System Engineering
based on
Chapter 6 - Software Engineering: A Practitioner’s Approach, 6/e
copyright © 1996, 2001, 2005
R.S. Pressman & Associates, Inc.
For University Use Only
May be reproduced ONLY for student use at the university level
when used in conjunction with Software Engineering: A Practitioner's Approach.
Any other reproduction or use is expressly prohibited.
1
Waterfall model 1 [aka Royce1970]
Systems Engineering
Software Req. Analysis
Operation/Maintenance
Project Planning
Design
Implementation
Testing/Verification
Release
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System Engineering
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Elements of a computer-based system
 Software
 Hardware
 People
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Database
Documentation
Procedures
Systems
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A hierarchy of macro-elements
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Business Process (Re-)Engineering
to identify how information systems can best meet the
strategic goals of an enterprise, using an integrated set of procedures,
methods, and tools, given a set of business rules and constraints.
focuses first on the enterprise and then on the business area
creates enterprise models, data models and process models
(processes/services and interrelationships of processes and data)
creates a framework for better information management,
distribution, and control
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System Architectures
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Three different architectures must be analyzed and designed within the
context of business objectives and goals:
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data architecture provides a framework for the information needs of a
business or business function (e.g., incident location, patient status,
ambulance location, drivers’ lunch hours and break, hospital locations, etc.)
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application architecture encompasses those elements of a system that
transform objects within the data architecture for some business purpose
(e.g., determine ambulance availability, determine hospital availability, etc.)
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technology infrastructure provides the foundation for the data and application
architectures (e.g., communication lines, computer platforms, etc.)
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System Modeling with UML
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Deployment diagrams
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Activity diagrams
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Each 3-D box depicts a hardware element that is part of the
physical architecture of the system
Represent procedural aspects of a system element
Class diagrams
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Represent system level elements in terms of the data that describe
the element and the operations that manipulate the data
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Skip – Self Reading
Possibly One Lecture on UML
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Conveyor Line Sorting System (CLSS)
CLSS must be developed such that boxes moving along a conveyor line will
be identified and sorted into one of six bins at the end of the line. The
boxes will pass by a sorting station where they will be identified. Based
on an identification number printed on the side of the box and a bar
code, the boxes will be shunted into the appropriate bins. Boxes pass in
random order and are evenly spaced. The line is moving slowly.
A desk-top computer located at the sorting station executes all CLSS
software, interacts with the bar-code reader to read part numbers on
each box, interacts with the conveyor line monitoring equipment to
acquire conveyor line speed, stores all part numbers sorted, interacts
with a sorting station operator to produce a variety of reports and
diagnostics, sends control signals to the shunting hardware to sort the
boxes, and communicates with a central factory automation system. 8
Deployment Diagram
CLSS processor
Operat or display
Sort ing subsyst em
Sensor dat a
acquisit ion subsyst em
Conveyor
Pulse t ach
shunt cont roller
Bar code reader
Shunt act uat or
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Activity Diagram
st a rt c o n v e y o r l i n e
g e t c o n v e y o r sp e e d
re a d b a r c o d e
v alid bar c ode
inv alid bar c ode
det er m ine bin loc at ion
se t f o r re j e c t b i n
se n d sh u n t
c o n t ro l d a t a
g e t sh u n t st a t u s
g e t c o n v e y o r st a t u s
re a d b a r c o d e
p ro d u c e re p o rt e n t ry
c onv ey or s t opped
c onv ey or in m ot ion
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Class Diagram
class name
Box
barcode
forwardSpeed
conveyorLocat ion
height
widt h
dept h
weight
cont ent s
readBarcode( )
updat eSpeed ( )
readSpeed( )
updat eLocat ion( )
readLocat ion( )
get Dimensions( )
get Weight( )
checkCont ent s( )
at t ribut es
not e use of capit al
let t er f or mult i-word
at t ribut e names
operat ions
( parent heses at end
of name indicat e t he
list of at t ribut es t hat t he
operat ion requires)
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Requirements Engineering
based on
Chapter 7 - Software Engineering: A Practitioner’s Approach, 6/e
copyright © 1996, 2001, 2005
R.S. Pressman & Associates, Inc.
For University Use Only
May be reproduced ONLY for student use at the university level
when used in conjunction with Software Engineering: A Practitioner's Approach.
Any other reproduction or use is expressly prohibited.
12
Requirements Engineering Process:
A Basic Framework [Loucopolos]
Many variations and extensions
3 fundamental activities:
understand, (formally) describe, attain an agreement on, the problem

User reqs
User
User feedback
knowledge
Elicitation
Req. models
Specification
For more knowledge
Val. result
Validation
Domain knowledge
Domain knowledge
Problem
Domain
(domain experts, laws, standards, policies, documents, etc.)
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Elicitation: determine what’s really needed, why needed, whom to talk to
Specification: produce a (formal) RS model: translate "vague" into "concrete", etc. make various decisions
on what & how
Validation: assure that the RS model satisfies the users’ needs
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Requirements Engineering
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Elicitation - Inception—ask a set of questions that establish …
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Specification — can be any one (or more) of the following:
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(basic) understanding of the problem
the people who want a solution
the nature of the solution that is desired, and
the effectiveness of preliminary communication and collaboration between the
customer and the developer
A written document
A set of models - A formal mathematical?
A collection of user scenarios (use-cases)
A prototype
Validation — a review mechanism that looks for
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errors in content or interpretation
areas where clarification may be required
missing information
inconsistencies (a major problem when large products or systems are engineered)
conflicting or unrealistic (unachievable) requirements.
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Eliciting Requirements - Inception

Identify (key) stakeholders
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These are the people who will be involved in the negotiation
“who else do you think I should talk to?”
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Recognize multiple points of view
Work toward collaboration
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The first questions
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Who is behind the request for this work?
Who will use the solution?
What will be the (economic) benefit of a successful solution
Is there another source for the solution that you need?
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Eliciting Requirements
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meetings are conducted and attended by both software engineers and customers
rules for preparation and participation are established
an agenda is suggested
a "facilitator" (can be a customer, a developer, or an outsider) controls the meeting
a "definition mechanism" (can be work sheets, flip charts, or wall stickers or an
electronic bulletin board, chat room or virtual forum) is used
the goal is
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to identify the problem
propose elements of the solution
negotiate different approaches, and
specify a preliminary set of solution requirements
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Elicitation Work Products
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a statement of need, scope, and feasibility.
a list of customers, users, and other stakeholders who
participated in requirements elicitation
a description of the system’s technical environment (cf.
enterprise model in system engineering).
a list of requirements (preferably organized by function)
and the domain constraints that apply to each.
a set of usage scenarios that provide insight into the use of
the system or product under different operating conditions.
any prototypes developed to better define requirements.
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Building the Analysis Model
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Elements of the analysis model
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Scenario-based elements
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Class-based elements
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Implied by scenarios
Behavioral elements
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Functional—processing narratives for software functions
Use-case—descriptions of the interaction between an
“actor” and the system
State diagram
Flow-oriented elements
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Data flow diagram
18
Skip – Self Reading
Possibly One Lecture on UML
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Use-Cases

A collection of user scenarios that describe the thread of usage of a system
Each scenario is described from the point-of-view of an “actor”—a person or
device that interacts with the software in some way
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Each scenario answers the following questions:
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Who is the primary actor, the secondary actor (s)?
What are the actor’s goals?
What preconditions should exist before the story begins?
What main tasks or functions are performed by the actor?
What extensions might be considered as the story is described?
What variations in the actor’s interaction are possible?
What system information will the actor acquire, produce, or change?
Will the actor have to inform the system about changes in the external
environment?
What information does the actor desire from the system?
Does the actor wish to be informed about unexpected changes?
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Use-Case Diagram
Arms/ disarms
syst em
Accesses syst em
via Int ernet
sensors
homeow ner
Responds t o
alarm event
Encount ers an
error condit ion
syst em
administ rat or
Reconf igures sensors
and relat ed
syst em f eat ures
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Class Diagram
From the SafeHome system …
Sensor
name/id
type
location
area
characteristics
identify()
enable()
disable()
reconfigure ()
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State Diagram
Reading
commands
Init ializat ion
t urn copier
“on“
syst em st at us=“not ready”
display msg = “please wait ”
display st at us = blinking
subsyst ems
ready
ent ry/ swit ch machine on
do: run diagnost ics
do: init iat e all subsyst ems
not jammed
syst em st at us=“Ready”
display msg = “ent er cmd”
display st at us = st eady
paper f ull
ent ry/ subsyst ems ready
do: poll user input panel
do: read user input
do: int erpret user input
t urn copier “of f ”
st art copies
Making copies
copies complet e
syst em st at us=“Copying”
display msg= “copy count =”
display message=#copies
display st at us= st eady
ent ry/ st art copies
do: manage copying
do: monit or paper t ray
do: monit or paper f low
paper t ray empt y
paper jammed
problem diagnosis
syst em st at us=“Jammed”
display msg = “paper jam”
display message=locat ion
display st at us= blinking
ent ry/ paper jammed
do: det ermine locat ion
do: provide correct ivemsg.
do: int errupt making copies
load paper
syst em st at us=“load paper”
display msg= “load paper”
display st at us= blinking
ent ry/ paper empt y
do: lower paper t ray
do: monit or f ill swit ch
do: raise paper t ray
not jammed
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Validating Requirements
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Is each requirement consistent with the overall objective for the system/product?
Have all requirements been specified at the proper level of abstraction? That is, do
some requirements provide a level of technical detail that is inappropriate at this
stage?
Is the requirement really necessary or does it represent an add-on feature that may
not be essential to the objective of the system?
Is each requirement bounded and unambiguous?
Does each requirement have attribution? That is, is a source (generally, a specific
individual) noted for each requirement?
Do any requirements conflict with other requirements?
Is each requirement achievable in the technical environment that will house
the system or product?
Is each requirement testable, once implemented?
Does the requirements model properly reflect the information, function and
behavior of the system to be built.
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