Multiplicity Constraints in Signature Declaration

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Multiplicity Constraints in Signature Declaration

• By Leon Hsuwei Kao Kevin Pak Kwan Chan

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From Previous Presentation

• From previous presentation given by Sanjev and
  Thiranjith. There are multiplicity constraint
  keywords
• lone for 0 or 1
• one for exactly 1
• set for 0 or more
• However, there is also another multiplicity
  keyword
• some for 1 or more

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Question...

• Question How can we define a specific number for
  the multiplicities?
• For example
• 2 or more,
• 3 or less,
• Between 4 and 5

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Example

• Lets consider the example Father and child.
  (Not being sexist here)
• Everybody has a father
• sig Person
• father lone Father
• Every father has zero or more children
• sig Father extends Person
• children some Person

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Example continues

• If a person is a child of someone, then that
  someone is the persons father
• //symmetric relations
• fact all fFather, c f.children c.father f
  

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Constraints

• A Father cannot be a child of its children
• //non reflective transitive closure
• fact no fFather f in f.children
• A Person cannot be a father of its ancestor
• //non reflective transitive closure
• fact no pPerson p in p.father

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Example

• For example, some law got passed that say you
  cannot have more than 2 children otherwise the
  newborns will be killed for population control.