Object Constraint Language

About OCL

• 
• side-effect free
• An Query Language
• To describe Guards
• To specify invariants, pre- & post-conditions

Constraint examples

• 
• context of the expression (attached to the UML model or specified explicitly)
• stereotype:inv, pre, post
• more examples:
  
  1. context Account
     inv: Account.allInstances()->forAll(a,b | a<>b implies a.accName<>b.accName)
     inv: Account.allInstances()->forAll(a | self<>a implies a.accName<>self.accName)
  2. invarient with let expressions:
     context Person inv:
     let income : Integer = self.job.salary->sum()
     let hasTitle(t: String) : Boolean = self.job->exists(title = t) in
     if isUnemployed then income < 100
     else income >= 100 and hasTitle('manager') endif
  3. Pre- and Post-conditions:
     context Person::income(d :Date):Integer
     pre : d.value >= self.job.startDate.value
     post :result =5000
  4. Attributes
     
  5. 
  6. Operations
  7. Association Ends and Navigation
     context Company inv :self.manager.isUnemployed =false inv :self.employee->notEmpty()
     context Person inv : self.employer->size()< 3
     Note:By default, navigation will result in a Set. When the association on the Class Diagram is adorned with {ordered}, the navigation results in a Sequence.
  8. Navigation over Association with Multiplicity zero or one
     context Person inv : self.wife->notEmpty()implies self.wife.sex =Sex::female
  9. Combining Properties
     [1] Married people are of age >= 18
     context Person inv :
     self.wife->notEmpty()implies self.wife.age >=18 and
     self.husband->notEmpty()implies self.husband.age >=18
  10. Navigation to Association Classes
  11. Navigation from Association Classes
      context Job
      inv :self.employer.numberOfEmployees >=1
      inv :self.employee.age >21
  12. Accessing overridden properties of supertypes
      context B inv :
      self.oclAsType(A).p1 --accesses the p1 property defined in A
      self.p1 --accesses the p1 property defined in B
  13. Navigating to collections:
      
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• The OCL Standard Library
• References:
  1. OCL-specificatin-v1.3a
  2. OCL Tutorial