UML Artifacts (Part 2)

1. UML Artifacts (Part 2) Contents • Collaboration Diagrams • State Transition Diagrams • Visibility • Review

2. Collaboration Diagrams For each system operation identified in the Sequence Diagrams, and described in a contract Design a system of interacting objects to perform the operation. The collaboration diagram will indicate the objects participating in the collaboration, and The sequence of messages {message(parameters), sender, receiver} exchanged to achieve the task involved.

3. Actor System System Op SystemOp :ClassA Operation:xxx Precondition:.. 1: message1() :ClassB System Sequence Diagram Contract Collaboration Diagram Collaboration Diagrams +

4. John:Student Student :Student Collaboration Diagrams Notation class instance named instance The Collaboration diagram should consist of illustrations of the messages sent to objects of the classes identified in the creates/destroys, reads, changes sections of the contract. The system operation will be directed to one of the objects in this group that will act as the controller for executing this task.

5. sysOp() optional 1: tot := total():integer :Sale :POST Collaboration Diagrams Illustrating links UML standard syntax for messages return := message(parameter : parameterType) : returnType sender receiver

6. SystemOp( ) CS478:ClassList :Grader Sequence number followed by a * indicates iteration Iteration clause is optional Collaboration Diagrams Illustrating Iteration 1*: [i:=0..19] str : getName(): String receiver sender

7. 1: message( ) :ClassA Collaboration Diagrams Illustrating Iteration In the example described on the previous slide, we assumed that the target object contained a sequence of names (simple strings) as an attribute. More generally the ClassList may be considered a collection of StudentRec objects, and messages may be directed to the collection. The depiction of a message to a multiobject – a group of objects stored in a collection – is indicated on the next slide. Representation of a collection (multiobject)

8. 1: inx := find(name: String): integer v: vector 1: inx := find(name: String): integer :StudentRecord Collaboration Diagrams Given: A vector of StudentRecord Version 1 – message to a collection (but vector is NOT a concept in the problem domain) Version 2 – (preferred) Emphasizes the objects in the collection, not (the solution domain) container.

9. :ClassB :ClassA guard – if true send msg :ClassD :ClassC Collaboration Diagrams Conditional Paths – mutually exclusive messages msg1( ) 1a: [test] msg2( ) 1b: [not test] msg4( ) 1a.1: msg3( ) 1b.1: msg5( )

10. New m:MenuItem 1: create( ) c: Controller 2: add(m) :MenuItem Collaboration Diagrams Creating a new instance during implementation of the system operation Create a new MenuItem, m, and add it to the Menu

11. Refining the Class Diagram • For every class, examine each collaboration diagram and identify • Every message received by an instance of that class – (these will be the methods for that class) • Each object (class) to which an instance of this class sends a message – (these may require reference attributes within the class, depending upon the visibility)

12. Classes to which messages are sent Messages received Refining the Class Diagram Class name Data attributes Link attributes methods Class Description

13. State Transition Diagrams State transition diagrams are a useful tool for constructing the individual classes. Specifically, they aid in two important ways in “fleshing out” the structure of the class: • method development -- State transition diagrams provide the “blueprints” for developing the algorithms that implement methods in the class • attribute identification – Attributes contain the state information needed for regulating the behaviors of the instances of the class When constructing state transition diagrams, take care to ensure that the post-conditions stipulated in the contracts are enforced.

14. Transitions are labeled with the triggering event and the output if any Some events do not trigger a change in state State 2 State 1 States are represented with an oval and label State transitions are represented with a directed arc or line State Transition Diagrams Notation event|output start final state

15. event|output State State Guard condition – transition occurs only if condition is true State Transition Diagrams Additional Notation [boolean condition]

16. off hook|dial tone [valid subscriber] idle talking on hook playing dial tone do: hang up answered digit complete|ringing dialing connecting digit State Transition Diagrams Example – Nested States in Telephone Call active The state labeled active has substates

17. arrival arrival Size0 Size1 size2 departure departure arrival | balk State Transition Diagrams Second Example – A Queue of Capacity Two The queue has three states that indicate its number of occupants. When the queue is full, new arrivals cannot enter, and must leave the system.

18. State State transitions Description of Class Queue class Queue { private: int capacity, size; public: Queue(int cap); void enqueue(Object obj); //precondition: queue not full //post condition: if (queue not full) // size = size + 1 // else no change Object dequeue(); //precondition: queue not empty //post-condition: size = size-1 }

19. Visibility For an object A to send a message to object B, B must be visible to A. In determining the visibility of one object to another, we must decide during the design whether the link between objects A and B is: permanent or transient exclusive or shared fixed or variable

20. Clock Counter * modulus count 3 Visibility Example 1. permanent, exclusive , and fixed Consider a clock composed of three Counters (hours, mins, secs) • The Counters have the same lifetime as the Clock – They are created with the clock and dissolved when the clock is out of scope. • The Counters are bound exclusively to the Clock – They cannot be referenced by any other object in the system

21. Visibility Implementation of the association between Clock and Counters class Clock { private: Counter hours, mins, secs; public: Counter( ) : hours(24), mins(60), secs(60) {}; //other methods } C++ header file

22. Computer ProductSpec * describes Visibility Example 2. permanent, shared, fixed The ProductSpec exists before an instance of the product is created. That product (computer) will have a permanent association with its ProductSpec that it will share access to with other computers of the same model.

23. The reference variable ps must be initialized in an initialization list, and cannot be reassigned during the life of the object. Visibility (Partial) Specification of class Computer class Computer { private: ProductSpec & ps; public: Computer (ProductSpec & theMod) : ps(theMod) {}; //other methods }

24. permanent and exclusive; lifetime of the counter is bounded by the lifetime of the object itself. Can be non-permanent, variable, and shared Permanent and fixed, but not necessarily exclusive; lifetime of the ProductSpec will exceed that of object Visibility Attribute visibility -- an association that must be remembered is implemented as attribute visibility. We have just seen a couple of examples of attribute associativity. In C++ attribute associativity is provided via three forms of the declaration Counter c; Stack * s; ProductSpec & ps;

25. Parameter visibility – object C is passed from A to B :Sale :POST :ProductCatalog Visibility Transient visibility is not remembered, but persists only during the execution of a single method. It is implemented in one of two ways. 1: [new sale] create() 3: makeLineItem(spec, qty) 2: spec:= specification(upc) A ProductSpec object is passed to the Sale object for use by its makeLineItem method

26. Visibility Transient associations may also be implemented with locally declared visibility. Consider a method breadfirstSearch that uses an auxiliary Queue to perform a breadth first traversal of a binary tree. The lifetime of the Queue object will be within the scope of the method, and the reference need not exist outside of this method.

27. Review In designing and constructing an object-oriented system one must: • From a statement of the requirements and from the use cases identify the objects (concepts) that occur in the “problem domain” • Construct a Concept Diagram showing the static relationship (long-term associations) between concepts • Identify the concepts that are outside of the system to be built (Actors) and use Sequence Diagrams to identify the events (system operations) that they generate • For each system operation construct a contract that stipulates the state of the system before and after the operation (pre- and post- conditions) and identifies the concepts that collaborate in performing the operation • Elaboration – Review your models for lack of clarity and inconsistency

28. Review (continued) • Enhance the Concept model by exploring the associations in greater detail (roles, aggregation, generalization, link attributes, etc) and iteratively add design concepts from the solution domain (programming concepts) • Construct Collaboration diagrams (for each system operation) to detail the sequence of messages that must be exchanged to implement the task • For each message received by an object (class of objects) use a State Chart Diagram (state transition diagram) to detail the states of the system and the sequence of transitions that can occur during this operation • Continue elaboration of the models until the system is well understood and class specifications (In C++, header files) can be constructed. • Test design and specification for completeness and consistency, then begin implementing the classes.

29. Postscript I have been one acquainted with the night. I have walked out in rain – and back in rain. I have outwalked the furthest city light. I have looked down the saddest city lane. I have passed by the watchman on his beat And dropped my eyes, unwilling to explain. I have stood still and stopped the sound of feet When far away an interrupted cry Came over houses from another street, But not to call me back or say good-bye; And further still at an unearthly height, One luminary clock against the sky Proclaimed the time was neither wrong nor right. I have been one acquainted with the night. Robert Frost