Its job is to allocate limited resources and distribute output among a large number of agents-mainly individuals, firms, and governments-allowing for the possibility that each agent’s action can directly (or indirectly) affect other agents’ actions.Īdam Smith labeled the machine the “invisible hand.” In The Wealth of Nations, published in 1776, Smith, widely considered the father of economics, emphasized the economy’s self-regulating nature-that agents independently seeking their own gain may produce the best overall result for society as well. When more than one instance of the entity on the left, and more than one instance of an entity on the right associates with the relationship then it is known as a many-to-many relationship.įor example, Employee can assign by many projects and project can have many employees.Finance & Development, June 2011, Vol. When more than one instance of the entity on the left, and only one instance of an entity on the right associates with the relationship then it is known as a many-to-one relationship.įor example, Student enrolls for only one course, but a course can have many students. ![]() ![]() When only one instance of the entity on the left, and more than one instance of an entity on the right associates with the relationship then this is known as a one-to-many relationship.įor example, Scientist can invent many inventions, but the invention is done by the only specific scientist. When only one instance of an entity is associated with the relationship, then it is known as one to one relationship.įor example, A female can marry to one male, and a male can marry to one female. Diamond or rhombus is used to represent the relationship. It can be represented by a dashed ellipse.įor example, A person's age changes over time and can be derived from another attribute like Date of birth.Ī relationship is used to describe the relation between entities. The double oval is used to represent multivalued attribute.įor example, a student can have more than one phone number.Īn attribute that can be derived from other attribute is known as a derived attribute. These attributes are known as a multivalued attribute. The composite attribute is represented by an ellipse, and those ellipses are connected with an ellipse.Īn attribute can have more than one value. The key attribute is represented by an ellipse with the text underlined.Īn attribute that composed of many other attributes is known as a composite attribute. The key attribute is used to represent the main characteristics of an entity. Eclipse is used to represent an attribute.įor example, id, age, contact number, name, etc. The attribute is used to describe the property of an entity. The weak entity is represented by a double rectangle. The weak entity doesn't contain any key attribute of its own. can be taken as an entity.Īn entity that depends on another entity called a weak entity. In the ER diagram, an entity can be represented as rectangles.Ĭonsider an organization as an example- manager, product, employee, department etc. The address can be another entity with attributes like city, street name, pin code, etc and there will be a relationship between them.Īn entity may be any object, class, person or place. In this database, the student will be an entity with attributes like address, name, id, age, etc.
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