Understanding Entity and Relationship Diagram
Defining Entity and Relationship Diagram
According to Biscobing (2019), an entity relationship diagram (ERD), referred to as an entity-relationship model, is a visual illustration illustrating connections between individuals, items, locations, ideas, or occurrences within an information technology (IT) system. ERDs employ data modelling methods that can clarify business procedures and establish the groundwork for a relational database.
Biscobing (2019) also determines how to create and ERD in 3 steps:
-A conceptual data model, which lacks specific detail but provides an overview of the scope of the project and how data sets relate to one another.
-A logical data model, which is more detailed than a conceptual data model, illustrating specific attributes and relationships among data points. While a conceptual data model does not need to be designed before a logical data model, a physical data model is based on a logical data model.
-A physical data model, which provides the blueprint for a physical manifestation -- such as a relational database -- of the logical data model. One or more physical data models can be developed based on a logical data model.
Five Basic Components of an ERD
An entity relationship diagram consists of five fundamental elements, with similar elements represented using consistent shapes. For instance, all entity types may be enclosed within rectangles, while attributes are depicted within diamonds. These components encompass:
Entities, representing objects or concepts eligible for data storage. In the context of databases, entities correspond to tables.
Attributes, signifying properties or characteristics of entities. An ERD attribute can take on the role of a primary key, which uniquely identifies an attribute, or a foreign key, which can be linked to multiple attributes.
The relationships existing among these entities.
Actions, which describe the methods through which entities exchange information within the database.
Connecting lines, facilitating the visualization of connections and associations.
Cardinalities
"Cardinalities can denote that an entity is optional (for example, a sales rep could have no customers or could have many) or mandatory (for example, there must be at least one product listed in an order" (Biscobing, 2019).
The three main cardinalities are:
A one-to-one relationship (1:1). For example, if each customer in a database is associated with one mailing address.
A one-to-many relationship (1:M). For example, a single customer might place an order for multiple products. The customer is associated with multiple entities, but all those entities have a single connection back to the same customer.
A many-to-many relationship (M:N). For example, at a company where all call center agents work with multiple customers, each agent is associated with multiple customers, and multiple customers might also be associated with multiple agents.
Reference(s):
Grubnyak, A (2018) Low-angle photography of metal structure Available at: Low-angle photography of metal structure photo – Free Grey Image on Unsplash (Accessed: 06/09/2023)
Biscobing, J (2019) TechTarget Available at: What is Entity Relationship Diagram (ERD)? | Definition from TechTarget (Accessed: 06/09/2023)
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