Jan Pettersen Nytun, UIA, page 1 Content HISTORY COLLECTION - PowerPoint PPT Presentation

Jan Pettersen Nytun, UIA, page 1

Content • HISTORY • COLLECTION TYPES AND QUERING IN OCL • FORMAL LANGUAGE - STATEMENT EXAMPLES • CONSTRAINTS AND OCL • EXAMPLES Jan Pettersen Nytun, UIA, page 2

History • Formal Languages like Z, have for a long time (ca. 1970) been used to describe things in a precise and unambiguous way. • OCL was developed by IBM (1995) and is a part of UML. • It emphasize precision and simplicity . There is no use of special mathematical symbols. Jan Pettersen Nytun, UIA, page 3

Aligning OCL with the OO-Concepts Level Class Property Ass. OCL 2 the class the property association an OCL construct (metamodel) concept concept concept as a concept a specific a specific 1 a specific class OCL Formulas property association an object of a a link between a formula 0 a slot with value class objects instantiated Jan Pettersen Nytun, UIA, page 4

Content • HISTORY • COLLECTION TYPES AND QUERING IN OCL • FORMAL LANGUAGE - STATEMENT EXAMPLES • CONSTRAINTS AND OCL • EXAMPLES Jan Pettersen Nytun, UIA, page 5

Some Collection Types in OCL • A Set is the mathematical set (no duplicate elements). • A Bag is like a set, which may contain duplicates (i.e., the same element may be in a bag twice or more). • A Sequence is like a Bag in which the elements are ordered. Both Bags and Sets have no order defined on them. Jan Pettersen Nytun, UIA, page 6

Self [2]: ”Each OCL expression is written in the context of an instance of a specific type. In an OCL expression the name self is used to refer to the contextual instance.” context Gang inv : self.member… member Gang GangMember 1..* 0..* model When self is A:Gang then instance self.member is: Set{@M1,@M2} :Set(GangMember) (example) self.member self M1:GangMember A:Gang M3:GangMember M2:GangMember B:Gang M4:GangMember M5:GangMember

One More Navigation Example Model alternative Quiz Question AnswerAlternative * * * 1..* contex Quiz inv : incomplete constraint self.question.alternative… self self.question self.question.alternative When the complete constraint is quiz2:Quiz q3:Question a4:AnswerAlternative checked, then self is bound to self self.question self.question.alternative one Quiz object at a time and then the constraint is quiz1:Quiz q1:Question a1:AnswerAlternative checked for that a2:AnswerAlternative bound object. q2:Question a3:AnswerAlternative

The Example continues… Using OCL as a Query Language: Finding all m em bers no m atter which Gang they belong to OCL is case sensitive! Using USE as OCL tool.

Alternative way to find all m em bers no m atter which Gang they belong to Single navigation of an association results in a Set. Combined navigations results in a Bag

Allowing a Mem ber to be Mem ber of Several Gangs belonging to two gangs Jan Pettersen Nytun, UIA, page 12

Allowing a Mem ber to be Mem ber of Several Gangs belonging to two gangs Jan Pettersen Nytun, UIA, page 13

asSet Jan Pettersen Nytun, UIA, page 14

Jan Pettersen Nytun, UIA, page 15

Finding all m em bers of the B-gang

Content • HISTORY • COLLECTION TYPES AND QUERING IN OCL • FORMAL LANGUAGE - STATEMENT EXAMPLES • CONSTRAINTS AND OCL • EXAMPLES Jan Pettersen Nytun, UIA, page 17

Logical im plication – p im plies q p  q If p is true then also q must be true. “p  q” is called a predicate A predicate is a statement that may be true or false depending on the values of its variables.

Universal Quantification: ∀ In predicate logic, universal quantification formalizes the notion that a logical predicate is true for all the values that can be bound to the variable. E.g.: ∀ a ∈ Integer | (a > 10) → (a + 1 > 10) Can be read as: For all a of type Integer the following is true: if a is greater then 10 then a +1 is also greater then 10 Jan Pettersen Nytun, UIA, page 19

Example: Transitivity In logic and mathematics, a binary relation R is transitive if xRy and yRz together imply xRz In predicate logic : ∀ a,b,c ∈ X | a R b ∧ b R c → a R c Less than (<) is a transitive relation: ∀ a,b,c ∈ Integer | a < b ∧ b < c → a < c In english: For all Integer a , b , c the following is true if a < b and b < c then also a < c (e.g., 1<2 ∧ 2<4 → 1<4 ) Is mother of a transitive relation? Jan Pettersen Nytun, UIA, page 20

Content • HISTORY • COLLECTION TYPES AND QUERING IN OCL • FORMAL LANGUAGE - STATEMENT EXAMPLES • CONSTRAINTS AND OCL • EXAMPLES Jan Pettersen Nytun, UIA, page 21

Constraint [1]: … condition or restriction represented as an expression…. can be attached to any UML model element…. indicates a restriction that must be enforced by correct design of the system… Jan Pettersen Nytun, UIA, page 22

Why OCL? • The power of the graphical part of UML is limited! • OCL gives you power to improve the documentation in a precise and unambiguous way. • OCL parsers (/ evaluators) ensure that the constraints are meaningful and well formed within the model. • To do MDD the models have to be unambiguous (e.g., when doing code generation, transformations). Jan Pettersen Nytun, UIA, page 23

Where To Use OCL?  Invariants on classes and types  Precondition and postconditions on operations (methods)  Constraints on operations: operation=expression (the return value)  … Jan Pettersen Nytun, UIA, page 24

Content • HISTORY • COLLECTION TYPES AND QUERING IN OCL • FORMAL LANGUAGE - STATEMENT EXAMPLES • CONSTRAINTS AND OCL • EXAMPLES Jan Pettersen Nytun, UIA, page 25

An Invariant Example: Use of Size An invariant is predicate that is always true (i.e., when the system is at “rest”.) Gang name : String +member GangMember isArmy : Boolean 1..* 1..* 0..* 0..* register(newMember : GangMember) -- The gang is an army if there are more than 100 members. context Gang inv oneSimpleConstraint : self. isArmy = ( member ->size() > 100 ) Jan Pettersen Nytun, UIA, page 26

Use of pre –and post-condition Gang name : String GangMember +member isArmy : Boolean 1..* 1..* 0..* register(newMember : GangMember) -- The gang has grown with one when a new member has been added. -- NB! @pre accesses the value before executing the operation context Gang :: register(newMember : GangMember) pre: not member ->includes( newMember ) post : member = member @pre->including( newMember ) Jan Pettersen Nytun, UIA, page 27

Com m ents to Previous Slide collection-> includes (object: T): Boolean is True if object is an element of collection . E.g.: Set{@m 1,@m 2}->includes(@m 2) = true p@pre refers to the value of p before the operation was executed. E.g.: member @pre is the set member before the operation was executed. collection-> including (object: T): Bag(T) is the bag with all elements of collection plus object . E.g.: Set{@m 1,@m 2}->including(@m 3) = Set{@m 1,@m 2,@m 3}. Jan Pettersen Nytun, UIA, page 28

Using OCL in USE What we want: An account has either a person as owner or a cooperation as owner context Account inv : personOwner->size() = 1 implies cooperationOwner->size() = 0

What is this? This should not be allowed – this is not xor!

Modify the Constraint: context Account inv: (personOwner-> size() = 1 implies cooperationOwner-> size() = 0) and (personOwner-> size() = 0 implies cooperationOwner-> size() = 1)

forAll Variations (math. notation: ∀ ) employee Person Company * * age : Integer context Company inv : self.employee->forAll( age <= 70 ) context Company inv : self.employee->forAll( p | p.age <= 70 ) Equivalent Constraints context Company inv : self.employee->forAll( p : Person | p.age <= 70 ) Jan Pettersen Nytun, UIA, page 34

Example: exis xists (math. notation: ∃ ) collection  exists(exp : OclExpression) : Boolean True if exp is true for one elements of the collection Car +owner Gun +owner Person type : String 0..* 0..* 1 1 1 1 0..* 0..* age : Integer Gang +member GangMember name : String 1..* 1..* 1 1 isArmy : Boolean -- Every Gang must have a member with a car contex Gang inv: member->exists(car->size()>0) Jan Pettersen Nytun, UIA, page 35