CSC450 Software Engineering

CSC450CSC450

1

Devon M. SimmondsUniversity of North Carolina,

Wilmington

CSC450Software

Engineering

Introduction to System Engineering

CSC450CSC450

2

Outline Introduction to system engineering System engineering tasks

Need identification and scoping Information gathering techniques Workflow modeling with UML activity

diagrams Feasibility studies Function/need allocation

CSC450CSC450

3

System Engineering/Analysis

Software Lifecycle Activities

System Engineering

Requirements AnalysisSoftware Design

Implementation

Testing

Deployment

Evolution

Systems Engineering Identify needs/problems Allocation of roles

Hardware Procedures Software

Feasibility studies

CSC450CSC450

4

What is a System?

A system may be defined as a collection of interacting, interdependent components which act together in achieving some common goal. Each component may itself be a system.

CSC450CSC450

5

What is a System?

A business/computer-based system is usually composed of the following: Software Hardware People Documentation Procedures

CSC450CSC450

6

System Engineering Software exists within some

larger system 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: A domain expert is a person

who has a deep knowledge of the domain

Aviation System What does it consist of?

CSC450CSC450

7

System Engineering (2)

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

Systems engineering is also called systems analysis.

CSC450CSC450

8

System Engineering/Analysis Process

Systems engineering is a problem-solving activity concerned with modeling the system encompassing software. System engineering process

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.

CSC450CSC450

9

System Engineering/Analysis Tasks

Need identification and scoping

Project planning Feasibility study Allocation of functions/needs to components

Hardware Software ProceduresAllocating functions to software includes scoping!

CSC450CSC450

10

System Engineering/Analysis: Need identification process

The need identification process involves: Initial meetings Information gathering

Document reviews, interviews, questionnaires, observations, measurements

Group meetingOne on One

Information Gathering

CSC450CSC450

11

The need identification process involves: Initial meetings Information gathering (Kendall & Kendall)

Document reviews, interviews, questionnaires, observations, measurements

Workflow modeling & analysis Activity diagrams/dataflow diagrams using UML

System Analysis: Need identification process

CSC450CSC450

Information Gathering Techniques

12

CSC450CSC450

13

Information Gathering: Document Reviews

Why review documents anyway? Often a useful point to start in the analysis process

Documentation typically available on various aspect of an organization

Advantages of document review: Documentation is generally portable Documentation is generally easily accessible

Disadvantages: The volume of documentation may be large Documentation is often inaccurate and outdated Documentation is often sketchy.

Checklist of potential documents: 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.

CSC450CSC450

14

Information Gathering: Interviews An interview is a directed conversation that is

goal-driven and uses a question-answer format. Exit interview, phone interview, lunch interview,

panel interview Kinds of information sought

Facts Opinions

Scenarios 1 conclusion? Owner is overstating the facts?

Scenarios 2 conclusion? Owner is NOT overstating the facts, she wants the problem with

refunds addressed!

The interview is probably the single most important tool in information gathering process.

Interview Scenarios (from Kendall & Kendall)Scenario 1:Systems Engineer: “How many customer refunds do you typically give per week?”Client: “About 20 to 25 per week”Facts: When you search available documentation, the average is only 10.5 per week.Question: What inferences can you draw?

Scenario 2:Systems Engineer: “What are your major concerns related to customer refunds?”Client: “Customer refunds are way too high. We need to get it right the first time”Facts: When you search available documentation, the average is only 10.5 per week.Question: What inferences can you draw?

CSC450CSC450

15

Information Gathering: Interviews Kinds of information sought

Facts Opinions Feelings

May reflect emotion, attitudes and organizational culture

Goals


CSC450CSC450

16

Information Gathering: Interview Planning

Five preparatory steps Read background material Establish interview objectives

Objectives address information sources, formats and quality, decision-making, client goals

Decide who to interview Prepare the interviewee

Call, send email, set limit of 45-60 mins Decide on type of questions and structure

of questions


CSC450CSC450

17


Question types Open-ended

Response not limited Closed

Limits response E.g. yes, no

Probes Follow-up questions


CSC450CSC450

18


Question pitfalls Avoid leading questions

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? Why are projects outsourced, and how did you

go about selecting the outsourcing process?


CSC450CSC450

19


Question formats – how to arrange questions Pyramid structure

Inductive style closed questions open-ended questions

Funnel structure Deductive style

Open-ended questions closed questions Diamond structure

Combination of first two

Interviews may be recorded but be aware of the Hawthorne effect!

CSC450CSC450

20

Job Interview Questions - Examples 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?

CSC450CSC450

21

Information Gathering:Questionnaires

A data gathering survey document with questions and space for answers.

Similar rules apply for question design and organization – with some differences 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!

CSC450CSC450

22


Scales Nominal

Used to classify Ordinal

Used to order or rank Interval

Interval between items are equal Ratio

Has an absolute zeroAllocating functions to software includes scoping!

CSC450CSC450

23


Nominal Data Classification data

1 = Computer Science 2 = Psychology 3 = Accounting 4 = Chemistry

no ordering, e.g. it makes no sense to state that Psychology > Computer Science

arbitrary labels Data can be counted but not ordered

CSC450CSC450

24


Ordinal Data Ordering but difference between values

not important 1 = Extremely Helpful 2 = Very Helpful 3 = Moderately Helpful 4 = Not Very Helpful 5 = Not Helpful At All

Data can be counted and ordered

CSC450CSC450

25


Interval Data Ordered, constant scale i.e. difference

between values are equal How many hours do dogs sleep at night?

2 hours 4 hours 6 hours 8 hours

Data may be added and subtracted but not multiplied or divided.

CSC450CSC450

26


Ratio Data Approximately how many hours do

you spend on the computer daily? 0 2 4 6 8 Data may be added, subtracted,

multiplied and divided.

CSC450CSC450

27

Information Gathering:Constructing Scales: Validity & reliability

Validity Does a question measure what it is

intended to measure? Reliability

Is the questionnaire consistent?Allocating functions to software includes scoping!

CSC450CSC450

28

System Engineering Tasks

Need identification and scoping Project planning

Feasibility study Allocation of functions/needs to components

Hardware Software Procedures


CSC450CSC450

29

Feasibility Study 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

CSC450CSC450

30

Feasibility Study Feasibility study subareas

Economic feasibility Costs versus benefits

Technical feasibility Analysis of human and technical

resources Legal Feasibility

Analysis of legal constraints and issues Alternatives

Evaluation of alternative approaches to solving problem.

CSC450CSC450

31

Feasibility Study Feasibility study

subareas Economic feasibility

Are financial resources available? Do cost/benefit analysis justify development? Is the market ready for the product?

Technical feasibility How difficult is it to build software? Is required experience available? Is required technology available? Is time available to build software?

Legal Feasibility What legal problems do we anticipate? Are these problems surmountable?

Do we have legal counsel? What are the cost implications of these problems?

A feasibility study is not complete without an analysis of risks?

CSC450CSC450

32

System Engineering Tasks

Need identification and scoping Project planning

Feasibility study

Allocation of functions/needs to components Hardware Software Procedures


CSC450CSC450

33

Need Identification: Workflow Modeling (later)

Next, the role of modeling in engineering software.

CSC450CSC450

34

Role of Models in Engineering

To help us understand complex systems Useful for both requirements and designs

Minimize risk by detecting errors and omissions early in the design cycle (at low cost)

Through analysis and experimentation Investigate and compare alternative solutions

To communicate understanding Stakeholders: clients, users, implementers, testers,

documenters, etc. To drive implementation

The model as a blueprint for construction

CSC450CSC450

35

Engineering Models Engineering model:

A reduced representation of some system that highlights the properties of interest from a given viewpoint

Functional ModelModeled systemModeled System Functional System

• We do not see everything at once• We see a representation that is easily understood for the purpose at hand

CSC450CSC450

36

Models in other disciplines

New Hanover Regional Medical Center First Floor Model

A model is a representation of an item A model does not show all the features A model is an abstraction: abstraction = hide details

How models help Focus on what is important

Essential complexity, accidental complexity Mitigate risks Ensure quality

Doghouse Skyscraper Models vary in

complexity

CSC450CSC450

37

Models in other disciplines

A - Making a V-cut to get the ball. B - Receiving Inside Hand-off.

Roy Williams

2005 Champions

CSC450CSC450

38

What characteristics should a useful model possess?

…

CSC450CSC450

39

Characteristics of Useful Models

Abstract Emphasize important aspects while removing irrelevant

ones Understandable

Expressed in a form that is readily understood by observers

Accurate Faithfully represents the modeled system

Predictive Can be used to answer questions about the modeled

system Inexpensive

Much cheaper to construct and study than the modeled system

CSC450CSC450

40

The Remarkable Thing About Software

“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

CSC450CSC450

41

The Unified Modeling Language

The UML is a standard diagramming language to visualize the results of analysis and design.

UML is a tool 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

a process or methodology an object-oriented analysis and design technique a modeling technique

http://www.omg.org/uml/

CSC450CSC450

42

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 scale, distribution, concurrency, executability, etc.

Provide flexibility for applying different processes

UML Goals

CSC450CSC450

43

Class diagrams Activity diagrams State machines Sequence diagrams Object diagrams Component diagrams Deployment diagrams Package diagrams etc. 14 types altogether

UML 2.* Diagram Types

UML SpecificationLINK

http://www.omg.org/cgi-bin/apps/doc?formal/07-02-05.pdf

http://www.omg.org/cgi-bin/apps/doc?formal/07-02-05.pdf

CSC450CSC450

44

Need Identification: Workflow Modeling

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. In UML, workflows may be described

using Activity Diagrams.

CSC450CSC450

45

Summary In this class we discussed

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

CSC450CSC450

46

Summary What’s coming next class?

______________________Devon M. Simmonds

Computer Science DepartmentUniversity of North Carolina Wilmington

_____________________________________________________________

Qu es ti ons?

Documents

CSC450 Software Engineering