What ia an ERD. Define the ERD related terms, including entities, attributes, cardinalities and relationships

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 What is ERD

Entity relationship diagram also refer as ERD, ER model or diagram is a type of diagram based on database desing, ERD contains different symbols and connectors that visualize two important information; the major entities within the system scope and the inter-relationship among these entities.

But what is an entity?

we often refer to this as people for example students which is a tangible object, and tangible business objects eg product, relationship is about how these entities relate each other within the system.

source:https://www.freepik.com/free-vector/cloud-services-isometric-composition-with-characters-working-people-cabinet-with-folders-server-capsule-vector-illustration_23128898.


An ER diagram have entities, attributes and relationshops and we will explain each of these symbols;

Entity Atributtes 

has a name that describe the type and king of an attribute such as varchar for a string and int for integer, when a ERD is draw it is important to ensure the use of types that are supported by the target RDMS.

Primary Key 

Is a special kind of attribute that uniquely defines a record in a database table, in other words there can not be more than one or two that share the same value.

Foreing Key 

Referenced to a primary key in a table used to identify the relationship between entities, this means that foreing keys does not need to be unique, multiple records can share the value. 

Different Cardinalities

  • One to one 
  • one to many 
  • many to many 

reference:

(No date) What is entity relationship diagram (ERD)? Available at: https://www.visual-paradigm.com/guide/data-modeling/what-is-entity-relationship-diagram/ (Accessed: 06 September 2023).

Free vector: Cloud services isometric composition with characters of working people and Cabinet with folders and server capsule vector illustration (2022) Freepik. Available at: https://www.freepik.com/free-vector/cloud-services-isometric-composition-with-characters-working-people-cabinet-with-folders-server-capsule-vector-illustration_23128898.htm#query=database&position=0&from_view=search&track=sph (Accessed: 06 September 2023).


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