SoftwareEngineering (OCL) LinaYE SoftwareEngineering(OCL)linaye/OCL_GL.pdf · SoftwareEngineering...

Software Engineering(OCL)

Lina YE

Introduction

ConstraintsContext and Self

Invariant

Pre- and Post-condition

Constraints on Attributes

LanguageAccess to characteristics

Types

Variable

Collections

OCL function

Example

Software Engineering (OCL)Object Constraint Language

Lina YE

https://www.lri.fr/~linaye/GL.html

[email protected] 3, 2017-2018

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Software Engineering (OCL) Forward

https://www.lri.fr/~linaye/GL.html


Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Plan1 Introduction2 Constraints

Context and SelfInvariantPre- and Post-conditionConstraints on Attributes

3 LanguageAccess to characteristicsTypesVariableCollectionsOCL function

4 Example

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Software Engineering (OCL) ForwardBack


Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

MotivationWhy OCL

Cannot represent all the relevant aspects of aspecification (e.g., class diagram)

Need to describe additional constraints withoutambiguities

Formal languages requires a strong mathematicalbackground

What is OCLFormal language to express constraints, that remainseasy to read and write

Developed by IBM and standardized by OMG

Integrated into the UML standard

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Lina YE

Introduction


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Types

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Collections

OCL function

Example

Objet Constraint Language

Where to useSpecify invariants on classes and types in the class model

Describe pre- and post-conditions on operations andmethods

Describe guards

As a navigation language

etc.

ExampleHow to represent the constraint that the age of anemployee cannot be smaller than 18?

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Lina YE

Introduction


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Types

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Collections

OCL function

Example

Objet Constraint Language

Pure specification language: do not have side effetevaluation of an OCL expression returns a valuethis evaluation do not alter the system state and isinstantaneous

Not a programming languagecannot write program logic in OCLcannot invoke processes or activate non-queryoperations

Typed language: each expression has a typeexpression must obey the type conformance rules ofOCLeach classifier defined in a UML model represents adistinct OCL typeincludes a set of supplementary predefined types

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Context

Each constraint must be associated to one model element

Such an element constitutes the context of the constraint

Syntax: keyword context

exampleclass: nameClasscontext Person

operation: nameClass::nameOperation(param1:Type1,...):TypeReturnedcontext Account::getSolde(): Real

attribute: nameClass::nameAtt: TypeAttcontext Person::age : Integer

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Lina YE

Introduction


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Types

Variable

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OCL function

Example

Self

In an OCL expression, reserved word self is used torefer to the contextual instance

If the context is Person, then self refers to an instance ofPerson

This keyword can be omitted when the context is clear

examplecontext Personself.name

context Personname

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

InvariantDetermine a constraint that should be always true for allinstances of a typeSyntaxinv: <logic expression>

exampleValue of attribute nbEmployees in instances of Companymust be less than or equal to 50context Companyinv: self.nbEmployees≤50

The stock price of each company is greater than 0(stockPrice() is a operation defined in the classCompany)context Companyinv: self.stockPrice()>0

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Pre-condition

Constraints associated with an operation or otherbehavioral feature

Constraint assumed to be true before the execution ofthe operation

Syntaxpre: <logic expression>

exampleThe age of a person who has an income must be olderthan or equal to 18 (income() is an operation defined inthe class Person)context Person:: income(): Integerpre: self.age≥18

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Post-conditionConstraints associated with an operation or otherbehavioral featureConstraint satisfied after the execution of the operationKeyword result denotes the value returned by theoperation, whose type is the returned typeKeyword @pre denotes the attribute value before theoperationSyntaxpost: <logic expression>

exampleThe age of a person who has an income cannot besmaller than 18, and the income must be less than 5000context Person:: income(): Integerpre: self.age≥18post: result<5000

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Init

Reserved word init is used to represent the initial value

Possibility to precise the initial value of an attribute or anassociation end when the object is created

Syntaxinit: expression

exampleAttribute isMarried in Person is initialized to falsecontext Person:: isMarried: Booleaninit: false

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Derive

Reserved word derive is used to represent the derivedvalue

Precise how to obtain the derived value of an attributebased on the value of other attributes, such a constraintshould always be respected

Syntaxderive: expression

exampleThe age of one person is obtained by subtracting theirbirth date from the current datecontext Person:: age: Integerderive: currentDate-dateOfBirth

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Access to characteristics of anobject

The access of attributes and operations of an object isspecified by a dot followed by their name

Syntaxself.nameAttributeself.nameOperation(arg1, ..., argn )

examplecontext Personself.ageself.income()

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Lina YE

Introduction


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Types

Variable

Collections

OCL function

Example

Navigation

From an object, an association is navigated by a dotfollowed by the opposite role name

Value of expression depends on maximal multiplicity ofthe association end1: value is an object (”.“) or can also be used as a setcontaining a single object (”→“)∗: value is a set of objects (”→“)

For optional associations, it is useful to check whetherthere is an object or not when navigating the association

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Navigation: example

Example

context Companyinv: self.manager.isUnemployed=falseinv: self.employee→notEmpty()

self.manager is an object of type Personcontext Companyinv: self.manager.age> 40

self.manager as a setcontext Companyinv: self.manager→ size()=1

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Navigation: example

Example

context Companyinv: self.manager.isUnemployed=falseinv: self.employee→notEmpty()self.manager is an object of type Personcontext Companyinv: self.manager.age> 40

self.manager as a setcontext Companyinv: self.manager→ size()=1

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Enumeration: example

Example

context Personinv: self.wife→notEmpty() impliesself.gender=Gender::Male andself.husband→ notEmpty() impliesself.gender=Gender::Female

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

List of TypesPredefined types with their operators

Types OperatorsBoolean and; or; xor; not; implies; if-then-else-endif;...Integer ∗; +;−; /; abs(); ...Real ∗; +;−; /; abs(); floor (); ...String concat(s: String); size(); substring(lower: Integer, upper: Integer);...

ImpliesP1 P2 P1 implies P2True True TrueTrue False FalseFalse True TrueFalse False True

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Operations on Types

One person who is married must be more than 18 yearsold

One person is either male or female but cannot be both

context Personinv: self.isMarried implies self.age>18

context Personinv: self.gender=Gender::male xorself.gender=Gender::female

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Create a Variable

If the same expression is used more than one time

For the better readability of the constraint

SyntaxWith keywords let...inlet < variable >: TypeVar=< request > in< expression >

With keyword defdef: < variable >: TypeVar=< request >< expression >

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Create a Variableexample

An unemployed person has no job. Otherwise, he has atleast one job.

The name of one person is the concatenation of firstname and last name

context Personinv: let numberJobs: Integer=self.job→size() inif isUnemployed then numberJobs=0else numberJobs > 0endif

context Persondef: name: String=self.firstName.concat(’ ’).concat(lastName)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Collection

Conversion of an association to a type within OCL

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Operation on CollectionSyntax

For a collection,→ is used to apply some operation on it:nameCollection→ operation()Recall: the dot is used for the access of a property of anobject

Some examplessize(): Integer (return the number of elements in thecollection)

includes(object: T): Boolean (return true if object isincluded in the collection)

excludes(object: T): Boolean (return true if object is notin the collection)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Operation on Collection

Some examplescount(object: T): Integer (return the number of object)

isEmpty(): Boolean (return true if the collection is empty)

notEmpty(): Boolean (return true if the collection is notempty)

includesAll(c: Collection(T)): Boolean (return true if thecollection contains all elements of c)

excludesAll(c: Collection(T)): Boolean (return true if thecollection does not contains any element of c)

sum(): T (return the sum of all elements in the collection)

union(set: Set(T)): Set(T) (return the union of self withset)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example


Some examplesany(exp: OclExpression): Type (return any element inself validating exp)

=(set: Set(T)): Boolean (return true if self and setcontain exactly the same elements)

including(object: T): Set(T) (return a collection thatcontains all elements of self plus object)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example


One company has at least one employee

The manager of a company is also an employee

context Companyinv: self.employee→ size() > 0inv: self.employee→ notEmpty()

context Companyinv: self.employee→ includes(self.manager)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example


One company has at least one employee

The manager of a company is also an employee

context Companyinv: self.employee→ size() > 0inv: self.employee→ notEmpty()context Companyinv: self.employee→ includes(self.manager)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Operation on Elements

Syntaxcollection→ operation (expression)collection→ operation (v | expression-with-v)collection→ operation (v: Type | expression-with-v)

The expression is applied on each element of the collection

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Operation on Elementsselect: generate a sub-collection that contains only theelements satisfying expression

reject: generate a sub-collection that contains only theelements that does not satisfy expression

Each company must have at least one employee that is morethan 50 years old

context Company:inv: self.employee→ select(p: Person | p.age> 50)→notEmpty()

context Company:inv: self.employee→ reject(p: Person | p.age<= 50)→ notEmpty()

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example


forAll: return true if the expression is true for eachelement

exists: return true if the expression is true for at leastone element

Each company must have at least one employee that is morethan 50 years old

context Company:inv: self.employee→ not (forAll(p: Person |p.age<= 50))

context Company:inv: self.employee→ exists(p: Person | p.age> 50)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example


The employer of an employee that participates a team projectis the organisation that possesses this project

context Person:inv: (self.employer→size()=1 and self.team→size()=1)implies self.employer=self.team.project.organisation

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example


collect: create a new collection, for which each elementis the result of the expression

It is required to obtain the set of birthday dates for allemployees

context Companyself.employee→ collect (p: Person | p.birthdayDate)

Shorthand for collect

context Companyself.employee.birthdayDate

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Iterate Operation

iterate: calculate an accumulator whose value is built upduring the iteration of the collection.

Collection→ iterate (e: Type; acc: Type=initialexpression | expression with e and acc)

The sum of ages of all children for a person

context Personself.children→ iterate (p: Person; acc: Integer=0 |acc=acc+p.age)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Re-typing or Casting

With o.oclAsType(T2), one re-types an object o of typeT1 into another type T2

Let type Super be a super type of type Sub

Allows one to use a property of an object defined on asubtype of the currently known type of the objectcontext Superinv: self.oclAsType(Sub).p (accesses the p propertydefined in Sub, valid when actual type of self is Sub,otherwise, invalid)

Can be used to access a property of a superclasscontext Subinv: self.oclAsType(Super).p (accesses the p propertydefined in Super)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Other functions

oclIsTypeOf(t: Type): return true if the type of self and tare the same

oclIsKindOf(t: Type): return true if t is a direct/indirect(supertype) type of self

oclIsNew: used in a post-condition, return true if theobject has been created during the operation

Examplecontext Personinv: self.oclIsTypeOf(Person) –trueinv: self.oclIsTypeOf(Company) –false

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Class features

Features of a class, not of its instances

Either predefined or user-defined

Predefined: allInstances holds on all types and returnsthe set of class instances

There are at most 100 personscontext Personinv: Person.allInstances()→ size() ≤ 100A user-defined feature averageAge of class Personcontext PersonPerson.averageAge=(Person.allInstances()→ collect(age)→ sum()) / (Person.allInstances()→ size())

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Example 1

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

OCL for example 1

A hotel never has a floor 13, because of superstition.

context Roominv: self.floor <> 13

context BathRoominv: self.floor <> 13

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

OCL for example 1

The number of clients for each room must be smaller or equalto the number of beds in the rented room. The children under4 are not ”taken into account“ in this calculation rule (condition: maximum of one child under 4 per room).

context Roominv: clients→size()≤nbBeds or(clients→ size()=nbBeds+1 and clients→exists(p:Person| p.age<4))

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

OCL for example 1

Each floor owns at least one room except for floor 13.

context Hotelinv: Sequence{floorMin, ..., floorMax}→forAll (f:Integer | f<>13 implies self.room→ select(r:Room|r.floor=f)→ notEmpty())

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

OCL for example 1

Rooms are on the first to the last floor.

context Hotelinv: self.room→ forAll(r: Room | r.floor≤ self.floorMaxand r.floor≥ self.floorMin)

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

OCL for example 1

A room can be repainted when it is not occupied. Oncerepainted, the cost of a room is 10% more.

context Room::repaint(c: Color)pre: clients→ isEmpty()post: price=price@pre*1.1

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

OCL for example 1

The hotel income is equal to the sum of prices for all rentedrooms.

context Hotel::income():Realpost: result=self.room→ select(r: Room | r.clients→notEmpty())→ collect(r:Room | r.price)→ sum()

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

Example 2

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

OCL for example 2

The salary of an employee cannot be greater than thesalary of his/her supervisercontext Employeeinv: self.supervisor→ notEmpty() impliesself.salary < self.supervisor.salary

The condition notEmpty must be tested since themultiplicity of the role is not mandatory

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Lina YE

Introduction


Invariant




Types

Variable

Collections

OCL function

Example

OCL for example 2

The SSN of employees is an identifier (or a key)context Employeeinv: Employee.allInstances()→forAll(e1, e2 | e1 <> e2implies e1.SSN <> e2.SSN)

The name and relationship of dependents is a partialidentifier: they are unique among all dependents of anemployeecontext Employeeinv: self.dependents→ notEmpty() impliesself.dependents→ forAll(e1, e2 | e1 <> e2 impliese1.name <> e2.name or e1.relationship <>e2.relationship)

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Lina YE

Introduction


Invariant




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Variable

Collections

OCL function

Example

OCL for example 2

An employee cannot supervise him/herselfcontext Employeeinv: self.subordinates→excludes(self)

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