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: Cashier:System

addLineItem(itemID, quantity)

endSale()

makePayment(amount)

description, total

total with taxes

change due, receipt

* [more items]

makeNewSale()

these input system eventsinvoke system operations

the system eventmakeNewSale invokes asystem operation calledmakeNewSale and so forth

this is the same as in object-oriented programming whenwe say the message fooinvokes the method (handlingoperation) foo

SSD for a samplePOS Use Case Figure 13.1Input Events invoke a system operation of the same name

same idea as in object-oriented programming when we say a message foo invokes the method foo

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: Cashier:System

addLineItem(itemID, quantity)

endSale()

makePayment(amount)

description, total

total with taxes

change due, receipt

* [more items]

makeNewSale()

these input system eventsinvoke system operations

the system eventmakeNewSale invokes asystem operation calledmakeNewSale and so forth

this is the same as in object-oriented programming whenwe say the message fooinvokes the method (handlingoperation) foo

SSD for a samplePOS Use Case Figure 13.1Input Events invoke a system operation of the same name

same idea as in object-oriented programming when we say a message foo invokes the method foo

We’ll refer to this as the enterItem system operation

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Messages sent for enterItem( … ) Figures 17.8, 20.6

This diagram shows a collaboration among objects. The collaboration is a sequence of messages. They occur in response to the system event enterItem.

We’ll explain this diagram, but note that we’ll study the notation more thoroughly in future lectures

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Messages sent for enterItem( … ) Figures 17.8, 20.6

The messages are sent in the order: 1, 1.1, 2, 2.1, 2.2.

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Messages sent for enterItem( … ) Figures 17.8, 20.6

The diagram would be created if the designer thought the illustration would be useful … to communicate to someone how the system will work.

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Messages sent for enterItem( … ) Figures 17.8, 20.6

The system operation is received by the Register object. On page 314 you’ll note that Register has an enterItem method.

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Messages sent for enterItem( … ) Figures 17.8, 20.6

The register object sends a message to the product catalogue. (The register will eventually tell the sale object to create a line for this.)

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Messages sent for enterItem( … ) Figures 17.8, 20.6

The catalogue will search the catalogue data structure for the item that was scanned at the register.

Note that on Page 314 the Java code only has to invoke the get method for the HashMap.

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Messages sent for enterItem( … ) Figures 17.8, 20.6

The sale object is sent a message that will cause it to create a new sales line

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Messages sent for enterItem( … ) Figures 17.8, 20.6

A new sales line is created

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Messages sent for enterItem( … ) Figures 17.8, 20.6

The newly created sales line will be added to the collection of lines belonging to this sale.

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Domain Model

Use Case Model

•text

•diagram

•SSD

•System operation contracts

Design Model

Figure 13.3

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Contracts

A technique for describing system operations in terms of state changes to objects in a Domain Model

major proponent - Bertrand Meyer

based on concept of assertion

•a statement, a declaration, that must be true

•a false value indicates a bug

•UML has OCL - very formal syntax which we will ignore

•at the requirements gathering stage, these are informal and likely incomplete

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Contracts

Contract Components

Operation - name and parameters

Cross References - where operation used

Preconditions - assumptions about the state of the system or Domain Model objects

Postconditions - state of objects after the operation completes

•objects:any new ones? any attributes modified?

•associations: any new or modified associations?

Larman’s version is very informal - focus on what, not how

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SalesLineItem

quantity

Product Specification

itemID

Sale

1

1..*

*1Described by

Contained in

The part of the Domain Model that is relevant to enterItem( )

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Contracts

Example

Operation enterItem (itemID : ItemID, quantity : integer)

Cross References Use Case Process Sale

Preconditions There is a sale underway

Postconditions

- a SalesLineItem instance was created

- an association between the sale and the sales line item was created

- an attribute, quantity, was modified

- an association between the product specification and the sales line item was created

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OCL

Object Constraint Language

• UML has a formal language for specifying constraints on object-oriented models

context Salesperson:: sell ( item: Thing ) : Real

pre: self.sellableItems -> includes (item)

post: not self.sellableItems -> includes (item) and result=item.price

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Ch 15. Interaction Diagrams

Now, we are shifting towards design - how do the objects in the model interact?

Interaction Diagram - illustrates how objects collaborate to fulfill requirements - the messages that are sent from one object to another

•collaboration diagrams

•sequence diagrams

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SalesLineItem

quantity

Product Specification

itemID

Sale

makePayment()

1

1..*

*1Described by

Contained in

More of the Domain Model - we’ve included some methods

Register

makePayment()

Payment

create()

1*

1

1

Captured on

Paid by

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Figure 15.3 Collaboration Diagram

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Figure 15.4 Sequence Diagram