Скачать или смотреть What is an Entity-relationship model? Entities | Relationships | Generalization | Specialization

Welcome back MechanicaLEi, did you know that an ER or Entity-Relationship model defines a data or information structure which can be implemented in a database? This makes us wonder, What is an Entity-relationship model?
Before we jump in check out the previous part of this series to learn about what Database Modelling is? Now, An Entity-Relationship Model, or simply put, an ER model is a graphical approach to database design. It uses Entities and their Relationships to represent real-world objects. An Entity is a thing or object in the real world that is distinguishable from the surrounding environment. For example, each employee of an organization is a separate entity. Entities are represented by means of their properties, called attributes. All attributes have values. For example, a student entity may have name, class, and age as attributes. The association among entities is called a relationship. For example, an employee works_at a department, Here, Works_at is called a relationship between employee and department. The ER Model has the power of expressing database entities in a conceptual hierarchical manner. As the hierarchy goes up, it generalizes the view of entities, and as we go deep in the hierarchy, it gives us the detail of every entity included. Going up in this structure is called generalization, where entities are clubbed together to represent a more generalized view. For example, a particular student named Mira can be generalized along with all the students. The entity shall be a student, and further, the student is a person. The reverse is called specialization where a person is a student, and that student is Mira. Hence, we first saw what Entity relationship model is and then went on to see what generalization and Specialization are?
In the next episode of MechanicaLEi find out what an Extended Entity-Relationship model is?

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