Attribute
Attribute: An attribute is a characteristic of an entity. Entities are represented using their
attributes. All attributes have their own specific values.
For example, an employee entity may have. Employee ID, emp_name, and salary as attributes.
In a database management system, an attribute is a database component, such as a field or column of a
table.
Example:
The entity student has attributes like student_id and student_name. In this, every attribute has a value. Here
101 is the value for the attribute student_id, and Kunal is the value for the attribute student_name.
10
Name
Student
ID
Contact no
There are five different types of attributes in a Database Management System :
1. Single-valued Attribute:
-A single-valued attribute is the attribute that can hold a single value for a single entity.
-Example: In the entity Student, student_name is the single-valued attribute since a student has a single value for the name attribute.
2. Multi-valued Attribute:
-A multi-valued attribute is an attribute that can hold multiple values for a single entity.
-Example: In the entity student, the attribute student_contact no could be considered a multi-value attribute since a student could have multiple contact numbers.
3. Simple Attributes :
-An attribute whose value cannot be further divided is known as a simple attribute. That means it is atomic in nature.
-Example In the entity student, the attribute student_age cannot be divided. Therefore student_age is the simple attribute of the student entity.
4. Composite Attribute:
-The composite attributes are the attri Utes which can be further divided into sub Parts. These subparts represent the basic entities with their independent meaning.
-Example In the entity student, student_name is the composite attribute, we can divide this attribute into Q free into different sub-parts: First_name, ddle_name •, and Last_name.
5. Derived Attribute:
-The attribute which does not physically exist in the database, but its value can be calculated from the other present attributes is known as a derived attribute.
-Example: In the entity student, we can calculate the average age of students. This average age is not physically present in the database but it can be derived from the attribute student_age;
- Relationships
The association between two different entities is called a relationship. In the real-world application, what does one entity do with the other, and how do they connect to each other
For example, An employee works at a department, or a student.no enrolls in a course. Here, works at and Enrolls are called relationships.
The Degree of Relationships
The degree of relationship refers to several entities that participated in the relationship.
1. Unary Relationship
- A unary relationship exists when there is a relation between a single entity. A unary relationship is also known as a recursive relationship in which an entity relates to itself.
- Example: A person can be in a relationship with another person, such as:-
- A woman who can be someone's mother
- A person that is someone's child.
2. Binary Relationship
- A binary relationship exists only when there is a relationship between only two entities. In this case, the regret: of radiation is two.
- Example: A teacher teaches students. In this teacher and student are two different entities which are connected with each other via. - relation Teaches.
3. Ternary Relationship
- A ternary relationship exists when there are relations between three entities. In ternary relation, the degree of relation is six.
- Example: A person can be a student and a person also can be a Her teacher. Here teac, her, student, and person are three entities that are related to each other.
4. Quaternary Relationship
- A quaternary relationship exists when there are relations between four entities. In quaternary relation, the degree of relation is eight.
- Example: The· four entities ·Employee, Management Faculty, Teaching Faculty, and Non-Teaching Faculty are connected with each other via a relationship.
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