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CS 451 Software Engineering

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Yuanfang Cai

Room 104, University Crossings

215.895.0298

yfcai@cs.drexel.edu

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Elaboration

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Elaboration: Building the Analysis Model An analysis model provides a description of the

required information, functional , and behavioral domains for a computer based system.

An analysis model will change during the requirements gathering with some areas stable and others being volatile.

There are many ways to represent the model. Software is not visualizable

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Domain Analysis Sources of domain knowledge

Technical literature Existing application Customer surveys Expert advice Current/future requirements

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Analysis Modeling Goals Describe what the customer requires

Establish a basis for the creation of a software

design Define a set of requirements that can be

validated once the software is built

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Deeper understanding the requirements From SRS, e.g. use case scenarios:

What are the entities in the system? Class diagrams Data-flow diagram

How these entities interact with each other? Sequence diagram Activity diagram Swim lane diagram

The behavior of a complex object State diagram

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Analysis Modeling Approaches

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Analysis Modeling

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Scenario based modeling Use cases –text Use case diagrams Activity diagram

Visualizing the logic within a use case: scenarios Swim lane diagram

Split activities among actors.

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Scenario-based Modeling Write Use-Cases Develop an Activity Diagram

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An Activity Diagram

Similar to a flowchart: Round rectangles

imply specific system functions

Arrows represent flow through the system

Diamonds depict a branching decision

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Swim Lane Diagram

Swim Lane Diagram

Represents flow of activities indicating which actor has responsibility for the action.

Responsibilities are represented as parallel segments that divide the diamond vertically, like the lanes in a swimming pool.

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Class based modeling Class diagram

Entities Attributes Behaviors

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Elaborating Use Cases Each usage scenario implies a set of “objects”

that are manipulated as an actor interacts with them

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Elaborating Use Cases The behavior of a computer- based system can have a

profound effect on the design that is chosen, therefore the analysis model must provide modeling elements that depict behavior:

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Class-Based Modeling Class diagram for the system class

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Class Diagram

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Class

A class encapsulates state (attribute) and behavior (operations). Each attribute has a type. Each operation has a signature. The class name is the only mandatory information.

name

attributes

operations

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Generalization

Generalization relationships denote inheritance between classes.

The children classes inherit the attributes and operations of the parent class.

Indicated by a hollow arrow

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Association • Indicated by a solid arrow line from the source class to the target class • Can be bi-directional represented by lines without arrow heads

Don’t usually put the association down as an attribute in the class

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Aggregation

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•If the association conveys the information that one object is part of another object (“has-a”), but their lifetimes are independent (they could exist independently).

•Aggregation is stronger than association, unidirectional.

•There is a container and one or more contained objects. For •example, we may say that “a Department contains a set of Employees,” or that “a Faculty contains a set of Teachers.”

•An aggregation relationship is indicated by placing a white diamond at the end of the association next to the aggregate class.

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Composition

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•Even stronger than aggregation is composition. There is composition when an object is contained in another object, and it can exist only as long as the container exists and it only exists for the benefit of the container.

•Examples of composition are the relationship Invoice-Invoice Line, and Drawing-Figure.

•A composition is shown by a black diamond on the end of association next to the composite class.

•An aggregation is a special form of association; composition is a stronger form of aggregation.

•Both aggregation and composition are a part-whole hierarchy.

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Multiplicity

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Candidate classes: Noun extraction Company XYZ has two types of customers,

corporate customers and personal customers. All customers can place orders. Every order is placed by a customer.

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Evaluating a Class/Class Diagram

?? 1. Intention-revealing naming: Does the name of the object

convey its abstractions? Does the abstraction have a natural meaning and use in the domain?

2. Single Responsibility: Do the name, main responsibility statement data and functions align?

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Flow-Oriented Modeling Data Flow Diagrams show the input-process-output

view of a system.

DFD’s are not part of UML, but a complement to UML.

There is a natural tendency to show too much detail too soon.

Start at a high level and work your way down one process at a time.

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Flow-Oriented Modeling DFD for the SafeHome Security function

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Flow-Oriented Modeling Level 1 DFD for SafeHome Security Function

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Flow-Oriented Modeling Level 2 DFD that refines the monitor sensors process

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Behavioral Models

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Sequence Diagram How the entities interact with each other For further design analysis

State Diagram How a complex object behaves

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UML Sequence Diagrams

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UML Sequence Diagrams Used during requirements analysis

To refine use case descriptions To find additional objects (“participating

objects”)

Used during system design to refine subsystem interfaces Performance analysis

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A Sample Scenario A player rolls the dice and gets a 6. The player moves 6 cells. The player lands on a cell that is an un-owned property. The player’s turn is over. Not all nouns become objects such as “turn”

Objects Player Dice Cell Property

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UML Sequence Diagrams Objects are represented by columns (first column is actor that

initiates use case) Messages are represented by arrows Activations of an operation are represented by narrow rectangles

No significance to the horizontal orderings of the objects Return values are optionally indicated using a dashed arrow with a label indicating the return value Suggestion: not to indicate the return values when it is obvious what is being returned

Player Dice Cell Property

rollDice

DiceValue(6)

MoveCell(6)

isOwnedProperty

isOwnedProperty(False)

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Scenario A player rolls the dice and gets a 6. The player moves 6 cells. The player lands on a cell that is an un-owned property. The player’s turn is over.

Player Dice Cell Property

rollDice

DiceValue(6)

MoveCell(6)

isOwnedProperty

isOwnedProperty(False)

Not all nouns become objects such as “turn”

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Conditional Logic

Player Dice Cell Property

rollDice

DiceValue(n)

MoveCells(n)

[isOwnedProperty]

isOwnedProperty(False)

isOwnedProperty(True,owner)

Owner

PayOwner

[else]

• If the player lands on a cell that is an un-owned property, the player’s turn is over. • If the player lands on a cell that is owned, the player must pay rent to the owner of the property. • Then, the player’s turn is over.

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UML State Diagram

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State Diagram A state diagram (also called state machine diagram) depict the

various states that an object may be in and the transitions between those states.

Appropriate to be developed for complex objects.

From UML Distilled (pp. 107-108): A lock in a haunted house: keep valuables in a safe that’s hard to find

To reveal the lock to the safe, I have to remove a strategic candle from its holder, but this will reveal the lock only while the door is closed. In the Wait state, if the candle is removed providing the door is closed, you reveal the lock and move to the Lock state. Once I can see the lock, I can insert my key to open the safe. For extra safety, I make sure that I can open the safe only if I re-place the candle first. If a thief neglects this precaution, I’ll unleash a killer rabbit to him.

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State Diagram From UML Distilled (pp. 107-108): A lock in a haunted house: keep valuables in a safe that’s hard to find

To reveal the lock to the safe, I have to remove a strategic candle from its holder, but this will reveal the lock only while the door is closed. In the Wait state, if the candle is removed providing the door is closed, you reveal the lock and move to the Lock state. Once I can see the lock, I can insert my key to open the safe. For extra safety, I make sure that I can open the safe only if I re-place the candle first. If a thief neglects this precaution, I’ll unleash a killer rabbit to him.

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States States are represented by the values of the attributes or data members of an object.

Initial state

state

Terminal state

transition

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Transitions •Transitions are the result of the invocation of a method that causes an important change in state.

•Each transition has a label that comes in three parts. All the parts are optional.

trigger-signature [guard]/activity

candle removed [door closed]/reveal lock

•The trigger-signature is usually a single event that triggers a potential change of state.

•Missing trigger-signature [rare] – you take the transition immediately.

•The guard, if present, is a Boolean condition that must be true for the transition to be taken.

•Missing guard – always take the transition.

•The activity is some behavior that’s “executed” during the transition. •Missing activity – don’t do anything during the transition.

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trigger-signature: event that causes a potential change of state

guard: Boolean condition that must be true for transition to happen

activity: behavior that’s executed during the transition

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Rules for State Diagrams There is one initial state (can be multiple final states). Every state can be reached from the initial state. From each state, there must be a path to a final state. Every transition between states must be labeled with an

event that will cause that transition. When an event occurs, you can take only one transition.

If you have multiple transitions with the same event, the guards must be mutually exclusive.

Transitions that are not shown are illegal OR show transitions that cause errors.