2- Entities, Attributes and Relations

In this article we are going to study Database Conceptual Model in more depth.

The Basic Components of Database Conceptual Model are.

  • Entities

  • Attributes

  • Relations

In the recent article we learned what is the Database, Database Conceptual Model and the benefits of using conceptual model .

At the end of this article you will be able to know.

  • The importance of using the Conceptual Model.

  • What is the Entity with examples ?

  • What is the Attributes with examples ?

  • The Relation with examples.

Entity Relation Model.

Is a paradigm used to describe the understanding of the information requirements of a business, This paradigm used to draw  diagrams which are easy to understand and can be edited easily.

Merits and Benefits of Using Entity Relation Model.

  • Organize all the required data of a business.

  • A set of consistent database tables are the result of using Entity Relation Model.

Entity Relation Model Rules And Requirements.

  • The Conceptual Model must be complete.
  • All business requirements must be known and available before beginning.
  • Every piece of information appears only once in the model.
    This is an important point, suppose that you are a user of an information system and found that the system displays a different values of the same data, which value would be trust.
  • System must not include any piece of information that can be derived from already modeled data.
  • System must ensure that data are located at a logical and predictable place.

Entity .

Is something related to business and it's important to have data about, something you can put in a list.
Entity contains instances. In the table below, you will find some examples of entities and instances.

Difference between Entity and Instance
 
Entity  Instance
Employee Mohammad Ahmad
Job Engineer
Skill Level Very Good

We can say that the Entity is a set of instances .

Entity represents a set Instances
Example of an Entity and its Instances

 

As you will see in details later, At the end of modeling process  an entity will be transformed to a database table and instances will be the rows of that table.

Attributes.

Attribute is a small peace of information related to the entity, attributes are used to describe, classify, quantify or specify  the entity. Entities contain many attributes.

While an entity contains instances, an attribute contains values.

The following table displays some Entities and their attributes.

 Entity  Attribute
Job Title, Description, Responsibility, ...
Employee Name, Last Name, Address, Phone, Age.....
Product Name, Description, Weight, Color

Unstable Attributes.
Some attributes are unstable like age, age depends on the time it will be calculated at, Instead of using age as attribute it's better to use birth date which will not change.

Relations.

Relation connects two entities or one entity to itself.

Examples of relations.

Employee performs Job
Job held by Employee

Product categorized by Product Type
Product Type categorize Product

Order has Items
Item is related to Order

In this article you have learned about Database Conceptual Model and its main components Entities, Attributes and Relations.

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