1

Chapter 8Analysis Modeling

Adapted by Dan Fleck from:- Roger Pressman’s Slides- http://www.informatics.sussex.ac.uk/users/lb203/se/SE04.pdf- Jochen Rick’s slides from GA Institute of Technology- http://webfuse.cqu.edu.au/Courses/aut2001/95169/

Extra_Examples/DFD_Example_1/- System Analysis and Design slides edited by Yale Braunstein

2

Requirements Analysis Requirements analysis

specifies software’s operational characteristics indicates software's interface with other system elements establishes constraints that software must meet

Requirements analysis allows the software engineer (called an analyst or modeler in this role) to: elaborate on basic requirements established during earlier

requirement engineering tasks build models that depict user scenarios, functional activities,

problem classes and their relationships, system and class behavior, and the flow of data as it is transformed.

3

Analysis Phase: What is it?

systemdescription

analysismodel

designmodel

Three objectives:

• To describe what the customer requires

• To establish a basis for the creation of a software design

• To define a set of requirements that can be validated once the software is built

Three objectives:

• To describe what the customer requires

• To establish a basis for the creation of a software design

• To define a set of requirements that can be validated once the software is built

4

Analysis Modeling Approaches

Structural analysis: The data: The model defines their attributes and

relationships. The processes that transform the data: The

model shows how they transform the data objects as they flow through the system.

Object-oriented analysis: Focus: Classes and their inter-relationships UML is predominantly object-oriented

But don’t be to dogmatic!

5

Elements of the Analysis Model

Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams

Scenario-based elements

Class diagrams

Analysis Packages

CRC Models

Collaboration Diagrams

Class-based elements

Data-flow diagrams

Control flow diagrams

Processing narratives

Flow-oriented elements

State diagrams

Sequence diagrams

Behavioral elements

Analysis Model

6

Data Modeling

examines data objects independently of processing

focuses attention on the data domain

creates a model at the customer’s level of abstraction

indicates how data objects relate to one another

7

What is a Data Object?

ObjectObject ——something that is described by a setsomething that is described by a setof attributes (data items) and that will be of attributes (data items) and that will be manipulated within the software (system)manipulated within the software (system)

each each instanceinstance of an object (e.g., a book) of an object (e.g., a book) can be identified uniquely (e.g., ISBN #) can be identified uniquely (e.g., ISBN #)

each plays a necessary role in the systemeach plays a necessary role in the systemi.e., the system could not function without i.e., the system could not function without access to instances of the objectaccess to instances of the object

each is described by attributes that are each is described by attributes that are themselves data itemsthemselves data items

What are some typical data objects?

8

Typical Data Objects

external entitiesexternal entities (printer, user, sensor)(printer, user, sensor)thingsthings (e.g, reports, displays, signals) (e.g, reports, displays, signals) occurrences or eventsoccurrences or events (e.g., interrupt, alarm)(e.g., interrupt, alarm)rolesroles (e.g., manager, engineer, salesperson)(e.g., manager, engineer, salesperson)organizational unitsorganizational units (e.g., division, team)(e.g., division, team)placesplaces (e.g., manufacturing floor) (e.g., manufacturing floor)

structuresstructures (e.g., employee record)(e.g., employee record)

9

Data Objects and Attributes

A data object contains a set of attributes that A data object contains a set of attributes that act as an aspect, quality, characteristic, or act as an aspect, quality, characteristic, or descriptor of the objectdescriptor of the object

object: automobileobject: automobileattributes:attributes: makemake modelmodel body typebody type priceprice options codeoptions code

How do data objects differ from OO classes or do they?

10

What is a Relationship?

relationshiprelationship ——indicates “connectedness”; indicates “connectedness”; a "fact" that must be "remembered" a "fact" that must be "remembered" by the system and cannot or is not computed by the system and cannot or is not computed or derived mechanicallyor derived mechanically

several instances of a relationship can exist objects can be related in many different ways

11

ERD Notation

(0, m) (1, 1)

objectobject objectobjectrelationshiprelationship11 22

One common form:One common form:

(0, m)(0, m)

(1, 1)(1, 1)

objectobject11 objectobject22relationshiprelationship

Another common form:Another common form:attributeattribute

See http://www.smartdraw.com/tutorials/software/erd/tutorial_01.htm for a tutorial on how to draw entity relationship diagrams.

12

The ERD: An Example

(1,1)(1,1) (1,m)(1,m)placesplacesCustomerCustomer

requestrequestfor servicefor service

generatesgenerates (1,n)(1,n)

(1,1)(1,1)

workworkorderorder

workworktaskstasks

materialsmaterials

consistsconsistsofof

listslists

(1,1)(1,1)(1,w)(1,w)

(1,1)

(1,i)(1,i)

selectedselectedfromfrom

standardstandardtask tabletask table

(1,w)(1,w)

(1,1)(1,1)

13

The Flow Model

Every computer-based system is an Every computer-based system is an information transform ....information transform ....

computercomputerbasedbased

systemsysteminputinput outputoutput

14

Flow Modeling Notation

external entityexternal entity

processprocess

data flowdata flow

data storedata store

15

External Entity

A producer or consumer of dataA producer or consumer of data

Examples: a person, a device, a sensorExamples: a person, a device, a sensor

Another example: computer-basedAnother example: computer-basedsystemsystem

Data must always originate somewhereData must always originate somewhereand must always be sent to somethingand must always be sent to something

16

Process

A data transformer (changes inputA data transformer (changes inputto output)to output)

Examples: compute taxes, determine area,Examples: compute taxes, determine area,format report, display graph format report, display graph

Data must always be processed in some Data must always be processed in some way to achieve system functionway to achieve system function

17

Data Flow

Data flows through a system, beginningData flows through a system, beginningas input and be transformed into output.as input and be transformed into output.

computecomputetriangle triangle

areaarea

basebase

heightheight

areaarea

18

Data Stores

DataData is often stored for later use.is often stored for later use.

look-uplook-upsensorsensor

datadata

sensor #sensor #

report requiredreport required

sensor #, type, sensor #, type, location, agelocation, age

sensor datasensor data

sensor numbersensor number

type, type, location, agelocation, age

19

Data Flow Diagramming:Guidelines

all icons must be labeled with meaningful names

the DFD evolves through a number of levels of detail

always begin with a context level diagram (also called level 0)

always show external entities at level 0 always label data flow arrows do not represent procedural logic

20

Constructing a DFD—I

review the data model to isolate data objects and use a grammatical parse to determine “operations”

determine external entities (producers and consumers of data)

create a level 0 DFD

21

Level 0 DFD Examplesuseruser

processing processing requestrequest

videovideosourcesource NTSCNTSC

video signalvideo signal

digitaldigitalvideovideo

processorprocessor

requestedrequestedvideovideosignalsignal

monitormonitor

22

Constructing a DFD—II

write a narrative describing the transform

parse to determine next level transforms

“balance” the flow to maintain data flow continuity

develop a level 1 DFD use a 1:5 (approx.) expansion ratio

23

The Data Flow Hierarchy

PPaa bbxx yy

p1p1p2p2

p3p3p4p4 55

aa

bb

cc

ddee

ff

gg

level 0level 0

level 1level 1

24

Example DFD: Level 1

25

DFD: A practical example

Launched Dec. 11, 1998, the Climate Orbiter plunged too steeply into the Martian atmosphere Sept. 23, 1999, and either burned up or crashed. In an initial failure report released Oct. 15, 2000 the review board blamed the navigation error on a communications foul-up between NASA's Jet Propulsion Laboratory and prime contractor Lockheed Martin.

Launched Dec. 11, 1998, the Climate Orbiter plunged too steeply into the Martian atmosphere Sept. 23, 1999, and either burned up or crashed. In an initial failure report released Oct. 15, 2000 the review board blamed the navigation error on a communications foul-up between NASA's Jet Propulsion Laboratory and prime contractor Lockheed Martin.

Collect,analyze,

generate flightcontrol data

JPL-1

J1 JPL store

Convert datafrom Metric to

English

?

LM1 LM store

Controlspaceflight

LM-1

English data

Transfer of Flight Control DataThis processwas missing

Metric data

Transfer data

?

Who wasresponsible

for this task?

26

Flow Modeling Notes

each bubble is refined until it does just one thing

the expansion ratio decreases as the number of levels increase

most systems require between 3 and 7 levels for an adequate flow model

a single data flow item (arrow) may be expanded as levels increase (data dictionary provides information)

27

Activity DiagramSupplements the use-case Supplements the use-case by providing a diagrammatic by providing a diagrammatic representation of procedural representation of procedural flowflow

How might we make this How might we make this better?better?

enter passwordand user ID

select major function

valid passwords/ID

prompt for reentry

invalid passwords/ID

input tries remainno inputtries remain

select surveillance

other functionsmay also beselected

thumbnail views select a specific camera

select camera icon

prompt foranother view

select specificcamera - thumbnails

exit this function see another camera

view camera outputin labelled window

28

Swimlane Diagrams

Allows the modeler to Allows the modeler to represent the flow of represent the flow of activities described by the activities described by the use-case and at the same use-case and at the same time indicate which actor time indicate which actor (if there are multiple (if there are multiple actors involved in a actors involved in a specific use-case) or specific use-case) or analysis class has analysis class has responsibility for the responsibility for the action described by an action described by an activity rectangleactivity rectangle

enter passwordand user ID

select major functionvalid passwords/ID

prompt for reentry

invalidpasswords/ID

input triesremain

no inputtries remain

select surveillance

other functionsmay also beselected

thumbnail views select a specific camera

select camera icon

generate videooutput

select specificcamera - thumbnails

exit thisfunctionsee

anothercamera

homeowner camera interface

prompt foranother viewview camera output

in labelled window

29

Activity Diagram Example

- To show concurrent activity, activity diagrams allow branches and joins.

- You can also reference or include other activity diagrams

30

Lets Try It

Lets create a swimlane activity diagram for opening a Lemonade stand.

31

Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams

Scenario-based elements

Class diagrams

Analysis Packages

CRC Models

Collaboration Diagrams

Class-based elements

Data-flow diagrams

Control flow diagrams

Processing narratives

Flow-oriented elements

State diagrams

Sequence diagrams

Behavioral elements

Analysis Model

Elements of the Analysis ModelOnward to data flow diagrams!

32

Flow-Oriented Modeling

Represents how data objects are transformed at they Represents how data objects are transformed at they move through the systemmove through the system

A A data flow diagram (DFD)data flow diagram (DFD) is the diagrammatic form that is the diagrammatic form that is usedis used

Considered by many to be an ‘old school’ approach, flow-Considered by many to be an ‘old school’ approach, flow-oriented modeling continues to provide a view of the oriented modeling continues to provide a view of the system that is unique—it should be used to supplement system that is unique—it should be used to supplement other analysis model elementsother analysis model elements

33

Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams

Scenario-based elements

Class diagrams

Analysis Packages

CRC Models

Collaboration Diagrams

Class-based elements

Data-flow diagrams

Control flow diagrams

Processing narratives

Flow-oriented elements

State diagrams

Sequence diagrams

Behavioral elements

Analysis Model

Elements of the Analysis Model

Oh behave!

34

Behavioral Modeling The behavioral model indicates how software will

respond to external events or stimuli. To create the model, the analyst must perform the following steps:

Evaluate all use-cases to fully understand the sequence of interaction within the system.

Identify events that drive the interaction sequence and understand how these events relate to specific objects.

Create a sequence for each use-case. Build a state diagram for the system. Review the behavioral model to verify accuracy and

consistency.

35

State Representations In the context of behavioral modeling, two different

characterizations of states must be considered: the state of each class as the system performs its function and the state of the system as observed from the outside as the

system performs its function The state of a class takes on both passive and active

characteristics [CHA93]. A passive state is simply the current status of all of an object’s

attributes. The active state of an object indicates the current status of the

object as it undergoes a continuing transformation or processing.

36

State Diagram for the ControlPanel Class

reading

locked

selecting

passwordentered

comparing

password = incorrect& numberOfTries < maxTries

password = correct

activation successful

key hit

do: validatePassword

numberOfTries > maxTries

timer < lockedTime

timer > lockedTime

37

The States of a System state—a set of observable

circumstances that characterizes the behavior of a system at a given time

state transition —the movement from one state to another

event —an occurrence that causes the system to exhibit some predictable form of behavior

action —process that occurs as a consequence of making a transition

38

Behavioral Modeling

make a list of the different states of a system (How does the system behave?)

indicate how the system makes a transition from one state to another (How does the system change state?) indicate event indicate action

draw a state diagram or a sequence diagram

39

State Diagram - Lets Try It!You are designing a traffic light system for this intersection.

Draw a state diagram showing the different states and how they transition.

North

South

East

West

40

Use-case diagrams

Use cases - text

Activity Diagrams

Swim lane diagrams

Scenario-based elements

Class diagrams

Analysis Packages

CRC Models

Collaboration Diagrams

Class-based elements

Data-flow diagrams

Control flow diagrams

Processing narratives

Flow-oriented elements

State diagrams

Sequence diagrams

Behavioral elements

Analysis Model

Elements of the Analysis Model

Onward to Class-based elements!

41

Object Oriented Analysis (OOA)

The intent of OOA is to define all classes (and the relationships and behavior associated with them) that are relevant to the problem to be solved. For that, a number of tasks must occur:

1. Classes must be identified (i.e., attributes and methods)

2. A class hierarchy is defined

3. Object-to-object relationships should be represented

4. Object behavior must be modeled

5. Tasks 1 through 4 are reapplied iteratively

42

Object-Oriented Concepts What are the basic object oriented

concepts?

43

Object-Oriented Concepts What are the basic object oriented

concepts?

Classes and objects Attributes and operations Encapsulation and instantiation Inheritance

44

Encapsulation/HidingThe object encapsulates

both data and the logicalprocedures required tomanipulate the data

Achieves “information hiding”

method # 1

data

method # 2

method # 4

method # 5

method # 6

method # 3

45

Scenario Based Modeling: Use-Cases

a scenario that describes a “thread of usage” for a system

actors represent roles people or devices play as the system functions

users can play a number of different roles for a given scenario

““[Use-cases] are simply an aid to defining what [Use-cases] are simply an aid to defining what exists outside the system (actors) and what exists outside the system (actors) and what should be performed by the system (use-cases).” should be performed by the system (use-cases).” Ivar JacobsonIvar Jacobson

46

Class-Based Modeling Identify analysis classes by examining

the problem statement Use a “grammatical parse” to isolate

potential classes Identify the attributes of each class Identify operations that manipulate the

attributes

47

Domain AnalysisSoftware domain analysis is the identification, Software domain analysis is the identification, analysis, and specification of common analysis, and specification of common requirements from a specific application requirements from a specific application domain, typically for reuse on multiple projects domain, typically for reuse on multiple projects within that application domain . . . within that application domain . . .

What is object oriented domain analysis then?What is object oriented domain analysis then?

48

Domain AnalysisSoftware domain analysis is the identification, Software domain analysis is the identification, analysis, and specification of common analysis, and specification of common requirements from a specific application requirements from a specific application domain, typically for reuse on multiple projects domain, typically for reuse on multiple projects within that application domain . . . within that application domain . . .

Object-oriented domain analysis is the Object-oriented domain analysis is the identification, analysis, and specification of identification, analysis, and specification of common, common, reusablereusable capabilitiescapabilities within a within a specific application domain, in terms of specific application domain, in terms of commoncommon objectsobjects, classes, subassemblies, , classes, subassemblies, and frameworks . . .and frameworks . . . Donald Firesmith

49

Grammatical Parsing

Write an informal description of the problem. The

customer requirements document is one such

description.

Underline all nouns in the description

Decide which of these are really objects which the

project requires and organize them in related

clusters

50

Grammatical ParsingUniversity Bank will be opening in Oxford, Mississippi, in January,

2000. We plan to use a full service automated teller machine (ATM)

system.The ATM system will interact with the customer through a

display screen, numeric and special input keys, a bankcard reader, a

deposit slot, and a receipt printer.Customers may make deposits,

withdrawals, and balance inquires using the ATM machine, but the

update to accounts will be handled through an interface to the

Accounts system.Customers will be assigned a Personal Identification

Number (PIN) and clearance level by the Security system. The PIN can

be verified prior to any transaction.In the future, we would also like to

support routine operations such as a change of address or phone

number using the ATM

51

Grammatical Parsing University Bank will be opening in Oxford, Mississippi, in

January, 2000. We plan to use a full service automated teller machine (ATM) system.The ATM system will interact with the customer through a display screen, numeric and special input keys, a bankcard reader, a deposit slot, and a receipt printer.Customers may make deposits, withdrawals, and balance inquires using the ATM machine, but the update to accounts will be handled through an interface to the Accounts system.Customers will be assigned a Personal Identification Number (PIN) and clearance level by the Security system. The PIN can be verified prior to any transaction.In the future, we would also like to support routine operations such as a change of address or phone number using the ATM

52

Typical Classes (a reminder) External entities - printer, user, sensor Things - reports, displays, signals Occurrences or events (e.g., interrupt, alarm) Roles (e.g., manager, engineer, salesperson) Organizational units (e.g., division, team) Places (e.g., manufacturing floor or loading dock) Structures (e.g., sensors, four-wheeled vehicles, or computers)

But, how do we select classes?

53

Selecting Classes—Criteria

needed servicesneeded services

multiple attributesmultiple attributes

common attributescommon attributes

common operationscommon operations

essential requirementsessential requirements

retained informationretained information

54

CRC Modeling

See specific CRC slides

55

Rules of Thumb The model should focus on requirements that are visible

within the problem or business domain. The level of abstraction should be relatively high.

Each element of the analysis model should add to an overall understanding of software requirements and provide insight into the information domain, function and behavior of the system.

Delay consideration of infrastructure and other non-functional models until design.

Minimize coupling throughout the system. Be certain that the analysis model provides value to all

stakeholders. Keep the model as simple as it can be.

56

Writing the Software Specification

Everyone knew exactly what had to be done until someone wrote it down!

57

Specification Guidelinesuse a layered format that provides increasing detail as the "layers" deepen

use consistent graphical notation and apply textual terms consistently (stay away from aliases)

be sure to define all acronyms

be sure to include a table of contents; ideally, include an index and/or a glossary

write in a simple, unambiguous style (see "editing suggestions" on the following pages)

always put yourself in the reader's position, "Would I be able to understand this if I wasn't intimately familiar with the system?"

58

Specification GuidelinesBe on the lookout for persuasive connectors, ask why? keys: certainly, therefore, clearly, obviously, it follows that ...

Watch out for vague terms keys: some, sometimes, often, usually,ordinarily, most, mostly ...

When lists are given, but not completed, be sure all items are understood keys: etc., and so forth, and so on, such as

Be sure stated ranges don't contain unstated assumptions e.g., Valid codes range from 10 to 100. Integer? Real? Hex?

Beware of vague verbs such as handled, rejected, processed, ...

Beware "passive voice" statements e.g., The parameters are initialized. By what?

Beware "dangling" pronouns e.g., The I/O module communicated with the data validation module and its contol flag is set. Whose control flag?

59

Specification GuidelinesWhen a term is explicitly defined in one place, try

substituting the definition forother occurrences of the term

When a structure is described in words, draw a picture

When a structure is described with a picture, try to redraw the picture to emphasize different elements of the structure

When symbolic equations are used, try expressing their meaning in words

When a calculation is specified, work at least two examples

Look for statements that imply certainty, then ask for proof keys; always, every, all, none, never

Search behind certainty statements—be sure restrictions or limitations are realistic