Object Constraint Language

in Together

Dan Massey

Y&L Consulting

Picking up From Logicians

Follows 3242 presentation to go in depth on OCL and using OCL in tools

The preconference tutorial used the slides from session 3242 as the first third of the presentation.

OCL TopicsOCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

OCL TopicsOCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

OCL isStrongly typed declarative language

Small set of built-in types, including collections

User-defined types and operators

OCL Basic TypesBoolean true or falseInteger theoretically unlimited natural

numbers, subtype of RealReal mathematical Real, no specific

implementation impliedString ‘sequence of characters’

Boolean Operationsa : Boolean b : Boolean

a and b a or b a xor bnot a a = b a <> ba implies b

implies constraint:if a is true then b must be true

Numeric OperatorsComparison= equals <> not equals< less > more<= less or equal >= more or equal

Math+ addition - subtraction* multiplication / division

Every Type in OCL is an Object

a : Integer b:Integer

a.mod(b) a.div(b)a.abs() a.max(b)a.min(b) a.round()a.floor()

Operators are just infix notation operations.

String Operationsa : String b : String

a = b a <> ba.concat(b) a.size()a.toLower() a.toUpper()a.subString(1, 3)

Operations return new Strings.

OCL ConditionalOCL provides one conditional construct:

if <Boolean expression>then <expression>else <expression>endif

No “elseif” or “switch”/“case”

OCL Operation PrecedenceGrouping ()Path resolution ::Message notation . -> also ^ ^^Unary - notMultiplication/Division * /Addition/Subtraction + -Comparison < > <= >= <> =Logical and or xorLogical implication implies

User-Defined TypesClasses, Interfaces, etc. defined in the model

Users may overload infix and unary operators:Multiply Money by a RealAdd two Distance values

OCL CollectionsRefreshing our memories, we have:CollectionBag SequenceSet OrderedSet

OCL allows you to treat any instance like a collection. You can ask if a single attribute is empty.

Collections must by Typed

Set(Bid)Bag(String)

Like generics in Java or templates in C++.

Collections LiteralsUse curly brackets around comma lists to specify

Collection literals.

Bag {‘sock’, ‘sock’, ‘shirt’, ‘sweater’, ‘sock’}Sequence {‘abe’, ‘bob’, ‘bob’, ‘tim’, ‘zak’}Set {16.0, 2.0, 64.0, 8.0, 128.0, 3.5}OrderedSet {1, 2, 4, 8, 16, 32, 64, 128}

You can also specify Collections of Collections.

Basic Collections Operations

a : Set(String) b : String c : Set(String)

a = c a <> c

a->size() a->count(b)

a->excludes(b) a->excludesAll(c)a->includes(b) a->includesAll(c)a->isEmpty() a->notEmpty()a->sum() -- contents are of type supporting +

More Collections Operations

OCL supports a wide range of Collection operations that vary by Collection type.

first(), last(), at(i : Integer), etc. for {ordered} collections

union(), -, asSet(), including(), symmetricDifference(collection : Collection) are a sample

FlattenRecursively adds the members of nested

collections to a single collection.

context MyTypedef: a : Set(Set(Integer)) =

Set {Set{1, 2, 3}, Set{3, 4, 5}, Set{4, 5, 6}}

a->flatten() = Set{2, 3, 1, 5, 4, 6} -- no order

Collection LoopsOCL supports an iterate() operation for

Collections. On top of that idea, OCL provides a set of Collection operations that accept expression.

Examples:any(expression) exists(expression)collect(expression) one(expression)select(expression) reject(expression)

Other OCL TypesOclAny the root TypeOclVoidthe “null” Type “undefined”OclType a type, like “Class” in JavaOCL provides operations for type identification.

Tuple group of named valuesTuple {name : String = ‘Dan’,

role : Role = Role::Speaker}

OCL TopicsOCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

Liquid Lemons Domain

LL Invariantscontext Sale-- a Sale has one or more itemsinv numberOfSaleItems : items->size() > 1

-- a Sale's subtotal may not be less than zeroinv subtotalGreaterThanZero : subtotal().amount >

0.0 and subtotal().currency = Currency::USDollars

LL Pre and Postcontext LiquidLemons::addLemonade(flavor :

Flavor, size : DrinkSize)pre activeSale : currentSale->size() = 1pre mustHaveFlavor : not flavor.oclIsUndefined()pre mustSpecifySize : not size.oclIsUndefined()post newLemonade :

currentLemonade->size() = 1

LL Query

Collections Queriescontext ItemAnalyzer::averagePrice() : Moneybody: items.basePrice()->sum() /

items.basePrice()->size()

context ItemAnalyzer::uniqueModDescriptions() : Set(String)

body: items.modDescriptions() ->flatten()->asSet()

Composite QueriesUse small methods with single responsibilities to build up

larger functions.

-- the total we want is subtotal plus taxcontext Sale::total() : Moneybody: subtotal() + tax()

-- tax is the subtotal times the local tax ratecontext Sale::tax() : Moneybody: subtotal() * Tax::localRate

Composite Queries Cont.context Sale::subtotal() : Moneybody: items.price()->sum()

context LineItem::price() : Moneybody: basePrice() + modsPrice()

context LineItem::modsPrice() : Moneybody: modifiers.price()->sum()

Don’t Do Thiscontext LineItem::basePrice() : Moneybody: if size = DrinkSize::Small then if flavor = Flavor::Regular then Money::newInstance(1.23, Currency::USDollars) else Money::newInstance(1.73, Currency::USDollars) endif else if flavor = Flavor::Regular then Money::newInstance(2.43, Currency::USDollars) else Money::newInstance(3.13, Currency::USDollars) endif endif

Use PolymorphismLittle policy classes are an extension of the little operations

idea. Smaller rules are easier to read.

context LargeRegularLemonade::basePrice() : Moneybody: Money::newInstance(2.43, Currency::USDollars)

context SmallFlavoredLemonade::basePrice() : Moneybody: Money::newInstance(1.72, Currency::USDollars)

OCL TopicsOCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

Where Does the OCL Go?

Use the named property fields and boxes.Shows up in generated docs and XMI export.Not visible in diagrams.

OCL Notes

Attach notes containing OCL to correct contexts.OCL is visible in the diagrams.Potential to clutter the model.

Together Designer

Syntax checked OCL in “Constraint Notes” that establish context.

Now in field test.

OCL TopicsOCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

Domain OptionsTic-Tac-ToeAntsElectronic VotingPoemGolfTurtle LogoDog Kennel