CS 451 Software Engineering Yuanfang Cai Room 104, University - - PowerPoint PPT Presentation

Drexel University

CS 451 Software Engineering

1

Yuanfang Cai Room 104, University Crossings 215.895.0298 yfcai@cs.drexel.edu

Drexel University

Elaboration

2

Drexel University

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

3

Drexel University

Domain Analysis



Sources of domain knowledge



Technical literature



Existing application



Customer surveys



Expert advice



Current/future requirements

4

Drexel University

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

5

Drexel University

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

6

Drexel University

Analysis Modeling Approaches

7

Drexel University

Analysis Modeling

8

Drexel University

9

Drexel University

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.

10

Drexel University

Scenario-based Modeling



Write Use-Cases



Develop an Activity Diagram

11

Drexel University

An Activity Diagram

 Similar to a flowchart:

 Round rectangles

imply specific system functions

 Arrows represent

flow through the system

 Diamonds depict a

branching decision

12

Drexel University

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.

13

Drexel University

Class based modeling

 Class diagram

 Entities  Attributes  Behaviors

14

Drexel University

Elaborating Use Cases

 Each usage scenario implies a set of “objects”

that are manipulated as an actor interacts with them

15

Drexel University

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:

16

Drexel University

Class-Based Modeling

 Class diagram for the system class

17

Drexel University

Class Diagram

Drexel University

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.

nam e attributes

• peration

s

Drexel University

Generalization



Generalization relationships denote inheritance between classes.



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



Indicated by a hollow arrow

Drexel University

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

Drexel University

Aggregation

22

• 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.

Drexel University

Composition

23

• 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.

Drexel University

Multiplicity

Drexel University

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.

Drexel University

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?

Drexel University

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.

27

Drexel University

Flow-Oriented Modeling

 DFD for the SafeHome Security function

28

Drexel University

Flow-Oriented Modeling

 Level 1 DFD for SafeHome Security Function

29

Drexel University

Flow-Oriented Modeling



Level 2 DFD that refines the monitor sensors process

30

Drexel University

Behavioral Models

31

 Sequence Diagram

 How the entities interact with each other  For further design analysis

 State Diagram

 How a complex object behaves

Drexel University

UML Sequence Diagrams

32

Drexel University

UML Sequence Diagrams

 Used during requirements analysis

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

• bjects”)

 Used during system design

 to refine subsystem interfaces  Performance analysis

Drexel University

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

Drexel University

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)

Drexel University

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”

Drexel University

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-
• wned 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.

Drexel University

UML State Diagram

38

Drexel University

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.

Drexel University

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.

Drexel University

States

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

Initial state state Terminal state transition

Drexel University

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
• ptional.

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.

Drexel University

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

Drexel University

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.