Computer Science ADBMS EBOOK - ADBMS Notes- PDF Download
Computer Science ADBMS EBOOK
Preview of the attached ebook
In computer science, the enhanced entity-relationship (EER) model is a high-level or conceptual data model incorporating extensions to the original entity-relationship (ER) model, used in the design of databases. It was developed to reflect more precisely the properties and constraints that are found in more complex databases, such as in engineering design and manufacturing (CAD/CAM), telecommunications, complex software systems and geographic information systems (GIS).
Subclass and superclass
Entity type Y is a subtype (subclass) of an entity type X if and only if every Y is necessarily an X. A subclass entity inherits all attributes and relationships of its superclass entity. A subclass entity may have its own specific attributes and relationships (together with all the attributes and relationships it inherits from the superclass. One of the most common superclass examples is a vehicle with subclasses of Car and Truck. There are a number of common attributes between a car and a truck, which would be part of the Superclass, while the attributes specific to a car or a truck (such as max payload, truck type...) would make up two subclasses.
Please download the attached file along to view rest of the content