UML Artifacts (Part 2)

Contents

1. Collaboration Diagrams

2. State Transition Diagrams

3. Visibility

4. Review

Collaboration Diagrams

For each system operation

identified in the Use Case 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.

Collaboration Diagrams

Actor System

System Op

Use Case Diagram

+

:ClassA

:ClassB

SystemOp

1: message1()

Collaboration Diagram

Contract

Operation:xxx

Precondition:..

Alternatively (or perhaps primarily) Sequence Diagrams can be used

instead of Collaboration Diagrams

Sequence Diagrams

Actor System

System Op

Use Case Diagram

+

Contract

Operation:xxx

Precondition:..

:ClassA :ClassB

SystemOp

message1()

Collaboration Diagram

Collaboration Diagrams

Notation

Student

class

:Student

instance

John:Student

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.

Collaboration Diagrams

Illustrating links

UML standard syntax for messages

return := message(parameter : parameterType) : returnType

optional

1: tot := total():integer:POST :Sale

sysOp()

sender receiver

Collaboration Diagrams

Illustrating Iteration

1*: [i:=0..9] str : getName(): String

SystemOp( )

CS335:ClassList:Grader

Sequence number followed by a * indicates iteration

Iteration clause is optional

sender receiver

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.

:ClassA1: message( )

Representation of a collection (multiobject)

Collaboration Diagrams

Given: A vector of StudentRecord

v: vector1: inx := find(name: String): integer

Version 1 – message to a collection (but vector is NOT a concept in the problem domain)

:StudentRecord1: inx := find(name: String): integer

Version 2 – (preferred) Emphasizes the objects in the collection, not (the solution domain) container.

Collaboration DiagramsConditional Paths – mutually exclusive messages

:ClassA :ClassB

:ClassC :ClassD

msg1( )

1a: [test] msg2( )

1b: [not test] msg4( )

1b.1: msg5( )

1a.1: msg3( )

guard – if true send msg

Collaboration Diagrams

Creating a new instance during implementation of the system operation

c: ControllerNew

m:MenuItem

:MenuItem

1: create( )

2: add(m)

Create a new MenuItem, m, and add it to the Menu

Sequence Diagrams

Sequence diagrams offer an alternate way of expressing the exchange of messages that occur between objects in an object-based system.

The notation for objects and collections is the same as used in collaboration diagrams. Time ordering is from top to bottom.

:ClassA :ClassB

msg1( )

Focus of control is illustrated with an activation box

msg2( )

msg3( )

Each message between objects is represented with a message expression on an arrowed line between the objects

Sequence Diagrams

Additional Notation

:ClassA :ClassB

msg1( )

msg2( )

msg3( )

Object creation -- let the classB object create an instance of a classC object.

:ClassCcreate( )

msg4( )

Newly created class is placed in a column starting at the level (time) of creation.

time

Sequence Diagrams

[flag = true] msg2( )

:ClassA :ClassB

msg1( )

:ClassC

Conditional message – has guard to specify the conditionMutually exclusive conditional message

[flag = false] msg3( )

Sequence Diagrams

:ClassA :ClassB

msg1( )

Iteration for a single message

*[i = 1..N] msg2( )

:ClassC

msg3( )

msg4( )

msg5( )

*[k = 1..M]

Iteration for a sequence of messages

Enclose the repeated sequence in a box, and indicate the multiplicity

Refining the Class Diagram

For every class, examine each collaboration diagram and identify

1. Every message received by an instance of that class – (these will be the methods for that class)

2. 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)

Refining the Class Diagram

methods

Class Description

Class name

Data attributes

Link attributes

Messages received

Classes to which messages are sent

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:

1. method development -- State transition diagrams provide the “blueprints” for developing the algorithms that implement methods in the class

2. 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.

State Transition DiagramsNotation

start

State 1 State 2

final state

event|output

States are represented with an oval and label

State transitions are represented with a directed arc or line

Transitions are labeled with the triggering event and the output if anySome events do not

trigger a change in state

State Transition Diagrams

Additional Notation

State Stateevent|output

[boolean condition]

Guard condition – transition occurs only if condition is true

State Transition DiagramsExample – Nested States in Telephone Call

activeidle

off hook|dial tone

[valid subscriber]

on hook

talking

do: hang upplaying dial tone

dialing connecting

digit

digit

complete|ringing

answeredThe state labeled

active has substates

State Transition Diagrams

Second Example – A Queue of Capacity Two

Size0 Size1 size2

arrival arrival

arrival | balkdeparturedeparture

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.

Description of Class Queueclass 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

}

State

State transitions

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

Visibility

Example 1. permanent, exclusive , and fixed

Consider a clock composed of three Counters (hours, mins, secs)

Clock Counter

modulus count3

*

•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

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

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.

ProductSpec Computer*describes

Visibility

(Partial) Specification of class Computer

class Computer {

private: ProductSpec & ps; public:

Computer (ProductSpec & theMod) : ps(theMod) {};

//other methods

}

The reference variable ps must be initialized in an initialization list, and cannot be reassigned during the life of the 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;

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

Transient visibility is not remembered, but persists only during the execution of a single method. It is implemented in one of two ways.

Parameter visibility – object C is passed from A to B

:ProductCatalog

:POST :Sale

2: spec:= specification(upc)

3: makeLineItem(spec, qty)

1: [new sale] create()

A ProductSpec object is passed to the Sale object for use by its makeLineItem method

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.

Review

In designing and constructing an object-oriented system one must:

1. From a statement of the requirements and from the use cases identify the objects (concepts) that occur in the “problem domain”

2. Construct a Concept Diagram showing the static relationship (long-term associations) between concepts

3. 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

4. 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

5. Elaboration – Review your models for lack of clarity and inconsistency and add or modify as necessary.

Review (continued)

6. 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)

7. Construct Sequence Diagrams or Collaboration diagrams (for each system operation) to detail the sequence of messages that must be exchanged to implement the task

8. For each relevant object (or collection of aggregates) use a State Chart Diagram (state transition diagram) to detail the states of the system and the sequence of transitions that can occur during its operation

9. Continue elaboration of the models until the system is well understood and class specifications (In C++, header files) can be constructed.

10. Test design and specification for completeness and consistency, then develop test plans and begin (or continue) implementing the classes. (an on-going process during many phases of the project)

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 beatAnd dropped my eyes, unwilling to explain.

I have stood still and stopped the sound of feetWhen far away an interrupted cryCame 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