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.
**************
Go to Important Keywords/Terms in DBMS page
Go to Total participation page
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
No comments:
Post a Comment