Object-Oriented Design Lecture 13: Use Case Realizations Sharif - - PowerPoint PPT Presentation

Department of Computer Engineering

Object-Oriented Design

Lecture 13: Use Case Realizations

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Analysis Workflow: Analyze a Use Case

• The analysis workflow consists of the following activities:
• Architectural analysis
• Analyze a use case
• Outputs:
• analysis classes
• use case realizations
• Analyze a class
• Analyze a package

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Use Case Realizations

• Use case realizations show how instances of analysis classes

interact to realize the functional requirements specified by a use case.

• Each use case realization realizes exactly one use case.
• Use case realizations consist of:
• analysis class diagrams - these should "tell a story" about one (or more)

use cases;

• interaction diagrams - these demonstrate how objects interact to realize

the use case behavior;

• special requirements - you always uncover new requirements during use

case realization and you need to record these;

• use case refinement - you may need to change a use case as you begin to

realize it.

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Lifelines

• A lifeline represents a participant in an interaction - how an instance of a

classifier participates in the interaction.

• Each lifeline has an optional name, a type, and an optional selector.
• Each lifeline is drawn with the same icon as its type.
• Underline the name, type, and selector to show actual instances .

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Messages

• A message represents a specific kind of communication between two lifelines

in an interaction.

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Interaction Diagrams

• Sequence diagrams - emphasize time-ordered sequence of

message sends.

• Communication diagrams - emphasize structural relationships

between objects.

• Interaction overview diagrams - emphasize relationships

between interactions.

• Timing diagrams - emphasize real-time aspects of interactions.

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Sequence vs. Communication diagram

• Sequence Diagrams: show object interactions arranged in time

sequence, vertically

• Communication Diagrams: show object interactions arranged as a

flow of objects and their links to each other, numerically

• Semantically equivalent, structurally different
• Sequence diagram emphasize time ordering
• Communication diagrams make object linkages explicit

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Sequence Diagrams: General Notation

• Time runs top to bottom.
• Lifelines run left to right:
• lifelines have dashed vertical tails that indicate the duration of the lifeline;
• lifelines may have activations to indicate when the lifeline has focus of

control;

• rganize lifelines to minimize the number of crossing lines.
• Place explanatory scripts down the left-hand side of the sequence

diagram.

• State invariants - place state symbols on the lifeline at the appropriate

points.

• Constraints - place constraints in {} on or near lifelines.

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UML sequence diagrams

• sequence diagram: an "interaction diagram" that models a

single scenario executing in the system

• perhaps 2nd most used UML diagram (behind class diagram)
• relation of UML diagrams to others:
• CRC cards -> class diagram
• use cases -> sequence diagrams
• the axes in a sequence diagram:
• horizontal: which object/participant is acting
• vertical: time (down -> forward in time)

Sequence Diagrams: Realization Example 1

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Sequence Diagrams: Realization Example 2

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Sequence Diagrams: Realization Example 3

Use Case

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Sequence Diagrams: Realization Example 3

Sequence Diagram

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Combined Fragments

• Combined fragments - areas within a sequence diagram with

different behavior.

• The operator defines how its operands execute.
• The guard condition defines whether its operand executes.
• The operand contains the behavior.

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Combined Fragments: Operators – opt and alt

• pt - there is a single operand that executes if the condition is true (like if ...

then).

• alt - the operand whose condition is true is executed.

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Combined Fragments: Operators – opt and alt

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Combined Fragments: Operators – loop and break

• loop - loop min, max [condition]
• loop or loop * - loop forever;
• loop n, m - loop (m – n + 1) times;
• loop [ booleanExpression ] - loop while booleanExpression is true;
• loop 1, * [ booleanExpression ] - loop once then loop while

booleanExpression is true;

• loop [for each object in collectionOfObjects] - execute the body of the

loop once for each object in the collection;

• loop [for each object in className] - execute the body of the loop once for

each object of the class.

• break - if the guard condition is true, the operand is executed, not

the rest of the enclosing interaction.

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Combined Fragments: Operators – loop and break

Syntax

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Combined Fragments: Operators – loop and break

Example

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Combined Fragments: Operators – Other

• ref - the combined fragment refers to another interaction.
• par - all operands execute in parallel.
• critical - the operand executes atomically without interruption.
• seq - operands execute in parallel subject to the following constraint: events

arriving on the same lifeline from different operands occur in the same sequence as the operands occur.

• strict - the operands execute in strict sequence.
• neg - the operand shows invalid interactions.
• ignore -lists messages that are intentionally omitted from the interaction.
• consider -lists messages that are intentionally included in the interaction.
• assert - the operand is the only valid behavior at that point in the interaction.

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Example sequence diagram

sd Example loop StoreFront Cart Inventory AddItem ReserveItem PlaceItemInOrder Checkout ProcessOrder ConfirmOrder

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(De)centralized system control

• What can you say about the control flow of each of

the following systems?

• centralized?
• distributed?

Communication (aka Collaboration) Diagrams

• Communication diagrams - emphasize the structural aspects of an interaction:
• lifelines are connected by links;
• messages have a sequence number - they are numbered hierarchically according to

the nesting of the focus of control.

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Communication (aka Collaboration) Diagrams

• Objects are rectangular icons
• e.g., Order Entry Window, Order, etc.
• Messages are arrows between icons
• e.g., prepare()
• Numbers on messages indicate sequence
• Also spatial layout helps show flow
• Which do you prefer: sequence or communication?
• Fowler doesn’t use communication diagrams
• Show flow clearly, but awkward modeling alternatives

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Iteration

• Iteration - use an iteration specifier (*) and an optional iteration clause on

the message.

• The iteration clause specifies the number of times to loop.
• You can use natural language, pseudocode, source code, or sequence

diagram loop notation for the iteration clause.

• Iteration over a collection of objects:
• Denoted by showing the role name and multiplicity (>1) on the target

end of the link and prefixing the message with *.

• The message is sent to each object in turn.
• Use the parallel iteration specifier *// to indicate that messages are

executed in parallel.

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Iteration - Example

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Branching

• Branching - prefix messages with guard conditions. The message

executes if the guard condition is true.

• It can be hard to show branching clearly on a communication

diagram - for complex branching, use sequence diagrams instead.

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Communication and Class Diagrams

• Links in a communication diagram directly correlate

to associations between classes in a class diagram

Interaction Occurrences

• Interaction occurrences: references to another interaction.
• The flow of the referenced interaction is included in the flow of the

referencing interaction.

• Parameters - interaction occurrences may have parameters - use normal

parameter notation.

• Gates - inputs and outputs of interactions:
• a point on the sequence diagram frame that connects a message
• utside the frame to a message with the same signature inside the

frame.

• Use parameters when you know the source and destination of all

messages - use gates when you don't.

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Interaction Occurrences – Example

Use Case and Class Diagram

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Interaction Occurrences – Example

SDs

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Interaction Occurrences – Parameters

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Interaction Occurrences – Gates

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Communication Diagram Overview

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Sequence Diagram Overview

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Reference

• Arlow, J., Neustadt, I., UML 2 and the Unified Process: Practical Object-

Oriented Analysis and Design, 2nd Ed. Addison-Wesley, 2005.

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