24. What is an ERD. Define the RED related terms, including entities, attributes, cardinalities and relationships

ERD

An Entity Relationship Diagram (ERD) is a visual tool used to represent the relationships between different entities within a database or application. It is created during the design phase to structure the database, but can also be used to analyze and improve existing systems. ERDs use symbols to represent entities and their relationships, providing a clear and concise depiction of complex systems. ERDs can help identify issues and optimize database structure, making it an essential skill for database design (Brumm, 2019).

Entity, Relationship and Attributes make up an Entity Relation Diagram.

(Geissinger, 2017)

Entity

Entities are fundamental components in data storage. They are commonly illustrated as rectangles on an Entity Relationship Diagram (ERD). Entities can be classified as either strong or weak. Strong entities possess their own unique identifier, also known as a primary key, and do not rely on other entities. Conversely, weak entities depend on a strong entity and have a foreign key associated with it (Brumm, 2019). 

Relationship

In database design, relationships between entities are crucial to understanding how data is organised and connected. These relationships are represented in an Entity Relationship Diagram (ERD) and are derived from verbs that describe the interactions between entities. Relationships are visually depicted as lines connecting entities, with labels that provide further information about the nature of the relationship. There are three main types of relationships: one-to-one, one-to-many, and many-to-many (Brumm, 2019). 

Attributes

Attributes are essential properties of an entity that describe it and can be represented as an oval or an entry inside an entity. These attributes come in different types, including simple, composite, and derived. Simple attributes cannot be divided into other attributes, while composite attributes can be split into other attributes. Derived attributes, on the other hand, are calculated from other attributes (Brumm, 2019).

Moreover, attributes can be single-value, which is captured once for an entity, or multi-value, which can be captured more than once. For instance, an entity can have multiple phone numbers, making it a multi-value attribute (Brumm, 2019).

References

Brumm, B. (2019). A Guide to the Entity Relationship Diagram (ERD). [online] Database Star. Available at: https://www.databasestar.com/entity-relationship-diagram [Accessed 15 Mar. 2023].

Geissinger, M. (2017). Black Server Racks on a Room. [Online Image] Pexels. Available at: https://www.pexels.com/photo/black-server-racks-on-a-room-325229/ [Accessed 15 Mar. 2023].

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