2009 copyright Leslie Munday University

Realizing The Application Use Case

Analysis And Design Discipline

Leslie Munday 2008

Precursor

In order to understand the material in this course, you should have a knowledge of UML, a UML modeling tool and equivalent knowledge of the following presentations: Working With AUC Documents. Use Case Modeling Notation. Working With Class Diagrams. What Is A State Transition Diagram?

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Overview In this lesson you will learn :

how to add analysis information to a use case diagram.

how to identify classes, their attributes and relationships from the use case model.

how to discover class operations. how to map the use case to an analysis class

diagram. how to map an activity diagram to an

analysis sequence diagram. how to map state transition diagrams to

classes.

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Use Case Recap A use case comprises the following components as a

minimum: Description – High level view of the contents of the use case. Maximum Usage – How often that this use case could

potentially be executed. Primary Actor – The actor that initiates the use case. Secondary Actors – Non-initiating actors that interface with

the use case. Preconditions – The state of the system prior to the use case

executing. Basic Flow – The main or expected path the use case

executes. Alternate Flows – Alternate paths the use case may execute in

order to achieve its goal. Extension Flows – Alternate paths that cause the use case to

fail to achieve its goal. Postconditions – The possible states of the system after the

use case has completed.

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Modeling Recap The initial node takes the

name of the preconditions. A control flow takes the name

of an externally visible event. A decision describes an

alternate of extension point. A merge describes an

alternate path returning to the basic flow.

A final node describes a postcondition of the system.

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Adding Objects For every activity in the activity

diagram discover what information is input to the activity and what information is output from the activity.

Identify the appropriate object for this data and indicate whether the activity is writing to the object or reading from the object using directed object flows.

Label the object flow with the name of the data.

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Dematerializer Objects 1

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Dematerializer Objects 2

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The Objects Notice that the objects take the name of the

‘real-life’ object that they interface with. door – operates the door to the dematerializer. transmitter – interfaces to the Transmitter actor. cargoHandler – controls securing the cargo. vacuumPump – controls removing air. deconstructor – controls the heart of the

dematrializer. blueprintManager – is an interface to the

BlueprintManger actor. airSensor – monitors the air pressure. airValve – controls the air pressure. powerManager – controls the power to the

dematerializer.

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Class Diagram

Create a class diagram and copy the object classes onto the diagram.

Add the operations and data from the activity diagram to the classes.

Connect the classes with relationships and add new classes as required.

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Dematerializer Class Diagram

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The Cargo class has been added to identify the attributes of the cargo. These will be input to the system as parameters of the ‘deconstruct’ command.

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Draw A Sequence Diagram Create a sequence diagram. Add an instance of the primary actor of the use

case on the left side of the sequence diagram. Add instances of secondary actors on the right

side of the sequence diagram. Place instances of the classes on the diagram,

roughly in the sequence in which they are accessed by the use case.

For every control flow in the basic flow of the use case activity diagram, draw equivalent message flows on the sequence diagram.

Add operations, as necessary, to the classes that represent the messages on the sequence diagram.

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Corresponding Sequence Diagram

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Sequence Diagram Explained

The sequence diagram is only complete up to step 5 of the use case.

Notice that the Cargo object is used to control the internal messages between the other objects.

Because the sequence diagram implies a time scale running vertically down the page, it is very difficult to show parallel flows on a sequence diagram.

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Updated Class Diagram The

cargo class has been updated to reflect the operations discovered on the sequence diagram.

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Alternative and Extending Flows

Repeat drawing a sequence diagram for each alternative and extending flow.

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State Transition Diagrams Another tool that helps us to determine if

there is any missing data or operations from our model, is the STD.

For each class in the class diagram, where its states are non-trivial, i.e. there is more than one state, create a STD.

Identify all of the possible states that the class may take and all potential transitions between those states.

Ensure that all data and operations used by the STD are captured within the class that the STD is modeling.

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AirValve STD

Notice that from the class diagram we see 2 states, ‘Open’ and ‘Closed’.

Once we start modeling, we discovered another 2 states and a potential data element, ‘failed’.

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Update The Class Diagram

We have added a ‘failureState’ attribute to the valve class.

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Revisit the Use Case Activity The use case did not consider what to do if the air

valve failed. We need to add an alternate path to the use case

describes the action to be taken in the event of a valve failure, extension point A3.

Notice the new extension does not mention the valve, it abstracts the functionality to the vacuum equipment without stating what that comprises.

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Extension Points•A3 Vacuum equipment broke:•12 At step 6 the system cannot create a vacuum, the system unsecures the cargo.•13. When the cago is released the system opens the door.The use case ends.

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Summary

In this presentation you learned: how to add objects to a use case activity diagram. how to convert those objects into classes on a class

diagram, and add preliminary data and operations. how to model the use case and its associated classes

using sequence diagrams. how the sequence diagrams are used to capture more

detailed operations of the classes. how to model a class with a STD. how to identify more information for the class diagram

from the events in the STD. how to add identify functionality from a use case by

analyzing the classes that implement the use case.

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Test Your Knowledge Add objects to the ATM example use case. Create a class diagram for the ATM

application. Create a sequence diagram for each path

through the ATM application use case. Model the ATM classes with STDs. Update the use case from operations that

are discovered during the modeling process.

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