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All DBMS Interview Questions
31. What is Cardinality ratio?
Ans: The cardinality ratio for a binary relationship specifies the number of relationship instances that an entity can participate in.
32. What is a Participation constraint?
Ans: The participation constraint specifies whether the existence of an entity depends on its being related to another entity via the relationship type. This is of two types:
1. Total participation.
2. Partial participation.
33. What is a weak entity types?
Ans: The entity types that do not have key attributes of their own are called weak entity types.
Rests are called strong entity types .The entity that gives identity to a weak entity is called owner entity. And the relationship is called identifying relationship. A weak entity type always has a total participation constraint with respect to its identifying relationship.
34. What is an ER Diagram?
Ans:
This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
35. What is an EER?
Ans:
==
36. What is specialization?
Ans: It is the process of defining a set of subclasses of an entity type where each subclass contain all the attributes and relationships of the parent entity and may have additional attributes and relationships which are specific to itself.
37. What is generalization?
Ans: It is the process of finding common attributes and relations of a number of entities and defining a common super class for them.
38. What are constraints on generalization and specialization?
Ans:
1. disjoint ness constraints.
2. Completeness constraints.
Disjointness constraint specifies that the subclasses of the specialization must be disjoint .i.e. an entity can be a member of at most one of the subclasses of the specialization. The reverse of it is overlapping.
Completeness constraint is a participation constraint which may be
1. Total
2. Partial
Total specialization constraint tells that each entity in the super class must be a member of some subclass in the specialization. And partial specialization constraint allows an entity not to belong to any of the subclasses .Thus we do have the following 4 types of constraints on specialization:
1. Disjoint, total
2. Disjoint, partial
3. Overlapping, total
4. Overlapping, partial
39. What is a ternary relationship?
Ans: A relationship with a degree 3 is called a ternary relationship.
40. What is aggregation and association?
Ans: Aggregation is an abstraction concept for building composite objects from their component objects. The abstraction of association is used to associate objects from several independent classes.
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