Contents
What is a generalization specialization hierarchy?
A generalization hierarchy (also called is-a hierarchy) connects a superclass and one or more subclasses, representing a specialization of the superclass. Each subclass inherits the features (attributes, operations, and associations) defined in the superclass and may add locally defined features.
What is generalization hierarchy?
A generalization hierarchy is a structured grouping of entities that share common attributes. It is a powerful and widely used method for representing common characteristics among entities while preserving their differences. It is the relationship between an entity and one or more refined versions.
What is EER Modelling in DBMS?
The enhanced entity–relationship (EER) model (or extended entity–relationship model) in computer science is a high-level or conceptual data model incorporating extensions to the original entity–relationship (ER) model, used in the design of databases.
Which are the additional concepts added to ER model?
In addition to the same concepts that ordinary ER diagrams encompass, EERDs include: Subtypes and supertypes (sometimes known as subclasses and superclasses) Specialization and generalization. Category or union type.
What is the main concept of EER?
The Extended Entity-Relationship (EER) model is a conceptual (or semantic) data model, capable of describing the data requirements for a new information system in a direct and easy to understand graphical notation.
What is D EER diagram?
d means “disjoint”- what it tells is the subclasses must have disjoint sets of entities. 2.o means “overlap”The subclasses may have overlapping sets of entities. U symbol indicates the Subtype is a subset of the Supertype.
How do you create an enhanced entity relationship diagram?
Below points show how to go about creating an ER diagram.
- Identify all the entities in the system. An entity should appear only once in a particular diagram.
- Identify relationships between entities. Connect them using a line and add a diamond in the middle describing the relationship.
- Add attributes for entities.
Who are the authors of the enhanced entity relationship?
Chapter 8 The Enhanced Entity- Relationship (EER) Model Copyright © 2011 Ramez Elmasri and Shamkant Navathe Chapter 8 Outline Subclasses, Superclasses, and Inheritance Specialization and Generalization Constraints and Characteristics of Specialization and Generalization Hierarchies Modeling of UNION Types Using Categories
What is an enhanced entity relationship diagram ( Eerd )?
Enhanced entity-relationship diagrams, or EERDs, are specialized ER Diagrams that can be extremely useful for modeling your database. EERDs use several concepts that are closely related to object-oriented design and programming.
Which is an example of a relationship between an entity?
Some entities have relationships that form a hierarchy. For example, a shipping company can have different types of ships for its business. The relationship that exists between the concept of the ship and the specific types of ships forms a hierarchy. The ship is called a superclass.
Which is an example of a generalization relationship?
Generalization: Multiple entity sets are synthesized into a higher-level entity set, based on common features (bottom-up). A diamond notation is a common representation of specialization/generalization relationships in ER diagrams. Figure 7.10 As an example, let’s consider the following scenario: