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why do we need weak entity in database when we can make it strong entity?
The table that has primary key is strong entity and the table that has no primary key is weak entity
weak the GDP in billions is $56.83
strong
Strong Weak opportunities threat
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?
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.
The table that has primary key is strong entity and the table that has no primary key is weak entity
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.
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.
An entity set may not have sufficient attributes to form a primary key is called weak entity set. One with primary key is called strong entity set.
In contrast to the strong or regular entity, a weak entity is one that meets two conditions: 1. The entity is existence-dependent; that is, it cannot exist without the entity with which it has a relationship. 2. The entity has a primary key that is partially or totally derived from the parent entity in the relationship.
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 .
Buffer systems. They convert strong acids or bases into weak acids or bases.
A weak entity can be identified uniquely only by considering the primary key of another (owner) entity.
weak entity