What is optional relationship?

What is optional relationship?

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 kind of relationships can tables have between each other?

There are three specific types of relationships that can exist between a pair of tables: one-to-one, one-to-many, and many-to-many. The tables participate in only one type of relationship at any given time.

How do you break a many-to-many relationship between tables?

To avoid this problem, you can break the many-to-many relationship into two one-to-many relationships by using a third table, called a join table. Each record in a join table includes a match field that contains the value of the primary keys of the two tables it joins.

What is mandatory and optional relationships?

In a mandatory relationship, every instance of one entity must participate in a relationship with another entity. In an optional relationship, any instance of one entity might participate in a relationship with another entity, but this is not compulsory.

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.

When to use optionality in relational database design?

Entity-relationship notation for the Student-Class relationship, with optionality shown at the Class side.

Is it necessary to know the optionality of a relationship?

It can be useful to know one additional piece of information about a relationship. This is what’s called the relationship’s optionality. This information is not strictly necessary for a complete ERD, but it can be very useful information to gather. Cardinality allows you to answer the question “How many?”