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Illinois Institute of Technology

CS487

Software Engineering

Requirements II- part B

Instructor David Lash

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Example of Modality and Cardinality

Customer has Orders

M odality: Anorder must have acustomer

M odality: Acustomer does notrequire an order

Card ina lity: Asing le customerhas order(s)

Card ina lity:M ultip le orders fora customer.

1 M

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Example of ERD

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Creating ERDs Take each “things” (e.g., car, contact list)

mentioned in requirements and ask about relationships to other things

Object-relationship pairs and therefore identified

– Explore the carinality and modality of that relationship

Repeat for each object identified Review the objects and establish

attributes Form the ERD and review

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ERD II example - Homesafe Enables homeowner (HW) to config

security system (SS), during install HS monitors all sensors connected to SS HS interacts with HW via Keypad on cntl

panel (CP) CP is used to program system Each sensor (SEN) is assigned a # and

type A master passwd is programmed, Tel

number are input for dialing on Sensor event (SEN)

on SEN event, alarm invoked & SS dials phone number, and gives info to (MS) monitoring Service

CP has keyboard input stuff

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ERD II example - Homesafe

Sensor

Security System

HomeOwner

MonitoringService

Control Panel

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ERD II example - Derived Relationships

SS monitors sensor SS enables/disables sensor SS tests sensor SS program sensor

Attributes of Sensor has type, internal id, zone location, alarm level

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ERD II example - Homesafe

programs

Enables/disables

monitors

SensorSecurity System

Security system controls 1or more sensors

Security System needssensor.

Sensor controled fromsingle security system

Sensor needs securitysystem

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High-Level Modeling Tools System Modeling

– System Context Diagram– Partitioning

Data Modeling – Entity-Relation - Data objects and their

relationships Information flow diagrams

– Data flow diagrams - how data transforms in system- how functions transform data

Control Specifications– State diagrams - how system behaves

as result of external events .

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Data Flow Diagrams ( Information Flow )

A graphical technique that depicts information flow and the transforms that are applied as data moves from input to output.

– Input can be sensor, human operator, web page input, hardware

– Transformation can be logical comparison, numerical algorithm, graphic algorithm,

– Output can be LED, web page, report, effect on hardware

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Data Flow Diagram (Divide Operation)

in tege rd iv is ion

d iv idend

d iv iso rrem a inde r

quo tien t

Level 0 DF (fundamental) diagram represents system with 1 bubble

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Data Flow Diagram(Symbols)

Process (Data Transformation)

External Entity (I/O Src/Dest)

Data Store (all or part of the information store)

System

External

Thing

External

Thing

External

Thing

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Data Flow Diagram (Data Flows or Connectors)

address

s tree t add ress

c ity

s ta te

Z IP C ode

num ber

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Level 0 Data Flow

E xte rna lE n tity

E xte rna lE n tity

S ys tem

E xte rna lE n tity

E xte rna lE n tity

E xte rna lE n tity

Output dataInput Data

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Level 0 Data Flow

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Level 0 Data Flow (Interactive System)

E xte rna lE n tity

S ys tem

M anua lInpu t

G enera tedO utpu t

A generalization of users

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Data Flow Diagram (Divide Operation)

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Level 1 - Data Flow (Major Process Operators)

E xte rnIN 1

E xte rna lIN 2

P rocess3

P rocess 1

D A TAS TO R E

P rocess 2

E xte rna lO U T1

P roces4

In Stru 1 In Stru 1-A

Data Stru 1

Data Stru 1

Data Stru 1

E xte rna lO U T2

In Stru 2

Rpt Stru 2

Tran 1

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Guidelines for building a Data Flow Diagram

1. Show the first level (level 0) as a single process with all of its external inputs and outputs sources.

2. Primary input and output should be carefully noted.

3. Refinement begins by isolating candidate processes.

4. All data flows and symbols should be labeled with meaningful names.

5. Information flow continuity must be maintained. (within the refinement)

6. One bubble at a time is expanded.

7. Record all components in the data dictionary.

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Level N Data Flow (Detailed Process to Transform)

Process 3a

Process 3b

Process 3c

D A TA S to reIN Stru 1

IN Stru 1Com plete

IN Stru 1Com plete

Stru Data

IN Stru 1m issing data

F ill in D a ta

m issing data

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Data-Flow Example

R.S. Pressman, Ph.D. Software Engineering: A Practitioner’s Approach. McGraw-Hill, New York, New York. 1997. p. 377

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Level 1 - introduce process and data store

R.S. Pressman, Ph.D. Software Engineering: A Practitioner’s Approach. McGraw-Hill, New York, New York. 1997. p. 378

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Level 2 - Show more detail for each level 1 process (monitor sensors)

R.S. Pressman, Ph.D. Software Engineering: A Practitioner’s Approach. McGraw-Hill, New York, New York. 1997. p. 379

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Behavioral Modeling

Behavior is the observable effects of an event,

including its results.

Control flow diagramming – An extension to data flow diagramming

– Adds events to the data model

State transition diagrams– More traditional behavior model.

– Useful for a variety of applications.

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State Diagram

A state diagram illustrates how the system moves from state to state. For example

– monitoring state -> alarm state -> monitoring state (homesafe)

– What events trigger the change in state? Sense danger, reset alarm

A state diagram shows the state machine – State Machine

A behavior that specifies the sequences of states an object goes through during its lifetime in response to events, together with its responses to those events

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What is the scientific base for state-machine?

Conservation of Momentum Law

When the resultant external force acting on a system is zero, the total momentum of the system remains constant.

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What are the components of a state machine?

States– Any observable mode of behavior.– A condition or situation during the life of an

object during which it satisfies some condition, performs some activity or waits for some event.

– Description is contained in a data dictionary.

Name

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What are the components of a state machine?

Transitions– A relationship between two states indicating

that an object in the first state will perform certain actions and enter the second state when a specified event occurs and specified conditions are satisfied.

(Event & Conditions)

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Types of state transition diagrams

Action on transition– Actions are performed on event transition– On the diagram that is where the actions are

defined.– Events, Conditions and Actions are described

in the data dictionary.

(Event & Conditions): Action(s)

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Example of action on transition

State 0

State 1

State 2

Events:T1 - T im e 1B1 - Button 1B2 - Button 2

T1: Set T im e to nn

(B1 & T1): Invoke state2

(B1 & NOT T1): No action.

B2: Invoke state0

B2: Invoke state 1

States:State 0: Norm ally idleState 1: ProcessingState 2: The blue screen of death

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Types of state-transition diagrams.

Action on state entry– Actions are performed when a state is entered.– Transitions carry optional data and not actions.– States, events, conditions and data are

described in the data dictionary.

State Name

Action(s)(Event & Condition): Data

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Parser Example

Given a text (stored on a file) consisting of words separated by SPACE characters or by CR (new line) characters, a program is supposed to read the text and suppress all extra SPACE characters according to the following rules:

– Words should be separated only by one

SPACE character, – Between a word and CR character there

should be no SPACE character,– New line cannot start with a SPACE character,– Program terminates on EOF (End of File)

character.

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Example

Processing States

– New Line. Last character was a CR or

beginning of process.

– Word. Last character is not a space or CR.

– Space. Last character is a space.

– End-of-file.

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Example

Events (must be account for in each state)

– End-of-file indicator

– NL Character

– Space Character

– Text Characters

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Example

Actions

– Read Next

– Store Word

– Set Error

– List Stored Words

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State Diagram Example

New Line

SP: Read Next, Set Error

EO F

Space

W ordCR: Read Next

Char: Read Next

EO F: L ist S tored W ords

SP: Read Next S tore W ord

EO F: L ist S tored W ords EO F: L ist S tored W ords

CR: Read Next S tore W ord

Char: Read Next

CR: Read Next

SP: Read Next, Set ErrorRead Next

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Analysis Modeling Software models must represent:

– the information that the sftwr acts on– the function that enable action – and overall system behavior

Requirements Models Roles: – Understand the information, function, behavior

and information in the system– Focal Point for the review - Avoids lots of wrds

help deal with complexity of problem– Become foundation for design process

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High-Level Modeling Tools System Modeling

– System Context Diagram– Partitioning

Data Modeling – Entity-Relation - Data objects and their

relationships Information flow diagrams

– Data flow diagrams - how data transforms in system- how functions transform data

Control Specifications– State diagrams - how system behaves

as result of external events.