text Elements
Employee
Address
Street
Street
Street
Name
Date of joining
Years of service
Skillset
Derived Attribute
Link to original
- other entities with multiple attributes have their own table.
Converting Weak Entity
Definition
The weak entities only exist if the strong entity related to it exists.
Relevance
If the strong entity is deleted then the weak entity related to it will get destroyed as well.
Dependancy.excalidraw
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Excalidraw Data
Text Elements
Employee
Has
Dependant
ID
Name
Address
Emp ID
Skillset
Link to original
Converting Relationships
Binary 1:1
Conversion 1isto1.excalidraw
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Excalidraw Data
Text Elements
Employee
Department
Manages
Partial
Total
Link to original
Binary 1:N
1istoN.excalidraw
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Excalidraw Data
Text Elements
Teacher
Subject
Teaches
1
n
Link to original
Binary M:N
Self Refencing 1:1
Self Referencing M:N
References
Information
- date:: 2024.07.24
- time:: 15:0615:0615:06