Object Constraint Language

1
Object Constraint Language

• in Together
• Dan Massey
• YL 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

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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 ltgt b
• a implies b
• implies constraint
• if a is true then b must be true

8
Numeric Operators

• Comparison
• equals ltgt not equals
• lt less gt more
• lt less or equal gt more or equal
• Math
• addition - subtraction
• multiplication / division

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Every Type in OCL is an Object

• a Integer bInteger
• a.mod(b) a.div(b)
• a.abs() a.max(b)
• a.min(b) a.round()
• a.floor()
• Operators are just infix notation operations.

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String Operations

• a String b String
• a b a ltgt b
• a.concat(b) a.size()
• a.toLower() a.toUpper()
• a.subString(1, 3)
• Operations return new Strings.

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OCL Conditional

• OCL provides one conditional construct
• if ltBoolean expressiongt
• then ltexpressiongt
• else ltexpressiongt
• endif
• No elseif or switch/case

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OCL Operation Precedence

• Grouping ()
• Path resolution
• Message notation . -gt also
• Unary - not
• Multiplication/Division /
• Addition/Subtraction -
• Comparison lt gt lt gt ltgt
• Logical and or xor
• Logical implication implies

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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

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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.

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Collections must by Typed

• Set(Bid)
• Bag(String)
• Like generics in Java or templates in C.

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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.

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Basic Collections Operations

• a Set(String) b String c Set(String)
• a c a ltgt c
• a-gtsize() a-gtcount(b)
• a-gtexcludes(b) a-gtexcludesAll(c)
• a-gtincludes(b) a-gtincludesAll(c)
• a-gtisEmpty() a-gtnotEmpty()
• a-gtsum() -- contents are of type supporting

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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

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Flatten

• Recursively adds the members of nested
  collections to a single collection.
• context MyType
• def a Set(Set(Integer)) Set Set1, 2, 3,
  Set3, 4, 5, Set4, 5, 6
• a-gtflatten() Set2, 3, 1, 5, 4, 6 -- no order

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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)

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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
  RoleSpeaker

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OCL Topics

• OCL Basics
• The LiquidLemons Example
• OCL in Together
• Team Modeling Exercise

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Liquid Lemons Domain
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LL Invariants

• context Sale
• -- a Sale has zero or more items
• inv numberOfSaleItems not items-gtsize() gt 0
• -- a Sale's subtotal may not be less than zero
• inv subtotalGreaterThanZero subtotal().amount gt
  0.0 and subtotal().currency CurrencyUSDollars

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LL Pre and Post

• context LiquidLemonsaddLemonade(flavor
  Flavor, size DrinkSize)
• pre activeSale currentSale-gtsize() 1
• pre mustHaveFlavor not flavor.oclIsUndefined()
• pre mustSpecifySize not size.oclIsUndefined()
• post newLemonade currentLemonade-gtsize() 1

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LL Query
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Collections Queries

• context ItemAnalyzeraveragePrice() Money
• body items.basePrice()-gtsum() /
  items.basePrice()-gtsize()
• context ItemAnalyzeruniqueModDescriptions()
  Set(String)
• body items.modDescriptions()-gtflatten()-gtasSet()

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Composite Queries

• Use small methods with single responsibilities to
  build up larger functions.
• -- the total we want is subtotal plus tax
• context Saletotal() Money
• body subtotal() tax()
• -- tax is the subtotal times the local tax rate
• context Saletax() Money
• body subtotal() TaxlocalRate

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Composite Queries Cont.

• context Salesubtotal() Money
• body items.price()-gtsum()
• context LineItemprice() Money
• body basePrice() modsPrice()
• context LineItemmodsPrice() Money
• body modifiers.price()-gtsum()

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Dont Do This

• context LineItembasePrice() Money
• body
• if size DrinkSizeSmall then
• if flavor FlavorRegular then
• MoneynewInstance(1.23, CurrencyUSDollars)
• else
• MoneynewInstance(1.73, CurrencyUSDollars
  )
• endif
• else
• if flavor FlavorRegular then
• MoneynewInstance(2.43, CurrencyUSDollars
  )
• else
• MoneynewInstance(3.13, CurrencyUSDollars
  )
• endif
• endif

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Use Polymorphism

• Little policy classes are an extension of the
  little operations idea. Smaller rules are easier
  to read.
• context LargeRegularLemonadebasePrice() Money
• body MoneynewInstance(2.43, CurrencyUSDollars
  )
• context SmallFlavoredLemonadebasePrice()
  Money
• body MoneynewInstance(1.72, CurrencyUSDollars
  )

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OCL Topics

• OCL Basics
• The LiquidLemons Example
• OCL in Together
• Team Modeling Exercise

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Where Does the OCL Go?

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

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OCL Notes

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

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Together Designer

• Syntax checked OCL in Constraint Notes that
  establish context.
• Now in field test.

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OCL Topics

• OCL Basics
• The LiquidLemons Example
• OCL in Together
• Team Modeling Exercise

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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.
• Were 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

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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.