Enhanced Entity Relationship Model (EER Model)
EER Enhanced Entity Relationship Model PowerPoint PPT Presentation Aggregation relationship between object and component parts (has-a relationship). Entity Relationship (ER) Model – represents an object Enhanced Entity Relationship (EER) – Data Modeling; EER shows complex relationships between . EER stands for Enhanced ER or Extended ER; EER Model Concepts. Includes EER includes some object-oriented concepts, such as inheritance. Slide 4- 4.
An entity cannot exist in the database merely by being a member of a subclass; it must also be a member of the superclass. But, in general, it is not necessary that every entity in a superclass be a member of some subclass.EER MODEL
An entity in the subclass represents the same real-world entity from the superclass, it should posses values for its specific attributes as well as values of its attributes as a member of the superclass.
We say that an entity that is a member of a subclass inherits all the attributes of the entity as a member if superclass. The entity in the subclass also inherits all the relationships in which the superclass participates. Members of the specialization are defined based on some distinguishing characteristics of the entities in the superclass.
We may have several specializations of the same entity type based on different distinguishing characteristics.
Think about method of pay or type of job as characteristics. A subclass may have additional attributes, which are called specific attributes or local attributes of the subclass. Also, a subclass may participate in additional relationship type specific relationship types. Define a set of subclasses of an entity type, Establish additional specific attributes with each subclass, Establish additional specific relationship types between each subclass and other entity types or other subclasses.
Generalization it is the reverse process of abstraction in which we suppress the differences among several entity types, identify their common features, and generalize them into a single superclass of which the original entity types are special subclasses.
Chapter 4 The Enhanced Entity-Relationship (EER) Model - PowerPoint PPT Presentation
Generalization is the process of defining a generalized entity type from the given entity types. In some specialization we can do this by placing a condition on the value of some attribute of the superclass.
Such subclasses are called predictive-defined or condition-defined subclasses. If all subclasses in a specialization have a membership condition on the same attribute of the superclass, the specialization itself is called an attribute-defined specialization, and the attribute is called the defining attribute of the specialization. Membership in such a subclass is determined by the database users when they apply the operation to add an entity to the subclass.
Each membership is specified individually for each entity by the user, NOT by any condition that may be evaluated automatically. Two other constraints may apply to specialization: This means that an entity can be a member of at most one of the subclasses of the specialization.
It includes all modeling concepts of the ER model. Diagrammatic technique helps for displaying the EER schema. It includes the concept of specialization and generalization. It is used to represent a collection of objects that is union of objects of different of different entity types.
Chapter 41 Enhanced Entity-Relationship and Object Modeling. - ppt download
The relationship between sub class and super class is denoted with symbol. Super class is an entity type that has a relationship with one or more subtypes. An entity cannot exist in database merely by being member of any super class.
Shape super class is having sub groups as Square, Circle, Triangle. Sub Class Sub class is a group of entities with unique attributes. Sub class inherits properties and attributes from its super class. Square, Circle, Triangle are the sub class of Shape super class. Specialization and Generalization 1.
Generalization Generalization is the process of generalizing the entities which contain the properties of all the generalized entities. It is a bottom approach, in which two lower level entities combine to form a higher level entity. Generalization is the reverse process of Specialization. It defines a general entity type from a set of specialized entity type.