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An entity relationship diagram (ERD), also known as an entity relationship model, is a graphical representation that depicts relationships among people, objects, places, concepts or events within an information technology (IT) system.
ERD in SQL
is a visual representation of the table’s structure and the relationships between logically related tables. In ER modeling the database structure is represented as a diagram known as ER diagram (ERD). An ER diagram gives a better understanding of the overall database structure.How does an ERD work?
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An ERD visualizes the relationships between entities like people, things, or concepts in a database. An ERD will also often visualize the attributes of these entities. By defining the entities, their attributes, and showing the relationships between them, an ER diagram can illustrate the logical structure of databases.What are the 4 ERD rules?
1.Provide a precise and appropriate name for each entity, attribute, and relationship in the diagram. …
2.Remove vague, redundant or unnecessary relationships between entities.
3.Never connect a relationship to another relationship.
4.Make effective use of colors.How do you ERD a database?
1.Write a sentence or two about what you are storing data about.
2.List what you’re storing data about – the nouns/objects.
3.List the information you want to store for each object.
4.Describe the relationships between each object.
5.Draw the diagram.Class diagrams are the blueprints of your system or subsystem. You can use class diagrams to model the objects that make up the system, to display the relationships between the objects, and to describe what those objects do and the services that they provide. Class diagrams are useful in many stages of system design.
They are used to show the different objects in a system, their attributes, their operations, and the relationships among them. The following figure is an example of a simple class: Simple class diagram with attributes and operations.
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