Thursday, 12 April 2018

Define partial participation in ER model

Define partial participation in ER model





Participation constraints

Participation constraints deal with the participation of entities from an entity set in a relationship set. Participation constraint is sometimes referred as minimum cardinality constraint.

Partial participation

If only some entities of an entity set participate in a relationship, then this situation is called as partial participation. And total participation in ERD is shown with double line (link) between the entity set and the relationship set.

Example 1:

Let us consider a database to store data about entity sets Owner, Car, and Bike. Also, let us assume the following conditions;
  • An owner can have one or more cars or bikes or both
  • A car can have one or more owners
  • A bike can have one or more owners
The following ER diagram shows the database with three entity sets Owner, Car, Bike and two relationship sets Car_Owner and Bike_Owner for the given requirement.


 
In this ERD, it is not compulsory for an owner to have a car or bike. He may have a car or bike or both. So, there may a owner who has a car but not a bike. That means that owner entity is participated in Car_Owner relationship but not in Bike_Owner relationship. Hence, the participation of Owner entity set on either Car_Owner or Bike_Owner relationships are partial.

On the other hand, for a car entity or a bike entity to exist then there should be an owner related to them. That is, each bike to be stored in Bike relation must have at least one owner. The same is applicable for Car also. Hence, the participation of Car on Car_Owner and Bike on Bike_Owner relationships are Total.

Example 2:

Consider a database for storing student details, their extra-curricular activities and the course details. To model this database, we need three entity sets. If we have to link these entity sets, then we can link STUDENT with both EXTRACURRICULAR and COURSE. In this case, all students must have course details but not extra-curricular details as it is not mandatory to participate in any extra-curricular activities. Hence, the participation of EXTRACURRICULAR entity set in the relationship between STUDENT and itself is partial.  

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What is partial participation in database?
Define partial participation in ER modelling
Example ERD for partial participation
Purpose of partial participation in ER model
Advantage of partial participation
participation constraints in ER model
difference between total and partial participations

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