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What is optional relationship in database?
An optional relationship between two entities indicates that it is not necessary for every entity occurrence to participate in the relationship. In other words, for both entities the minimum number of instances in which each participates, in each instance of the relationship is zero (0).
What is optional database?
Continuing with the language of tables to distinguish between mandatory and optional relationships, an optional relationship exists for a table when there is no requirement for any records to exist in that table before any records can be added to the associated table.
What is the relationship between optional mandatory relationship and minimum cardinality?
If minimum cardinality of a relationship equals 0 then participating in a relationship is optional. If minimum cardinality of a relationship equals n then at least n instances must be mapped to one instance of A.
What is mandatory and compulsory?
The word ‘mandatory’ is generally used in the sense of ‘binding’. On the other hand, the word ‘compulsory’ is generally used in the sense of ‘essential’. This is the main difference between the two words. It is important to note that anything that is mandatory has the quality of binding the doer to the work.
What is minimum and maximum cardinality?
A: You are correct in noticing that maximum cardinality is a more important characteristic of a relationship than minimum cardinality is. All minimum cardinality tells you is the minimum allowed number of rows a table must have in order for the relationship to be meaningful.
What is mandatory in relationship?
If the relationship is required (mandatory), then the |0 at the end of the line changes to || (one and only one). We use mandatory relationships when we don’t want an occurrence of an entity to be store in the database unless it is related to an occurrence of the entity at the other end of the relationship.
When does an optional relationship exist in a table?
Describe optional participation in relationships. Continuing with the language of tables to distinguish between mandatory and optional relationships, an optional relationship exists for a table when there is no requirement for any records to exist in that table before any records can be added to the associated table.
What does optional participation mean in database design?
[5] optional participation: In the language of database design, participation refers to the nature of the relationship between tables. Optional participation describes a relationship in which no records need to exist in a table before records are added to its associated table.
How is optional participation used in a 1 : 1 relationship?
In a 1:1 relationship, if one entity has optional participation and the other has mandatory participation, the weak entity (the entity with optional participation) receives the key attribute from the mandatory entity to establish the link.
What does mandatory entity mean in relational database?
[1] mandatory entity: In the language of relational database design, mandatory entity is another name for the entity that has mandatory participation in an entity relationship. [2] mandatory participation: In the language of database design, participation describes the nature of the relationship between two tables.