Illinois Institute of Technology
CS487
Software Engineering
Requirements II- part B
Instructor David Lash
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Example of Modality and
Cardinality
Cardinality: A
single customer
has order(s)
Customer
Cardinality:
Multiple orders for
a customer.
1
Modality: An
order must have a
customer
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has
M
Orders
Modality: A
customer does not
require an order
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
Control Panel
HomeOwner
Monitoring
Service
Security System
Sensor
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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
Sensor needs security
system
Security System
Security System needs
sensor.
Enables/
disables
Sensor
Sensor controled from
Security system controls 1
single security system
or more sensors
monitors
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High-Level Modeling Tools

System Modeling
–
–

Data Modeling
–

Entity-Relation - Data objects and their
relationships
Information flow diagrams
–

System Context Diagram
Partitioning
Data flow diagrams - how data
transforms in system- how functions
transform data
Control Specifications
–
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State diagrams - how system behaves
as result of external events .
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)
dividend
quotient
integer
division
remainder
divisor
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)
External
Data Store (all
or part of the
information
store)
Thing
System
External
Thing
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External
Thing
Data Flow Diagram
(Data Flows or Connectors)
street address
city
address
state
ZIP Code
number
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Level 0 Data Flow
External
Entity
1
an
Tr
Inp
ut D
ata
System
External
Entity
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ta
a
ut D
Inp
Input Data
Output
data
Ou
tpu
tD
ata
External
Entity
External
Entity
External
Entity
Level 0 Data Flow
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Level 0 Data Flow
(Interactive System)
A generalization of users
External
Entity
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Manual
Input
System
Generated
Output
Data Flow Diagram
(Divide Operation)
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Level 1 - Data Flow
(Major Process Operators)
Extern
IN1
In Stru 1
Process 1
In Stru 1-A
Data Stru 1
DATA
STORE
Data Stru 1
Proces4
Process 2
Rpt Stru 2
External
OUT2
Tran 1
Data Stru 1
Process3
External
IN2
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In Stru 2
External
OUT1
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)
Fill in Data
IN Stru 1
Complete
missing data
Process 3c
Process 3b
IN Stru 1
Complete
IN Stru 1
missing data
IN Stru 1
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Stru Data
Process 3a
DATA Store
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 2
(B1 & NOT T1): No action.
(B1 & T1): Invoke state2
B2: Invoke state0
State 0
B2: Invoke state 1
State 1
T1: Set Time to nn
States:
State 0: Normally idle
State 1: Processing
State 2: The blue screen of death
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Events:
T1 - Time 1
B1 - Button 1
B2 - Button 2
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.
(Event & Condition):
Data
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State
Name
Action(s)
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
SP: Read Next,
Set Error
Read Next
CR: Read Next
New Line
CR: Read Next
Store Word
SP: Read Next
Store Word
SP: Read Next,
Set Error
Space
Char: Read Next
CR: Read Next
Char: Read Next
Word
EOF: List Stored Words
EOF: List Stored Words
EOF: List Stored Words
EOF
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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
–
–

Data Modeling
–

Entity-Relation - Data objects and their
relationships
Information flow diagrams
–

System Context Diagram
Partitioning
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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