Contents
What does a ternary relationship refer to?
A ternary relationship is an association among three entities. This type of relationship is required when binary relationships are not sufficient to accurately describe the semantics of the association. The ternary relationship construct is a single diamond connected to three entities as shown in Figure 2.3.
Is ternary a degree of relationship?
Ternary Relationship: a ternary relationship is a relationship of degree three. That is, a relationship that contains three participating entities. The cardinality constraint of an entity in a ternary relationship is defined by a pair of two entity instances associated with the other single entity instance.
What is aggregation in DBMS?
Aggregation in DBMS Aggregation refers to the process by which entities are combined to form a single meaningful entity. The specific entities are combined because they do not make sense on their own. To establish a single entity, aggregation creates a relationship that combines these entities.
Why did the ER model needed?
An entity-relationship diagram, or ER diagram, is essential for modeling the data stored in a database. It is the basic design upon which a database is built. ER diagrams specify what data we will store: the entities and their attributes. They also show how entities relate to other entities.
What is relationship called when it is maintained between two entities?
Explanation: Ellipse represents attributes, rectangle represents entity. 6. What is a relationship called when it is maintained between two entities? Explanation: Primary key of one relation used as an attribute in another relation is called foreign key.
How do you show a ternary relationship?
In Ternary relationship three different Entities takes part in a Relationship. For Example: Consider a Mobile manufacture company….Three different entities involved:
- Mobile – Manufactured by company.
- Part – Mobile Part which company get from Supplier.
- Supplier – Supplier supplies Mobile parts to Company.
What is cardinality of a relationship?
Relationship cardinality represents the fact that each parent entity or table within a relationship is connected to a particular number of instances of the child entity or table. Each parent in the relationship is connected to one or more instances of the child entity or table.
Which database is good for aggregation?
Oracle, DB2 Warehouse edition, and to a lesser degree SQLServer enterprise are all very good on these aggregate queries — of course these are expensive solutions and it depends very much on your budget and business case whether its worth it.