21. What do you mean by domain value or value set of an attribute?
Ans: Friends it is the set of values that may be assigned to that attribute for each individual entities.

22. What do you mean by degree of a relationship?
Ans: Friends the no of entities participating in that relation.

23. What do you mean by recursive relationship?
Ans: Friends It is the relationship where both the participating entities belong to same entity type.

24. What are relationship constraints?
Ans: Friends
1. Cardinality ratio.
2. Participation constraints.

25. What do you mean by Cardinality ratio?
Ans: Friends the cardinality ratio for a binary relationship specifies the number of relationship instances that an entity can participate in.

26. What do you mean by a Participation constraint?
Ans: Friends 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.

27. What do you mean by a weak entity types?
Ans: Friends 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.

28. What do you mean by an ER Diagram?
Ans: Friends 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.

29. What do you mean by an EER?
Ans: Friends EER Is Energy Efficiency Ratio

30. What do you mean by specialization?
Ans: Friends 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.