Course Content
Relational Database and Normalization
3. Normalization and Normal Forms
Relational Database and Normalization
Entity-Relationship Model
Databases come in various sizes, comprising different numbers of tables and relationships. This is why we use diagrams when designing databases – they offer a visual representation of the database's structure.
Let's get acquainted with the most commonly used diagram in database design: the entity-relationship model (often abbreviated as ER model). For instance:

In this example, we have two entities: School and Student. The School entity boasts attributes like id, name, and location, whereas the Student entity features attributes such as id, name, and surname. There exists a relationship between the Student and School entities, which we label as "study".
In tables of relational databases, this can be depicted using a foreign key:


The "study" relationship is captured using a foreign key (the school_id column in this case).
Such models are instrumental in crafting a coherent database structure.
Concepts
The ER model is underpinned by three essential concepts:
- Entities: These can be tangible or abstract objects, like schools and students.
Represented by a Rectangle. - Attributes: These are features or properties tied to entities. For instance, a school might have attributes like location or founding year, while a student might have age or group.
Represented by an Ellipse. - Relationships: These signify the interactions or connections between entities or attributes.
Represented by a Rhombus.
You can see the graphical representation of these elements in the image provided:

Modern Entity-Relationship Diagram Presentation
Given that attribute shapes can take up a significant amount of space on a diagram, there's an alternative representation:

In this format, you'll notice a single-column table. The header denotes the entity, while each row below corresponds to the attributes linked to that entity.
Everything was clear?