2 Answers. Associative entities are used when you need a relationship to
be involved
in a relationship. For a normal many-to-many relationship between Student and Course , we would use just a diamond. However, if we want to associate Enrollment with Teacher , we can turn Enrollment into an associative entity.
What is an example of associative entity?
Manually this can be handled by creating a mutual entity between the two entities, which is called an associative entity. … For example, if
the key of A was 1 and the key of B was 2
, then the key of the associative entity AB would be 1, 2.
What is an associative entity explain how is it created?
An associative entity is a term used in relational and entity–relationship theory. A relational database
requires the implementation of a base relation (or base table) to resolve many-to-many relationships
. A base relation representing this kind of entity is called, informally, an associative table.
What does an associative entity do?
Associative entities are connections that describe a relationship between two different entities. … Associative entities
convey information about their attributes and their connections
. They are considered an entity because they have attributes, and they are considered a relationship because they link entities together.
What role do associative entities play join tables in many-to-many joins?
An associative entity is the table that associates
two other tables in a many to many relationship
. An associative relationship attribute is an attribute of the associative entity that exists because of the many to many relationship.
What are strong entities?
Strong Entity:
A strong entity is
not dependent on any other entity in
the schema. … Strong entities are represented by a single rectangle. The relationship of two strong entities is represented by a single diamond. Various strong entities, when combined together, create a strong entity set.
When should a relationship be converted to an associative entity?
Associative entities are used when you need a relationship to be involved in a relationship. For a normal many-to-many relationship between Student and Course , we would use just a diamond. However, if we want
to associate Enrollment with Teacher
, we can turn Enrollment into an associative entity.
What is an example of a many-to-many relationship?
A many-to-many relationship occurs when multiple records in a table are associated with multiple records in another table. For example, a many-to-many relationship exists
between customers and products
: customers can purchase various products, and products can be purchased by many customers.
Can an associative entity have a primary key?
An associative entity has
the same primary key as its supertype associative entity
, and this primary key is also a foreign key to the supertype associative entity.
How is a strong entity different from a weak entity?
Strong entity is independent of other entities.
Weak entity is dependent on strong entity
. A strong entity is represented by single rectangle. A weak entity is represented by double rectangle.
What is weak entity 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.
How can we identify weak entity in ER diagram?
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.
How do you implement many-to-many relationships?
A relationship is many-to-many if and only if one record from table A is related to one or more records in table B and vice-versa. To establish a many-to-many relationship, create a
third table called “ClassStudentRelation”
which will have the primary keys of both table A and table B.
What is the problem with many-to-many relationship?
The problem with many-to-many relationships is that
it can cause duplications in the returned datasets
, which can result in incorrect results and might consume excessive computing resources.
What do we generally avoid in many-to-many junction table?
This many-to-many junction table is just a name used in theory for relational & entity–relationship type table.
No direct connection should be established
, and an attempt should be made to have communications via multiple points so that if one fails, the other should be able to cover up the loose connections.
