Interaction Diagrams - Chapter 15

Describe/illustrate sequence of message exchanges among objects

•show the flow of control across many objects

•used to illustrate a use case, a scenario, ...

Types

•Collaboration diagram

•Sequence diagram

Interaction Diagrams

Message

•asynchronous or synchronous

•components

•numbered (collaboration diagram)

•guard

•name

•parameter list

•name is mandatory ... others as required

Interaction Diagrams

• Synchronous vs asynchronous messages

• We will assume (at first) that all messages are synchronous:

• if object A sends a message to object B then A is suspended

• object B gains control, and B begins to compute

• object A waits until B responds (i.e. B sends a message back to A)

•When an asynchronous message is sent from A to B, A does not pause and wait for B to finish … results in multiple threads of control.

Interaction Diagrams

Synchronous messages:

•control, or the ability to compute, is gained by holding a token that is passed with a message

• consider that there is an activation stack:

• when object A sends a message to object B, object B goes on to the top of the stack and it can compute. If B responds to A then B is popped from the stack and A, being at the top, begins to compute

Collaboration Diagram

•Objects are represented similarly to classes in a class model … relationships are indicated clearly

•Objects may be named or unnamed

•Timing is understood by the numbering scheme. We use a nested decimal numbering to indicate the order in which messages are sent

•Many messages may be sent across one link

Figure 15.3 Collaboration diagram for makePayment

Figure 15.7 Messages

Figure 15.8 Message to ‘this’

Figure 15.9 Instance creation

Figure 15.10 Sequence Numbering

Figure 15.11 Complex numbering

Figure 15.12 Conditional Message

Figure 15.13 Mutually exclusive messages

Figure 15.14 Iteration

Figure 15.15 Iteration over a multiobject

Figure 15.16 Messages to a class itself, not an object

Collaboration Diagram - example

Suppose we have classes for POrder, Customer, LineItem, Product with the following class model

POrder

LineItem Product

Customer1

10..*0..*

1

0..*

We want to exhibit how objects of these classes communicate in order for the POrder to learn its value

Collaboration Diagram - example

Suppose

•POrder does not know its value.

•To determine its value it must ask each of its line items “what are you worth?”, and then ask the customer “what discount do you get”.

•Each line doesn’t remember the corresponding products price and so it must interrogate the product to determine the price

POrder

LineItem Product

Customer1

10..*0..*

1

0..*

Collaboration Diagram

128937:POrder

line1:LineItem TYZMonitor:Product

line2:LineItem OptMouseX :Product

JonesSupply:Customer

1:cost:=reportTotal()

1.1:price:=reportPrice()

2:reportTotal()

2.1:price:=reportPrice()

3:discount:=reportDiscount()

reportTotal()

Given that the objects below are involved, we show them along with the basic associations

Since these are objects, not classes, there are no multiplicities

Some message starts things off

Collaboration Diagram

•Use the diagramming technique to show the complexity you need to understand or represent

•Example: consider the creation of the lines of a Purchase Order, and where

•we are checking for adequate stock on hand•we reorder if we fall below a reorder quantity - a reorder item line is created•if there’s enough on hand, a delivery line item gets created and quantity on hand must be decremented

Collaboration Diagram - example

128937:POrder

:LineItem

:DeliveryItem {new}

1*[for all order lines]: prepare()

1.1:reportPrice()1.2:[hasStock]:=remove()

1.2.1:needsToReorder:=needToReorder()

1.2.2:[needsToReorder]:create1.3:[hasStock]:=create

:Product

:ReorderItem {new}