CODEWITHSUNDEEP
umlerd
Sheng IsBored
Sheng IsBored

Reputation: 51

UML: Multiplicity Concepts

My question is about UML multiplicity.i'm trying to understand the concept of multiplicity, for example, a person is allowed to have many cars but one car is for one person.if there are 2 class, person and car , it will be 1 to many and 1 to 1.However, in comparison to another example;a car and parts, 1 car will many many parts , which is 1 to many...how about parts to car ? is it 1:M as 1 part (screws) are used by many cars? or 1:1 cause that part is used only in 1 car ?

Upvotes: 0

Views: 344

Answers (2)

Gangnus
Gangnus

Reputation: 24474

There could different connections for the same pair of classes:

  • A person has a car - multiplicity is 1:(0..n), for one person can have several cars, any car has an owner.
  • A person drives a car - multiplicity is (0,1):(0,1), one person CAN drive a car, a car CAN be driven.
  • A person sits in a car - multiplicity is (0,n):(0,1), a person can sit in one car only. Car can hold 0-several people.

So, these two classes blocks will have three differently named connections, each with its own multiplicity.

You can have even more connections, for example, people that were killed by the car, people, person, who is repairing the car, person, who has rights to drive the car, and so on, depending on your task.

If you have many different connections, it will be more understandable to create a special class for every sort of connection.

But anyway, the pair of classes by itself does not define the sort of connection. For to set the connection you have to write down much more information.

Upvotes: 1

dat3450
dat3450

Reputation: 954

It is always advisable to think about instances of classes when trying to determine relationships between classes and cardinality. In this case, you have cars and parts. For example:

  • If you have one car (e.g. a red sedan), it will have a number of parts (e.g. an engine, a fuel tank, tyres, etc.)
  • If you have one item of a specific part (e.g. one engine), that can only be installed and belong to one car (e.g. the red sedan).

A car can have anywhere between one and many parts (1..M), and a part can only be installed in one car at most (0..1).

Hence the relationship between car and part is 1:M (using the maximums from each side as shown below).

--------                          --------
| Car  |  0..1  ----------  1..M  | Part |
--------                          --------

Upvotes: 1

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