CSC
450
CSC450
Software Engineering
Devon M. Simmonds
University of North Carolina, Wilmington
Introduction to System
Engineering
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Outline
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CSC
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Introduction to system engineering
System engineering tasks
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Need identification and scoping
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Information gathering techniques
Workflow modeling with UML activity diagrams
Feasibility studies
Function/need allocation
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System Engineering/Analysis
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Software Lifecycle Activities
Software Design
Requirements Analysis
Implementation
System Engineering
Testing
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Systems Engineering
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Deployment
Identify needs/problems
Allocation of roles
Hardware
Procedures
Software
Evolution
Feasibility studies
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What is a System?
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A system may be defined as a collection of
interacting, interdependent components
which act together in achieving some
common goal.
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Each component may itself be a system.
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What is a System?
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A business/computer-based system is
usually composed of the following:
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Software
Hardware
People
Documentation
Procedures
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System Engineering
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Software exists within some larger
system
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Encompassing system must be
understood if software is to work
properly within system
The domain is the general field of
business or technology in which
the clients will use the software
Domain analysis : the process by
which a software engineer learns
about the domain to better
understand the problem:
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A domain expert is a person who
has a deep knowledge of the
domain
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Aviation System
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What does it consist of?
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System
Engineering (2)
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Always design a thing by considering it in its
next larger context – a chair in a room, a
room in a house, a house in an environment,
an environment in a city plan.”
If the system exists within a business organization
system engineering is referred to as business
process engineering
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Systems engineering is also called systems
analysis.
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System Engineering/AnalysisCSC
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Process
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Systems engineering is a problem-solving activity concerned
with modeling the system encompassing software.
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System engineering process
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Establishing the user’s need and the software scope
Conducting software project planning
Conducting a feasibility study
Allocating functions to hardware, software, people,
database, etc.
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System
Engineering/Analysis
Tasks
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Need identification and scoping
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Project planning
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Feasibility study
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Allocation of functions/needs to components
Hardware
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Software
Allocating
functions to software includes scoping!
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Procedures
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System
Engineering/Analysis:
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Need identification process
Information
One onGathering
One
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Group meeting
The need identification process involves:
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Initial meetings
Information gathering
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Document reviews, interviews, questionnaires, observations,
measurements
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System
Analysis:
Need identification
process
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The need identification process involves:
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Initial meetings
Information gathering (Kendall & Kendall)
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Document reviews, interviews, questionnaires, observations,
measurements
Workflow modeling & analysis
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Activity diagrams/dataflow diagrams using UML
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Information Gathering
Techniques
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Information Gathering:
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Document Reviews
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Why review documents anyway?
Often a useful point to start in the analysis process
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Advantages of document review:
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Documentation is generally portable
Documentation is generally easily accessible
Disadvantages:
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Documentation typically available on various aspect of an organization
The volume of documentation may be large
Documentation is often inaccurate and outdated
Documentation is often sketchy.
Checklist of potential documents:
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Manuals detailing company organization, policy and existing systems.
Manuals detailing job descriptions and staff duties and responsibilities.
Previous reports and investigations.
Publicity and promotional material.
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Information Gathering:
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An interview is a directed conversation that is goaldriven and uses a question-answer format.
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Interviews
Exit interview, phone interview, lunch interview, panel
interview
Kinds of information sought
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Facts
Opinions
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Scenarios 1 conclusion?
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Owner is overstating the facts?
Scenarios 2 conclusion?
Interview Scenarios (from
Kendall
& Kendall)
Owner
is NOT overstating
the facts, she wants the problem with refunds
Scenario 2:
addressed!
Scenario 1:
Systems Engineer: “What are your major concerns related to customer refunds?”
Systems Engineer: “How many customer refunds do you typically give per week?”
Client: “Customer refunds are way too high. We need to get it right the first time”
Client: “About 20 to 25 per week”
Facts: When you search available documentation, the average is only 10.5 per
Facts:
week. When you search available documentation, the average is only 10.5 per week.
Question:
can
you
draw?
Question:What
Whatinferences
inferences
can
you
draw?
The interview is probably the single most important tool in information gathering process.
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Information Gathering:
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Interviews
Kinds of information sought
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Facts
Opinions
Feelings
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May reflect emotion, attitudes and
organizational culture
Goals
The interview is probably the single most important tool in information gathering process.
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Information Gathering:
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Interview Planning
Five preparatory steps
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Read background material
Establish interview objectives
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Decide who to interview
Prepare the interviewee
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Objectives address information sources, formats and
quality, decision-making, client goals
Call, send email, set limit of 45-60 mins
Decide on type of questions and structure of
questions
The interview is probably the single most important tool in information gathering process.
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Information Gathering:
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Interview Planning
Question types
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Open-ended
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Response not limited
Closed
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Limits response
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E.g. yes, no
Probes
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Follow-up questions
The interview is probably the single most important tool in information gathering process.
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Information Gathering:
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Interview Planning
Question pitfalls
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Avoid leading questions
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You agree with other managers that Sales should be
computerized, don’t you?
Do you think Sales should be computerized?
What do you think of computerizing sales?
Avoid double-barreled questions?
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Why are projects outsourced, and how did you go
about selecting the outsourcing process?
The interview is probably the single most important tool in information gathering process.
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Information Gathering:
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Interview Planning
Question formats – how to arrange
questions
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Pyramid structure
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Inductive style
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Funnel structure
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Deductive style
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closed questions  open-ended questions
Open-ended questions  closed questions
Diamond structure
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Combination of first two
Interviews may be recorded but be aware of the Hawthorne effect!
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CSC
Job Interview Questions - 450
Examples
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What are your long-range goals and objectives?
What are the most important rewards you expect in
your career?
What are your strengths, weaknesses, and interests?
Are you willing to travel?
How do you work under pressure?
Describe a situation in which you worked as part of a
team. What role did you take on? What went well
and what didn't?
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Information Gathering:
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Questionnaires
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A data gathering survey document with questions
and space for answers.
Similar rules apply for question design and
organization – with some differences
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Allow ample white space – attractiveness
Allow adequate space for responses
Use scales where possible
List most important questions first
Cluster items of similar content together
Bring up less controversial items first
Allocating functions to software includes scoping!
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Information Gathering:
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Questionnaires
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Scales
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Nominal
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Ordinal
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Used to order or rank
Interval
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Used to classify
Interval between items are equal
Ratio
Allocating functions to software includes scoping!
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Has an absolute zero
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Information Gathering:
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Questionnaires
Nominal Data
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Classification data
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1
2
3
4
=
=
=
=
Computer Science
Psychology
Accounting
Chemistry
no ordering, e.g. it makes no sense to state
that Psychology > Computer Science
arbitrary labels
Data can be counted but not ordered
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Information Gathering:
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Questionnaires
Ordinal Data
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Ordering but difference between values not
important
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1
2
3
4
5
=
=
=
=
=
Extremely Helpful
Very Helpful
Moderately Helpful
Not Very Helpful
Not Helpful At All
Data can be counted and ordered
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Information Gathering:
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Questionnaires
Interval Data
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Ordered, constant scale i.e. difference
between values are equal
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How many hours do dogs sleep at night?
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2
4
6
8
hours
hours
hours
hours
Data may be added and subtracted but not multiplied
or divided.
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Information Gathering:
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Questionnaires
Ratio Data
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Approximately how many hours do you
spend on the computer daily?
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0
2
4
6
8
Data may be added, subtracted, multiplied
and divided.
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Information Gathering:
Constructing Scales:
Validity &
reliability
Validity
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Does a question measure what it is
intended to measure?
Reliability
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Is the questionnaire consistent?
Allocating functions to software includes scoping!
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System Engineering Tasks
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Need identification and scoping
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Project planning
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Feasibility study
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Allocation of functions/needs to components
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Hardware
Software
Procedures
Allocating functions to software includes scoping!
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Feasibility Study
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A feasibility study is a
preliminary study undertaken
before the real work of a project
starts to ascertain the likelihood
of the project's success. It is an
analysis of possible alternative
solutions to a problem and a
recommendation on the best
alternative. Wikipedia.com
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Feasibility Study
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Feasibility study subareas
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Economic feasibility
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Technical feasibility
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Analysis of human and technical resources
Legal Feasibility
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Costs versus benefits
Analysis of legal constraints and issues
Alternatives
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Evaluation of alternative approaches to
solving problem.
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Feasibility Study
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Feasibility study subareas
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Economic feasibility
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Technical feasibility
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Are financial resources available?
Do cost/benefit analysis justify development?
Is the market ready for the product?
How difficult is it to build software?
Is required experience available?
Is required technology available?
Is time available to build software?
Legal Feasibility
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What legal problems do we anticipate?
Are these problems surmountable?
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Do we have legal counsel?
What are the cost implications of these problems?
A feasibility study is not complete without an analysis of risks?
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System Engineering Tasks
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Need identification and scoping
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Project planning
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Feasibility study
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Allocation of functions/needs to components
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Hardware
Software
Procedures
Allocating functions to software includes scoping!
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Need Identification:
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Workflow Modeling (later)
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Next, the role of modeling in
engineering software.
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Role of Models in Engineering
To help us understand complex systems
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Useful for both requirements and designs
Minimize risk by detecting errors and omissions early in the design cycle
(at low cost)
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Through analysis and experimentation
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Investigate and compare alternative solutions
To communicate understanding
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Stakeholders: clients, users, implementers, testers, documenters, etc.
To drive implementation
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The model as a blueprint for construction
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Engineering Models
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Engineering model:
A reduced representation of some system that
highlights the properties of interest from a given
viewpoint
Modeled system
Modeled
System
Functional System
Model
Functional
•We do not see everything at once
•We see a representation that is easily understood for the purpose at hand
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Models in other disciplines
New Hanover Regional Medical Center
First Floor Model
Doghouse
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How
models
help
Models
A model vary
is a representation
in
complexity
of an item
 Focus on what is important
A model does not show all the features
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Skyscraper
Essential complexity, accidental complexity
A model is an abstraction: abstraction = hide details
 Mitigate risks
 Ensure quality
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Models in other disciplines
2005 Champions
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A - Making a V-cut to get the
ball. B - Receiving Inside
Hand-off.
Roy Williams
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What characteristics should a useful
model possess?
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…
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Characteristics of Useful Models
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Abstract
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Understandable
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Faithfully represents the modeled system
Predictive
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Expressed in a form that is readily understood by observers
Accurate
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Emphasize important aspects while removing irrelevant ones
Can be used to answer questions about the modeled system
Inexpensive
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Much cheaper to construct and study than the modeled system
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The Remarkable Thing About
Software
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“Software has the rare property that
it allows us to directly evolve models
into full-fledged implementations
without changing the engineering
medium, tools, or methods!” - Bran Selic
• The model evolves into the system it models
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The Unified Modeling Language
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The UML is a standard diagramming language
to visualize the results of analysis and design.
UML is a tool
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Learning how to create high-quality models is not
equivalent to learning the UML
UML is simply a language for expressing models
The UML is not
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a process or methodology
an object-oriented analysis and design technique
a modeling technique
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UML Goals
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Define an easy-to-learn but semantically rich visual
modeling language
Unify the Booch, OMT, and Objectory modeling
languages
Include ideas from other modeling languages
Incorporate industry best practices
Address contemporary software development issues
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scale, distribution, concurrency, executability, etc.
Provide flexibility for applying different processes
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UML 2.* Diagram Types
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Class diagrams
Activity diagrams
State machines
Sequence diagrams
Object diagrams
Component diagrams
Deployment diagrams
Package diagrams
etc. 14 types altogether
LINK
UML Specification
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Need Identification:
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Workflow Modeling
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Workflow is a description of
work done, tasks performed, the
order in which tasks are
performed, who performs tasks,
how tasks are structured and
synchronized and the input and
output of activities.
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In UML, workflows may be described using
Activity Diagrams.
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Summary
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In this class we discussed
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What is system engineering
System engineering tasks

Need identification and scoping





Information gathering techniques
Workflow modeling with UML activity diagrams
Feasibility studies
Function/need allocation
Brief overview of UML
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Summary
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What’s coming next class?
Qu es
ti ons?
______________________
Devon M. Simmonds
Computer Science Department
University of North Carolina Wilmington
_____________________________________________________________
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