Enhanced entity–relationship model - Wikipedia
When designing your database, an entity-relationship diagram (ER or ERD) is an excellent way to visually lay out your plan. But in some cases. The Extended Entity-Relationship (EER) model is a conceptual. (or semantic) data model, capable of describing the data requirements for a new information. LECTURE 3. Enhanced Entity-. Relationship Models (EER). Dr. Philipp Leitner [email protected] @xLeitix.
Each attribute can have Values. In most cases single attribute have one value. But it is possible for attributes have multiple values also. For example Peter's age has a single value. But his "phone numbers" property can have multiple values.
Entities can have relationships with each other. Let's consider a simplest example. Assume that each Microsoft Programmer is given a Computer. It is clear that that Peter's Computer is also an entity.
Peter is using that computer and the same computer is used by Peter. In other words there is a mutual relationship among Peter and his computer. In Entity Relationship Modeling, we model entities, their attributes and relationships among entities. EER Models supports more details design. EER Modeling emerged as a solution for modeling highly complex databases.
UML is the acronym for Unified Modeling Language; it is a general purpose modeling language used when designing object oriented systems. Entities are represented as class diagrams. Relationships are represented as associations between entities. Why use ER Model? Now you may think why use ER modeling when we can simply create the database and all of its objects without ER modeling?
One of the challenges faced when designing database is the fact that designers, developers and end-users tend to view data and its usage differently. If this situation is left unchecked, we can end up producing a database system that does not meet the requirements of the users.
ER models are examples of such tools. ER diagrams also increase user productivity as they can be easily translated into relational tables. We will using this database for all hand-on in the remainder of this tutorials MyFlix is a business entity that rents out movies to its members.
Enhanced Entity Relationship Model (EER Model)
MyFlix has been storing its records manually. The management now wants to move to a DBMS Let's look at the steps to develop EER diagram for this database- Identify the entities and determine the relationships that exist among them. Each entity, attribute and relationship, should have appropriate names that can be easily understood by the non-technical people as well.
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.
It minimizes the difference between the entities by identifying the common features.
What is ER Modeling? Learn with Example
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.
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.
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. It is a process when two entity is treated as a single entity.