1. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 1 Object Constraint Language (OCL) Yih-Kuen Tsay Dept. of Information Management National Taiwan University

2. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 2 Outline Introduction Relation with UML Models Basic Values and Types Objects and Properties Collection Operations

3. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 3 About OCL A formal language for writing expressions (such as invariants) on UML models. It can also be used to specify queries. OCL expressions are pure specifications without side effects. OCL is a typed language. Version 2.0 still in the finalization process (though main part of UML 2.0 has been finalized).

4. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 4 Why OCL UML diagrams do not provide all the relevant aspects of a specification. Additional constraints expressed by a natural language are ambiguous. Traditional formal languages are precise, but hard to use. OCL tries to be formal and yet easy to use.

5. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 5 Where to Use UML As a query language Invariants on classes and types. Pre- and post-conditions on operations Guards Target sets for messages and actions Constraints on operations Derivation rules for attributes

6. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 6 Basic Form context TypeName inv: 'this is an OCL expression with stereotype > in the context of TypeName' = 'another string'

7. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 7 Class Diagram Example

8. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 8 Relation with UML Models Each OCL expression is written in the context of an instance of a specific type. The reserved word self is used to refer to the contextual instance. An explicit context declaration can be omitted if the OCL expression is properly placed in a diagram.

9. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 9 Invariants Inside the class diagram example: self.numberOfEmployees > 50 specifies that the number of employees must always exceed 50. Alternatively, context Company inv: self.numberOfEmployees > 50 A different name can be used for self : context c : Company inv: c.numberOfEmployees > 50 The invariant itself can also be given a name (after inv).

10. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 10 Pre- and Post-Condtions Basic form: context Typename::operationName(param1 : Type1,... ): ReturnType pre : param1 >... post: result =...

11. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 11 Pre- and Post-Condtions (cont.) Example: context Person::income(d : Date) : Integer post: result = 5000 Names may be given: context Typename::operationName(param1 : Type1,... ): ReturnType pre parameterOk: param1 >... post resultOk : result =...

12. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 12 Package Context package Package::SubPackage context X inv:... some invariant... context X::operationName(..) pre:... some precondition... endpackage

13. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 13 Operation Body Expression context Person::getCurrentSpouse() : Person pre: self.isMarried = true body: self.mariages->select( m | m.ended = false ).spouse

14. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 14 Initial and Derived Values context Person::income : Integer init: parents.income->sum() * 1% -- pocket allowance derive: if underAge then parents.income->sum() * 1% -- pocket allowance else job.salary -- income from regular job endif

15. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 15 Basic Types Boolean: true, false Integer: 1, -5, 2, 34, 26524,... Real: 1.5, 3.14,... String: 'To be or not to be...'

16. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 16 Basic Operations Integer: *, +, -, /, abs() Real: *, +, -, /, floor() Boolean: and, or, xor, not, implies, if-then- else String: concat(), size(), substring()

17. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 17 Other Types Classifiers –All classifiers of a UML model are types in its OCL expressions. Enumerations

18. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 18 Sub-expressions context Person inv: let income : Integer = self.job.salary->sum() in if isUnemployed then income < 100 else income >= 100 endif

19. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 19 Definition Expressions context Person def: income : Integer = self.job.salary->sum() def: nickname : String = ’Little Red Rooster’ def: hasTitle(t : String) : Boolean = self.job- >exists(title = t)

20. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 20 More about Types and Operations Type conformance Casting (re-typing) Precedence rules Infix operators Keywords Comments

21. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 21 Properties A property is one of An Attribute context Person inv: self.age > 0 An AssociationEnd An Operation with isQuery A Method with isQuery

22. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 22 Previous Values in Post-Conditions context Person::birthdayHappens() post: age = age@pre + 1 context Company::hireEmployee(p : Person) post: employees = employees@pre->including(p) and stockprice() = stockprice@pre() + 10

23. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 23 Previous Values in Post-Conditions (cont.) a.b@pre.c -- takes the old value of property b of a, say x -- and then the new value of c of x. a.b@pre.c@pre -- takes the old value of property b of a, say x -- and then the old value of c of x.

24. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 24 Collections Set Bag OrderedSet Sequence

25. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 25 Collection Operations Select context Company inv: self.employee->select(age > 50)->notEmpty() Reject context Company inv: self.employee->reject( isMarried )->isEmpty()

26. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 26 ForAll Operation context Company inv: self.employee->forAll( age <= 65 ) inv: self.employee->forAll( p | p.age <= 65 ) inv: self.employee->forAll( p : Person | p.age <= 65 ) context Company inv: self.employee->forAll( e1, e2 : Person | e1 <> e2 implies e1.forename <> e2.forename)

27. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 27 Exists Operation context Company inv: self.employee->exists( forename = 'Jack' ) context Company inv: self.employee->exists( p | p.forename = 'Jack' ) context Company inv: self.employee->exists( p : Person | p.forename = 'Jack' )

28. IM NTU Software Development Methods, Fall2006 Software Development Methods, Fall 2006 OCL 2006/12/07 -- 28 Iterate Operation Reject, Select, forAll, Exists, and Collect can all be described in terms of interate. Example: collection->collect(x : T | x.property) -- is identical to: collection->iterate(x : T; acc : T2 = Bag{} | acc->including(x.property))