im ntu software development methods, fall2004 software development methods, fall 2004 ocl -- 1...

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OCLOCL -- -- 11Software Development Methods, FallSoftware Development Methods, Fall 20042004

Object Constraint Object Constraint LanguageLanguage

(OCL)(OCL)

Yih-Kuen TsayYih-Kuen Tsay

Dept. of Information Dept. of Information ManagementManagement

National Taiwan UniversityNational Taiwan University

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OutlineOutline

► IntroductionIntroduction►Relation with UML ModelsRelation with UML Models►Basic Values and TypesBasic Values and Types►Objects and PropertiesObjects and Properties►Collection OperationsCollection Operations

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About OCLAbout OCL

►A A formalformal language for writing language for writing expressionsexpressions (such as invariants) on (such as invariants) on UML models.UML models.

► It can also be used to specify It can also be used to specify queriesqueries..►OCL expressions are pure OCL expressions are pure

specifications specifications without side effectswithout side effects..►OCL is a typed language.OCL is a typed language.►Version 2.0 in the finalization process.Version 2.0 in the finalization process.

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Why OCLWhy OCL

►UML diagrams do not provide all the UML diagrams do not provide all the relevant aspects of a specification.relevant aspects of a specification.

►Additional constraints expressed by a Additional constraints expressed by a natural language are ambiguous.natural language are ambiguous.

►Traditional formal languages are Traditional formal languages are precise, but hard to use.precise, but hard to use.

►OCL tries to be formal and yet easy OCL tries to be formal and yet easy to use.to use.

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Where to Use UMLWhere to Use UML

► As a query languageAs a query language► Invariants on classes and types.Invariants on classes and types.► Pre- and post-conditions on operationsPre- and post-conditions on operations►GuardsGuards► Target sets for messages and actionsTarget sets for messages and actions► Constraints on operationsConstraints on operations►Derivation rules for attributesDerivation rules for attributes

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Basic FormBasic Form

context TypeName inv:'this is an OCL expression with stereotype <

<invariant>> in thecontext of TypeName' = 'another string'

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Class Diagram ExampleClass Diagram Example

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Relation with UML ModelsRelation with UML Models

►Each OCL expression is written in the Each OCL expression is written in the contextcontext of an instance of a specific of an instance of a specific type.type.

►The reserved word The reserved word selfself is used to refer is used to refer to the contextual instance.to the contextual instance.

►An explicit context declaration can be An explicit context declaration can be omitted if the OCL expression is omitted if the OCL expression is properly placed in a diagram.properly placed in a diagram.

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InvariantsInvariants

► Inside the class diagram example:self.numberOfEmployees > 50specifies 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).

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Pre- and Post-CondtionsPre- and Post-Condtions►Basic form:

context Typename::operationName(param1 : Type1, ... ): ReturnTypepre : param1 > ...post: result = ...

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Pre- and Post-Condtions (cont.)Pre- and Post-Condtions (cont.)►Example:

context Person::income(d : Date) : Integerpost: result = 5000

► Names may be given:Names may be given:context Typename::operationName(param1 : Type1, ... ): ReturnTypepre parameterOk: param1 > ...post resultOk : result = ...

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Package ContextPackage Context

package Package::SubPackagecontext X inv:... some invariant ...context X::operationName(..)pre: ... some precondition ...endpackage

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Operation Body ExpressionOperation Body Expression

context Person::getCurrentSpouse() : Person

pre: self.isMarried = truebody: self.mariages->select( m | m.ended =

false ).spouse

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Initial and Derived ValuesInitial and Derived Values

context Person::income : Integerinit: parents.income->sum() * 1% -- pocket allowancederive: if underAgethen parents.income->sum() * 1% -- pocket allowanceelse job.salary -- income from regular jobendif

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Basic TypesBasic Types

►Boolean: true, false►Integer: 1, -5, 2, 34, 26524, ...►Real: 1.5, 3.14, ...►String: 'To be or not to be...'

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Basic OperationsBasic Operations

►Integer: *, +, -, /, abs()►Real: *, +, -, /, floor()►Boolean: and, or, xor, not, implies, if-then-

else►String: concat(), size(), substring()

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Other TypesOther Types

►Classifiers All classifiers of a UML model are types in its O

CL expressions.►Enumerations

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Sub-expressionsSub-expressions

context Person inv:let income : Integer = self.job.salary->sum()

inif isUnemployed thenincome < 100elseincome >= 100endif

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Definition ExpressionsDefinition Expressions

context Persondef: income : Integer = self.job.salary->sum()def: nickname : String = ’Little Red Rooster’def: hasTitle(t : String) : Boolean = self.job->exists

(title = t)

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More about Types and More about Types and OperationsOperations►Type conformanceType conformance►Casting (re-typing)Casting (re-typing)►Precedence rulesPrecedence rules► Infix operatorsInfix operators►KeywordsKeywords►CommentsComments

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PropertiesProperties

A property is one ofA property is one of►An AttributeAn Attribute

context Person inv:self.age > 0

►An AssociationEndAn AssociationEnd►An Operation with An Operation with isQueryisQuery►A Method with A Method with isQueryisQuery

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Previous Values in Post-Previous Values in Post-ConditionsConditions► context Person::birthdayHappens()

post: age = age@pre + 1► context Company::hireEmployee(p : Person)

post: employees = employees@pre->including(p) andstockprice() = stockprice@pre() + 10

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Previous Values in Post-Conditions Previous Values in Post-Conditions (cont.)(cont.)[email protected] -- takes the old value of property

b of a, say x-- and then the new value of c of x.

[email protected]@pre -- takes the old value of property b of a, say x

-- and then the old value of c of x.

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CollectionsCollections

►SetSet►BagBag►OrderedSetOrderedSet►SequenceSequence

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Collection OperationsCollection Operations

►Select Select context Company inv:self.employee->select(age > 50)->notEmpty()

►RejectRejectcontext Company inv:self.employee->reject( isMarried )->isEmpty()

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ForAll OperationForAll Operationcontext Companyinv: 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)

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Exists OperationExists Operation

context Company inv:self.employee->exists( forename = 'Jack' )UML OCL 2.0 Adopted Specification 29

context Company inv:self.employee->exists( p | p.forename = 'Jack' )

context Company inv:self.employee->exists( p : Person | p.forename = 'Jack' )

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Iterate OperationIterate 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))

im ntu software development methods, fall2004 software development methods, fall 2004 ocl -- 1...

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