What are weak entity sets in DBMS?
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 weak entity set 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. I don’t understand why this is accepted, it’s simply wrong.
What are weak entity types?
An entity type should have a key attribute which uniquely identifies each entity in the entity set, but there exists some entity type for which key attribute can’t be defined. These are called Weak Entity type.
What are strong and weak entity set Explain with suitable example?
Unlike a strong entity, a weak entity does not have any primary key….Difference between Strong and Weak Entity:
| S.NO | Strong Entity | Weak Entity |
|---|---|---|
| 1. | Strong entity always has a primary key. | While a weak entity has a partial discriminator key. |
| 3. | Strong entity is represented by a single rectangle. | Weak entity is represented by a double rectangle. |
Why weak entity sets are needed?
Why, then, do we have weak entity sets? Answer :We have weak entities for several reasons: We want to avoid the data duplication and consequent possible inconsistencies caused by duplicating the key of the strong entity. Weak entities reflect the logical structure of an entity being dependent on another entity.
What are weak entity sets in DBMS Mcq?
If an entity set does not have enough attributes to form a primary key, it is called a weak entity set. Explanation: In E-R diagram, the many-to-one relationship with a weak entity set is represented by diamond with double borders.
What is the difference between weak and strong entity set?
A strong entity is represented by single rectangle. A weak entity is represented by double rectangle. Relationship between two strong entities is represented by single diamond. Relationship between a strong and weak entity is represented by double diamond.
What is weak entity set and strong entity set?
What are strong and weak entity sets in DBMS?
The strong entity has a primary key. Weak entities are dependent on strong entity. Its existence is not dependent on any other entity. Continuing our previous example, Professor is a strong entity here, and the primary key is Professor_ID.
Why do we use weak entity sets?
Weak entity set is required for following reasons: 1. To avoid the inconsistencies caused by duplicating the key of the strong entity.
Why do we have weak entity sets?
What are strong and weak entity explain?
In the ER diagram, we have two entities Employee and Dependents. Employee is a strong entity because it has a primary key attribute called Employee number (Employee_No) which is capable of uniquely identifying all the employee. Unlike Employee, Dependents is weak entity because it does not have any primary key .
Why do we need weak entity set?
How can a weak entity set be strong?
We can convert any weak entity set to a strong entity set by simply adding appropriate attributes.
Does weak entity have primary key?
An entity with a primary key is strong entity. An entity that does not have primary key is weak entity. The discrimination of a weak entity set is a set of attributes tat serves to distinguish among entities in the entity set that depend on one particular strong entity.
What is weak entity set when does it happen?
An entity is weak when two conditions are met: The entity is existence-dependent on another entity. The entity gets at least part of its primary key from that other entity.
What is weak entity in DBMS?
A weak entity is an entity set that does not have sufficient attributes for Unique Identification of its records. Simply a weak entity is nothing but an entity which does not have a primary key attribute. It contains a partial key called as discriminator which helps in identifying a group of entities from the entity set.
What is the primary key of a weak entity set?
The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent plus the weak entity sets discriminator. In the above example {loan_number, payment_number} acts as primary key for payment entity set.
What is a strong entity set in Entity Framework?
A Strong Entity Set is defined as an entity set that contains sufficient attributes to uniquely identify all its entities. In general, a primary key exists for a Strong Entity Set. The primary key of a Strong Entity Set is represented by simply underlining it.
What is the discriminator of a weak entity set?
The discriminator of a weak entity set is a set of attributes that allows this distinction be made. For example, payment_number acts as discriminator for payment entity set. It is also called as the Partial key of the entity set.