CODEWITHSUNDEEP
umlclass-diagramuse-caseuse-case-diagrammultiplicity
KijeviGombooc
KijeviGombooc

Reputation: 342

Should I use n or * if I have exact number of things in the model?

I need to create UML diagrams for homework about a game ( called Downfall). I have to create it so that it works on any number (n) of player.

If this is an exact number that appears in multiple places of the diagram, should I use n or *? I would use it in multiplicity parameters and in size of array.

For example: There are n sides, and if there is a dial on a side, there has to be dial on each side at that position, so the dial has n-1 connected dials.

Upvotes: 2

Views: 1206

Answers (2)

www.admiraalit.nl
www.admiraalit.nl

Reputation: 6089

According to the UML specification, n is syntactically a valid multiplicity (see Ister's answer), but to make sure it is also semantically correct, you would have to define the meaning of n somewhere. Usually, n is not used as a multiplicity in UML diagrams.

I would advise you to use * in this case. If the minimum number of players is 2, you may use 2..*.

Additionally, you may use notes or constraints, e.g. { the number of connected dials is equal to the number of sides minus one }. You may also use a formal constraint language, like OCL.

Upvotes: 1

Ister
Ister

Reputation: 6318

TL;DR

You can use a constant, like n. I would though recommend using a self-explanatory constant name like numberOfPlayers or at least noOfPlayers to make it obvious that it is always the same constant.

The name of the constant should be written without quotes (to distinguish it from strings, which are presented in double-quotes).

You can also use expression like n-1 as long as it evaluates to a non-negative Integer all the time.

Full explanation

Let's go by the UML specification. All section and figure references are from it.

1. Multiplicity definition (7.5.3.2)

The multiplicity is defined as lowerValue and upperValue.

The lower and upper bounds for the multiplicity of a MultiplicityElement are specified by ValueSpecifications (see Clause 8), which must evaluate to an Integer value for the lowerBound and an UnlimitedNatural value for the upperBound (see Clause 21 on Primitive Types)

2. ValueSpecification definition

ValueSpecification is defined as either LiteralSpecification (8.2) or Expression or OpaqueExpression (both described in 8.3).

LiteralSpecification is essentially just a number in the case interesting for us, so it is not what you need. But it is not the only option as www.admiraalit.nl suggests in his answer.

3. Expression definition (8.3.3.1)

An Expression is a mechanism to provide a value through some textual representation and eventually computation (I'm simplifying here). For instance:

An Expression is evaluated by first evaluating each of its operands and then performing the operation denoted by the Expression symbol to the resulting operand values

If you use a simple expression without operands, it simply becomes a constant that is a template for your model. So feel free to use a constant as a multiplicity value, as long as the constant evaluates to non-negative Integer (or UnlimitedNatural in case of an upper Limit).

It may even be an expression that changes its value over the lifecycle of the object however ensuring that this kind of multiplicity is met all the time might become challenging.

Upvotes: 5

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