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Describes the several relationship constraints through giving suitable example?
Constraints on relationships: There are two kinds of constraints on relationships.
1) Mapping cardinalities or cardinality ratios express the number of entities to that another entity can be associated through a relationship set. For a binary relationship set among entities A and B. The mapping cardinality may be any one of the subsequent:
a) One to One: An entity in A is related along with at most one entity in B and an entity in B is related with at most one entity in A.b) One to Many: An entity in A can be related with any number in B but an entity in B is associated with at most one in A.c) Many to one: An entity in A is related with at most one in B but an entity in B is associated with any number in A.d) Many to Many: An entity in A and B can be associated along with any number of entities in the other entity set.
2) Participation constraints: The participation of an entity set E in a relationship set R is said to be total if every entity in E participates within at least one relationship in R. If only a few entities in E participation of entity set E in relationship R is said to be partial.
What does the cardinality ratio specify? Mapping cardinalities or cardinality ratios state the number of entities to which another entity can be associated. Mapping cardinaliti
Describe the functions and features of foreign key? Foreign Key : The primary key of one file or table that is implanted in another file or table to implement the relationships
explain participation constraints with examples
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When a function module is activated syntax checking is performed automatically. YEs, a function module is activated syntax checking.
What is called an evaluation primitive? A relational algebra operation annotated with instructions on how to evaluate is known as an evaluation primitive.
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