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What do you mean by referral integrity constraints ?
What else can I help you with?
Difference between entity and entity set?
Entity - Table Entity Set - Rows in Table
Explain the difference between a weak and a strong entity set?
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.
Can weak entity be converted into strong entity in DBMS?
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.
Difference between entity type and entity set?
lets understand them all: 1.An Entity is a real world "thing" which have independent existence. 2.Entity type is a category. 3.entity type is strictly calling, "an instance of entity type". 4.An entity type defines a collection of entities that have the same attributes. 5.Entity set : the collection of all entities of a particular entity type in the database at any point of time is called Entity set.
Difference between an entity set and an entity instance?
An entity set is a collection of similar entities that share common attributes, representing a specific concept within a database, such as "Students" or "Employees." In contrast, an entity instance refers to a single, specific occurrence of an entity within that set, encompassing the actual data for a particular individual, like "John Doe" or "Employee ID 12345." Essentially, an entity set is a blueprint or template, while entity instances are the concrete realizations of that blueprint.
Can weak entity be converted into strong entity?
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.
What is strong and weak entity set?
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.
What are 10 cardinalities appropriate for ERD?
In an Entity-Relationship Diagram (ERD), cardinalities define the relationships between entities. Common cardinalities include: One-to-One (1:1) - Each entity in set A is related to one entity in set B and vice versa. One-to-Many (1:N) - An entity in set A can relate to multiple entities in set B, but an entity in set B relates to only one in set A. Many-to-One (N:1) - Multiple entities in set A can relate to one entity in set B. Many-to-Many (M:N) - Entities in set A can relate to multiple entities in set B and vice versa. Zero or One (0..1) - An entity may or may not have a relationship with another entity. Zero or Many (0..N) - An entity can have no relationship or many relationships with another entity. Exactly One (1) - An entity must have exactly one relationship with another entity. At Least One (1..N) - An entity must have at least one relationship but can have many. At Most One (0..1) - An entity can have no relationship or one relationship, but not more. Optional (0..M) - An entity may have zero or more relationships with another entity. These cardinalities help in modeling the data structure and understanding the interactions between different entities.
What is entity classes?
same as entity class or entity type or entity set
A relationship between the instances of a single entity type is called a ........................?
A relationship between instances of a single entity type is called a self-relationship or recursive relationship. This type of relationship occurs when an entity is related to other instances of the same entity type within the same entity set.
What is an extension of an entity type?
its an set of entity
What is weak entity sets in dbms?
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.
