Normalisation & ER Diagrams help!

Normalisation isn't my forte but I found a useful guide on this.
https://www.sqa.org.uk/e-learning/MDBS01CD/page_26.htm

With regards to ER diagrams, what parts are you struggling with?

"An entity relationship diagram (ERD) is a graphical representation of entities and their relationships to each other, typically used for modeling the organization of data within databases or information systems."



In this example, we have 6 entities containing information regarding bus route management.

- The primary key (indicated by a key) uniquely identifies a record in a database. E.g. each driver has their own ID number, this makes them unique in a database.
- The foreign key (indicated by the green arrow) uniquely identifies a record of another table in the same table, think of it like a reference to another primary key. E.g. each schedule has its own route, which is identified by a route ID in the route table.
- varchar, integer, float, date refers to the datatype for each column, the number in the bracket defines the character length.
- N refers to columns that can contain a NULL value.


Relationships...There are several to take note of here.

- One-to-one relationship: Between bus and schedule. Both tables can have only one record on either side of the relationship. Each bus has its own schedule and each schedule is used by a single bus.

- One-to-many relationship: Between route and schedule. The primary key table contains only one record that relates to none, one, or many records in the related table. A single route may have 1 or more schedules and 1 or more schedules are run by a single route.

- Many-to-many relationship: Between route and stop. Each record in both tables can relate to any number of records (or no records) in the other table. A route may have 1 stop or many stops, at the same time these stops may be present in 1 route or multiple routes. Notice how a third entity is created in a many-to-many relationship, this is known as a linking table or an associative entity.