An entity set that does not possess sufficient attributes to form a primary key is called a weak entity set. One that does have a primary key is called a strong entity set.
The discriminator (or partial key) of a weak entity set is the set of attributes that distinguishes among all the entities of a weak entity set
The existence of a weak entity set depends on the existence of a identifying entity set. It must relate to the identifying entity set via a total, one-to-many relationship set from the identifying to the weak entity set
We depict a weak entity set by double rectangles in E-R diagram. We underline the discriminator of a weak entity set with a dashed line in E-R diagram.
strong entity : in this the attributes must have values for instance . weak entity : in this the attributes may or may not have values for instance .
What is the difference between strong and brave
A regular entity, also known as a strong entity, has a primary key that uniquely identifies each instance and can exist independently of other entities. In contrast, a weak entity does not have a sufficient primary key and relies on a "strong" or "regular" entity for its identification; it is dependent on the strong entity for its existence and typically has a partial key. Weak entities are often used to represent a relationship that requires more context, while regular entities stand alone as distinct objects in a database.
the enitity which is set primary key is said to be strong entity and the entity which does not set primary key is said to be weak entity.
A weak entity set can always be make into strong entity set by adding to its attribute of its identifying entity set. For a weak entity set, we add columns to the table corresponding to the primary key of the strong entity set on which the weak set is dependent.
why do we need weak entity in database when we can make it strong entity?
To convert a weak entity to a strong entity, you can assign it a primary key that uniquely identifies each instance of the weak entity, rather than relying on the primary key of its associated strong entity. This often involves creating a new attribute or a combination of attributes within the weak entity itself to serve as the primary key. Additionally, you may need to remove the dependency on the strong entity's key, ensuring the weak entity can exist independently. Lastly, update the database schema to reflect these changes.
The table that has primary key is strong entity and the table that has no primary key is weak entity
Nationalism involves a strong identification of a group of individuals with a political entity defined in national terms, i.e. a nation. Often, it is the belief that an ethnic group has a right to statehood.
what is the answer
The primary key of a weak entity set is formed by taking the primary key of the strong entity set on which its existence depends (see Mapping Constraints) plus its discriminator. A strong entity set has a primary key. All tuples in the set are distinguishable by that key. A weak entity set has no primary key unless attributes of the strong entity set on which it depends are included. Tuples (a particular row) in a weak entity set are partitioned according to their relationship with tuples in a strong entity set. Tuples within each partition are distinguishable by a discriminator, which is a set of attributes.
When there is a great difference in air pressure between two areas, winds are strong. The air moves from high pressure to low pressure, causing faster winds to equalize the pressure difference.