Enhanced entity relationship diagram adalah dimaklumkan

Enhanced Entity Relationship Model (EER Model)

enhanced entity relationship diagram adalah dimaklumkan

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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.

Enhanced Entity Relationship Model (EER Model)

Generalization is the reverse process of Specialization. It defines a general entity type from a set of specialized entity type. It minimizes the difference between the entities by identifying the common features.

enhanced entity relationship diagram adalah dimaklumkan

In the above example, Tiger, Lion, Elephant can all be generalized as Animals. Specialization Specialization is a process that defines a group entities which is divided into sub groups based on their characteristic. It is a top down approach, in which one higher entity can be broken down into two lower level entity.

enhanced entity relationship diagram adalah dimaklumkan

It maximizes the difference between the members of an entity by identifying the unique characteristic or attributes of each member. For example In the above example, Employee can be specialized as Developer or Tester, based on what role they play in an Organization. Category or Union Category represents a single super class or sub class relationship with more than one super class.

It can be a total or partial participation. For example Car booking, Car owner can be a person, a bank holds a possession on a Car or a company. A Category member must exist in at least one of its super classes.

enhanced entity relationship diagram adalah dimaklumkan

Aggregation Aggregation is a process that represent a relationship between a whole object and its component parts. It abstracts a relationship between objects and viewing the relationship as an object. The U-symbol indicates the Subtype is a subset of the Supertype.

All of attributes of the Supertype are also common to the Subtype. Each Subtype entity has attributes that are unique to that Subtype - that is what makes the entity a subtype.

Enhanced Entity-Relationship Model

All entities share a common identifier attribute. Subtypes inherit all of the attributes of the Supertype. Note that an occurrence of a Subtype entity represents an occurrence of the same Supertype entity. The primary key of the supertype and subtype are always identical. Minimum cardinality between the supertype and subtype are always 1: When to Use a Subtype.

Use this approach if an occurrence of a Subtype participates in a relationship. The Total Specialization Rule specifies that this is the case.

This is diagrammed with a double line from the Supertype to the circle as shown here. The Partial Specialization Rule is the one we have followed thus far in the notes single line to the circle -- no such constraint exists. This type of business rule deals with the situation where an occurrence of a Supertype may also have more than one Subtype occurrence.

The Disjoint Rule says that this cannot occur.