> For the complete documentation index, see [llms.txt](https://comunity.gitbook.io/learning.comunityplatform/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://comunity.gitbook.io/learning.comunityplatform/26.x/reference-articles/table-links.md).

# Table Links

Entity-relationship (ER) models are based on real-world entities and their relationships. Developers understand these systems just by looking at the ER diagram. ER models are normally represented by ER diagrams.

![](/files/asMqbfWOktWMJwJK67Id)

### Components

An ER diagram basically has three components:

* **Entities** − It is a real-world thing that can be a person, place, or even a concept. For example, Department, Admin, Courses, Teachers, Students, Building, etc are some of the entities of a School Management System.
* **Attributes** − An entity that contains a real-world property called an attribute. For example, the entity employee has properties like employee id, salary, age, etc.
* **Relationship** − Relationship tells how two attributes are related. For example, an employee works for a department.

### Relationship Types

* A **One-to-Many relationship** in a DBMS is a relationship between instances of an entity with more than one instance of another entity.
* A **Many-to-One relationship** in a DBMS is a relationship between more than one instance of an entity with one instance of another entity.
* A **Many-to-Many relationship** in a DBMS is a relationship between more than one instance of an entity with more than one instance of another entity i.e. both the entities can have many relationships between each other.
* A **One-to-One Relationship** is an association with the same entity between the same instances represented by the same role group.

For more information, go to [https://docs.microsoft.com/en-us/ef/ef6/fundamentals/relationship](https://docs.microsoft.com/en-us/ef/ef6/fundamentals/relationships)