What is weak entity and strong entity?
What is weak entity and strong entity?
Weak entity is dependent on strong entity and cannot exists without a corresponding strong. It has a foreign key which relates it to a strong entity. A weak entity is represented by double rectangle. Relationship between a strong entity and a weak entity is represented by double diamond.
What is strong entity and weak entity with example?
A weak entity is one that can only exist when owned by another one. For example: a ROOM can only exist in a BUILDING. On the other hand, a TIRE might be considered as a strong entity because it also can exist without being attached to a CAR.
What are strong entities?
A strong entity is complete by itself and is not dependent on any other entity type. It possess a primary key which describes each instance in the strong entity set uniquely. That means any element in the strong entity set can be uniquely identified.
What is a weak entity type?
In a relational database, a weak entity is an entity that cannot be uniquely identified by its attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key.
What is the main difference between strong and weak entity set?
Difference between Strong and Weak Entity
| S.No. | Strong Entity | Weak Entity |
|---|---|---|
| 3 | It is depicted by a sole rectangle. | It is depicted by a dual rectangle. |
| 4 | The connection between two strong entities is shown by a sole diamond. | The connection between a weak and a strong entity is shown by a dual diamond. |
How do you identify a weak entity?
Weak entity is represented by double rectangle. The relation between one strong and one weak entity is represented by double diamond. Weak entities are represented with double rectangular box in the ER Diagram and the identifying relationships are represented with double diamond.
Is student a strong entity?
Two strong entity sets “Student” and “Course” are related to each other. Student ID and Student name are the attributes of entity set “Student”. Student ID is the primary key using which any student can be identified uniquely. Course ID and Course name are the attributes of entity set “Course”.
Is employee a weak entity?
The EMPLOYEE entity has attributes as Emp_id, Emp_name, Job_title, Age, Salary, Address. And, the DEPENDANT has attributes as Name, Age and Relation. So, Emp_id is the key attribute of the EMPLOYEES entity type. So, EMPLOYEES is a strong entity and DEPENDANT is a weak entity.
How do I find a strong entity?
A strong entity will always have a primary key. Strong entities are represented by a single rectangle. The relationship of two strong entities is represented by a single diamond….Difference between Strong and Weak Entity:
- Strong entity always has a primary key.
- Strong entity is not dependent on any other entity.
What is a strong entity set?
Strong Entity Set- A strong entity set is an entity set that contains sufficient attributes to uniquely identify all its entities. In other words, a primary key exists for a strong entity set. Primary key of a strong entity set is represented by underlining it.
How can we identify weak entity?
What is an example of a weak entity?
Example for weak entity In the ER diagram, we have two entities building and apartment; Building is a strong entity because it has a primary key attribute called building number which is capable of uniquely identifying all the flats present in the apartment ; Unlike building, apartment is weak entity because it does not have any primary key and door number here acts only as a discriminator
What is the difference between weak entity and strong entity?
A weak entity is an entity set that cannot be uniquely identified by its attributes alone.
Why do weak entities always have total participation?
Every weak entity has no existence without the entity it is related to. Its weak in itself so as to identify independently . So it requires a corresponding or related strong entity which is independent. As each weak entity have its corresponding strong entity , all entity gets participated in relation giving a total participation.
Could you have an example of a weak entity?
Typically, a weak entity has a primary key that contains only one foreign key. The entity DEPENDENT, for example, is a weak entity because it uses the primary key of the EMPLOYEE entity as part of its own primary key. How can you tell if a entity is strong or weak? Difference between Strong and Weak Entity: Strong entity always has a primary key.