Object Constraint Language

1. Object Constraint Language in Together Dan Massey Y&L Consulting

2. 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.

3. OCL Topics • OCL Basics • The LiquidLemons Example • OCL in Together • Team Modeling Exercise

4. OCL Topics • OCL Basics • The LiquidLemons Example • OCL in Together • Team Modeling Exercise

5. OCL is • Strongly typed declarative language • Small set of built-in types, including collections • User-defined types and operators

6. OCL Basic Types • Boolean true or false • Integer theoretically unlimited natural numbers, subtype of Real • Real mathematical Real, no specific • implementation implied • String ‘sequence of characters’

7. Boolean Operations • a : Boolean b : Boolean • a and b a or b a xor b • not a a = b a <> b • a implies b • implies constraint: • if a is true then b must be true

8. Numeric Operators • Comparison • = equals <> not equals • < less > more • <= less or equal >= more or equal • Math • + addition - subtraction • * multiplication / division

9. 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.

10. String Operations • a : String b : String • a = b a <> b • a.concat(b) a.size() • a.toLower() a.toUpper() • a.subString(1, 3) • Operations return new Strings.

11. OCL Conditional • OCL provides one conditional construct: • if <Boolean expression> • then <expression> • else <expression> • endif • No “elseif” or “switch”/“case”

12. OCL Operation Precedence • Grouping () • Path resolution :: • Message notation . -> also ^ ^^ • Unary - not • Multiplication/Division * / • Addition/Subtraction + - • Comparison < > <= >= <> = • Logical and or xor • Logical implication implies

13. User-Defined Types • Classes, Interfaces, etc. defined in the model • Users may overload infix and unary operators: • Multiply Money by a Real • Add two Distance values

14. OCL Collections • Refreshing our memories, we have: • Collection • Bag Sequence • Set OrderedSet • OCL allows you to treat any instance like a collection. You can ask if a single attributed is empty.

15. Collections must by Typed • Set(Bid) • Bag(String) • Like generics in Java or templates in C++.

16. Collections Literals • Use 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.

17. 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 +

18. 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

19. Flatten • Recursively adds the members of nested collections to a single collection. • contextMyType • def: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

20. Collection Loops • OCL 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)

21. Other OCL Types • OclAny the root Type • OclVoid the “null” Type “undefined” • OclType a type, like “Class” in Java • OCL provides operations for type identification. • Tuple group of named values • Tuple {name : String = ‘Dan’, role : Role = Role::Speaker}

22. OCL Topics • OCL Basics • The LiquidLemons Example • OCL in Together • Team Modeling Exercise

23. Liquid Lemons Domain

24. LL Invariants • contextSale • -- a Sale has zero or more items • invnumberOfSaleItems:notitems->size()>=0 • -- a Sale's subtotal may not be less than zero • invsubtotalGreaterThanZero:subtotal().amount>0.0andsubtotal().currency= Currency::USDollars

25. LL Pre and Post • contextLiquidLemons::addLemonade(flavor:Flavor,size:DrinkSize) • preactiveSale:currentSale->size()=1 • premustHaveFlavor:notflavor.oclIsUndefined() • premustSpecifySize:notsize.oclIsUndefined() • postnewLemonade:currentLemonade->size()=1

26. LL Query

27. Collections Queries • contextItemAnalyzer::averagePrice():Money • body:items.basePrice()->sum()/items.basePrice()->size() • contextItemAnalyzer::uniqueModDescriptions():Set(String) • body:items.modDescriptions()->flatten()->asSet()

28. Composite Queries • Use small methods with single responsibilities to build up larger functions. • -- the total we want is subtotal plus tax • contextSale::total():Money • body:subtotal()+tax() • -- tax is the subtotal times the local tax rate • contextSale::tax():Money • body:subtotal()*Tax::localRate

29. Composite Queries Cont. • contextSale::subtotal():Money • body:items.price()->sum() • contextLineItem::price():Money • body:basePrice()+modsPrice() • contextLineItem::modsPrice():Money • body:modifiers.price()->sum()

30. Don’t Do This • contextLineItem::basePrice():Money • body: • ifsize=DrinkSize::Smallthen • ifflavor=Flavor::Regularthen • Money::newInstance(1.23,Currency::USDollars) • else • Money::newInstance(1.73,Currency::USDollars) • endif • else • ifflavor=Flavor::Regularthen • Money::newInstance(2.43,Currency::USDollars) • else • Money::newInstance(3.13,Currency::USDollars) • endif • endif

31. Use Polymorphism • Little policy classes are an extension of the little operations idea. Smaller rules are easier to read. • contextLargeRegularLemonade::basePrice():Money • body:Money::newInstance(2.43,Currency::USDollars) • contextSmallFlavoredLemonade::basePrice():Money • body:Money::newInstance(1.72,Currency::USDollars)

32. OCL Topics • OCL Basics • The LiquidLemons Example • OCL in Together • Team Modeling Exercise

33. Where Does the OCL Go? • Use the named property fields and boxes. • Shows up in generated docs and XMI export. • Not visible in diagrams.

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

35. Together Designer • Syntax checked OCL in “Constraint Notes” that establish context. • Now in field test.

36. OCL Topics • OCL Basics • The LiquidLemons Example • OCL in Together • Team Modeling Exercise

37. Workshop Model(s) • Scott Ambler addresses writes about model-storming in the October 4th issue of “Software Development” • Short burst of modeling as a team. • We’re model-storming “to analyze requirements”

38. Domain Options • Tic-Tac-Toe • Ants • Electronic Voting • Poem • Golf • Turtle Logo • Dog Kennel

39. Regroup • OCL Benefits • OCL Challenges • Domain Modeling

40. Questions and Answers • See the paper for session 3016 to read more about the LiquidLemons example. The paper also contains a diagram and OCL frojm the Tic-Tac-Toe group modeling activity from the tutorial.