Software Engineering. Introduction. Software Costs. Software is Expensive [Boehm] ... Columbus set sail for India. He ended up in the Bahamas...

(1)

Introduction

... Columbus set sail for India. He

ended up in the Bahamas ...

Software Engineering

The economies of ALL developed nations are dependent on software

More and more systems are software controlled Software engineering is concerned with theories,

methods and toolsfor professionalsoftware development

Software engineering expenditure represents a significant fraction of GNP in all developed countries

Software is Expensive [Boehm]

100 %

1965 1970 1985

Maintenance Development Hardware

Software Costs

Sofware development is human

intensive

There is no cost to produce a copy of a

given software

Software is flexible and can be changed

to adapt to user ever changing needs

(2)

Late Costly Unreliable

Many software projects are behind schedule

and have heavy cost overruns

An information system for a US company planned in 9 months and at a cost of

$250000; after 2.5 years and $2500000 the job was not done, it was estimated that another $3600000 would be needed [Mcfarlan].

An information system for a US company planned in 9 months and at a cost of

$250000; after 2. US Air Force command-and-control: contract $400000, renegotiated to $700000, to $2500000 final cost $3200000 [Boehm].

US defense survey: more than 70 % of all equipment failure were due to software. Failure of the Arianne 5 and an early Apollo flight were due to software failure, many

banks lost millions of dollars due to software inaccuracy.

Failure

Software failure are different from mechanical

or electrical system failure.

Mechanical systems develop some problem

(due to age) that did not exist earlier.

Software never wears out due to age. Errors are introduced during software

production.

When a software fails the

“bug”

was there

from the beginning

… may be in the environment ….

Software

Program: the author is the user (e.g., no

documentation or testing, no design).

Programming system product: used by

people other than the developer of the

system. This is

industrial software it

cost about 10 times

as much as a

corresponding program.

IEEE Software Definition

Software is the collection of computer programs,

procedures, rules and associated documentation and data.

Software means: industrial quality software.

(3)

Software Products

Generic products

• Stand-alone systems which are produced by a development

organization and sold on the open market to any customer

Most software expenditure is on generic

products but most development effort is

on bespoke systems

Bespoke (customized) products

• Systems which are commissioned by a specific customer and

developed specially by some contractor

Software product attributes

Maintainability

• It should be possible for the software to evolve to meet changing requirements

Dependability

• The software should not cause physical or economic damage in the event of failure

Efficiency

• The software should not make wasteful use of system resources

Usability

• Software should have an appropriate user interface and documentation

Importance of product characteristics

The relative importance of these

characteristics depends on the product and

the environment in which it is to be used

In some cases, some attributes may

dominate

• In safety-critical real-time systems, key attributes may be

dependability and efficiency

Costs tend to rise exponentially if very high

levels of any one attribute are required

Professional responsibility

Software engineers should not just be

concerned with technical considerations.

They have wider ethical, social and

professional responsibilities.

No clear rights and wrongs about many of

these issues.

(4)

Ethical Issues

9

Confidentiality

9

Competence

9

Intellectual property rights

9

Computer misuse

Software Engineering [IEEE90]

Software Engineering

is the systematic

approach to the development, operation, maintenance and retirement of software.

Software Engineering

means applications of a

systematic, disciplined, quantifiableapproach to development, operation, maintenance of software.

Notice

It implies a process since it points to different

phases

It stresses the need of a systematic and disciplined approach

It highlights the importance of quantification

Empirical studies and empirical methods are related to

the 3 mentioned aspects

Software Engineering [Boehm]

Software Engineering

is the application of

science and mathematics by which the capabilities of computer equipments are made useful to man via computer programs, procedures, and associated documentation.

(5)

Software Engineering

Deals with the economics of software

systems during the entire system life.

Provide methodologies for developing

software:

usable/useful to man in a repeatable way in an economic way

Cost Schedule and Quality

An engineering discipline is drive by

practical parameters:

9 cost

9 schedule 9 quality

They are conflicting requirements!

Cost

Is the cost of used resources: manpower,

hardware, software and support resources.

Manpower is predominant, software is still

labor intensive.

The cost is expressed in terms of person-month.

To obtain the project cost multiply the

number of person-month by the unit cost per person-month, this includes all the

overheads.

Schedule

Product time to market tends to be

reduced.

The cycle time from concept to delivery

should be small.

Often the window of opportunity is small

(e.g., financial applications).

New keywords:

Rapid Application

Development, COTS, Framework, …

(6)

Quality

Quality is not clearly understood, there

are three dimensions:

¾ product operation

¾ product transition

¾ product revision

Quality Factors

Pro_du ct t_ran siti_on Product operations Prod uct r evisi on Maintainability Flexibility Testability Portability Reusability Interoperability

Correctness Reliability Efficiency Integrity Usability

Product Operations

Correctness: to which extent the program

satisfies its specification.

Reliability: how well the software meets its

requirements.

Efficiency: response time, memory usage ... Usability: the effort to learn to operate with

the system

Integrity: ability to withstand attacks to its security

Product Revision

Maintainability: effort required to locate

and fix errors in an operating program.

Flexibility: effort required to modify an

operational program.

Testability: effort required to test, to

ensure that the system actually does

what it is supposed to do.

(7)

Product Transition

Portability: effort required to transfer

the software from one configuration to

other configurations.

Reusability: is the extent to which parts

of the software can be reused in other

related applications

Interoperability: effort required to

couple the system with other systems.

Quality Criteria

Among many indicators a de facto standard is

the reliability related measure of the number of defect per unit of size, i.e. 1000 LOC

¾ defect tracking is a key activity

¾ best software practice reduce to less than 1 defect per KLOC

Defect is a anything which is non compliant

with system requirements.

Consistency Problem

High quality, low cost in a short time

are the goals:

¾ How can we ensure a consistent

quality with a consistent productivity (i.e., cost and schedule)?

Engineering process model

Specification- set out the requirements and constraints on the system

Design- Produce a paper model of the system Manufacture- build the system

Test- check the system meets the required specifications

Install- deliver the system to the customer and ensure it is operational

(8)

The Software Engineering Approach

Develop methods and procedures for software development that can scale up for large system and that can be used to consistently produce high quality software at low cost and with a small cycle time.

Software Process Peculiarity

Normally, specifications are incomplete/anomalous

Very blurred distinction between specification, design and manufacture

No physical realization of the system for testing

Software does not wear out - maintenance does not mean component replacement

Process

A process is a particular methods of doing

Something generally involving a sequence of steps

Software process: the method of developing

software

Predictability

Predictability of a process determines

how accurately the outcome of

following a process in a project can be

predicted

before

the project is

completed:

cost and schedule estimate quality estimate

(9)

Predictability

Predictions are based on the past

history

Prediction are only probabilistic

Predictability is essential to ensure

consistency across many projects

Predictability is essential to ensure

repeatability

Statistical Control

A process is under statistical control if following the

same process produces similar results

Statistical control means that most projects will be

within a bound around the expected value

Projects Prope rty of i nte re st

.

_{. . . .}

.

_.

.

Software Process

A set of activities

A set of ordering constraints(among

activities)

activity are performed in accordance with ordering

constraints

the desired resultis obtained

low cost and high quality software

Software Process

Software Process Resources Product Idea Product

(10)

Process Key Properties

It must scale up (handle large software projects) It must produce good quality software

It must be cost effective It must deliver products on time It must be predictable

It must be repeatable

The Problem of Scale

Developing a very

large

system

requires very different set of methods

compared to developing a

small

system.

Methods for

small

systems generally

do not scale up

.

Counting people in a room or in a theater

or conducting a census

A Phased Approach

Separate developed product from development process.

Divide the entire process in a sequence of phases. Monitor each phase with objective methods:

¾ you cannot control what you cannot

measure

[Tom DeMarco]

Large Projects

Technology and methodology to develop the

system.

A formal approach to project management. A phased development process:

requirements analysis; software design; coding; testing;

(11)

High Level View

Inception

Elaboration

Transition Construction

The Problem of Scale

Formal

Informal

Informal Development methods Formal

Proj ect m anage m ent Small Project Large Project

Organizations and Processes

There are many non-software

engineeringprocesses running in an organization:

business processes training processes social processes

they influence software productionbut

do not concern software engineering

Development Process

Activities directly related to the software

production

requirement capture, design, coding testing

Components of the development process

for a particular phase are frequently called

methodologies

(12)

Software Process

The process that deals with the technical and management issues of software development is called software process There must be at least:

 development activities  project management activities Different people may perform different activities

Process Project Product

A

software process

specifies a method

of developing software

A

software project

is a development

project in which the software process is used

A

software product

is an outcome of a

software project obtained by applying a software process

Process Project Product - Again

A

software process

specifies an abstract

set of activities

A

software project

is the actual act of

executing the activities for some specific user need

A

software product

is any product

delivered during the software project

Process Project Product

Software Process

Project Project Project 1 k _n

(13)

Process Instantiation

Software process specifies a sequence of activity

at abstract level (not project specific)

A project implements, in a tailored fashion, the

“abstract software process”

The

project plan

is a detailed roadmap, for

the given project, that specifies: the specific activities to perform when perform the activities how perform the activities

Component Software Processes

We need to

develop

a software system

We need

manage

, to keep under

control the development process

We must

handle change requests

at

any arbitrary point in time

Beyond these activities (processes) there are other activities that are non-central: business processes, training processes, etc.

Component Software Processes

Process management process

Product engineering processes:

development process

project management process

software configuration (control) process

Process Management Process

A software process is a dynamic entity

The software process must adapt to new tools,

technologies

The software process must adapt to our increased

understanding about software development process management process aims to improve

software the software process i.e., produce better software at lower costs … HOW..?

(14)

Component Software Processes

Software Process Product Engineering Processes Process Management Process Development

Process ProjectManagement Process

Software Configuration Management Process

Effort Distribution

Requirements 10 % Design 20 % Coding 20 % Testing 50 %

Programmer Activities

Writing programs 13 % Reading programs and

manuals

16 % Job communication (e.g. meetings) 32 % Other (including parsonal) 39 %

Lesson Learnt

Coding covers only a fraction of

development costs

Development covers only a fraction of

entire life span cost

We must focus on maintenance and

testing to ensure cost effectiveness

develop for maintainability develop for testability

(15)

Defects

Defects are injected at

every stage

Defect prevention is a

key activity

Early defect removal is

mandatory to ensure cost effectiveness

Requirement analysys 20 %

Design 30 %

Coding 50 %

Defects Removal Costs

Requirements Design Code Development Test Acceptance Test Operation 2 5 10 50 100 1000

Defects Prevention

Prevent defect from being introduced Use the development process to learn (from

previous projects) so that methods of

performing activities, processes can effectively be improved

Quality Improvement Paradigm (QIP)

Software process operate in a closed-loop: the

process must learnt from past experiences: each project must feed information back to software

process for self-improvement

Improvement process

Assessment of the software process

Evaluation of a software process

improvement proposal

Software development/evolution is highly

human intensive it is very difficult to evaluate a change without human involvment

(16)

Empirical studies

Evaluate processes and human based

activities

Evaluate the use of software products

and tools

Experimentation provides a systematic,

quantifiable, controlled way of

evaluating human based activities

Research Methods [Basili]

The scientific method: observe the world,

build an observation based model

The engineering method: study the current

solutions, propose and evaluate changes

The empirical method: a model is proposed

and evaluated via case studies or experiments

The analytical method: a formal theory is

proposed and then compared with empirical observations

Empirical Study Cost

Different people are involved with different

activities/processes

Development, maintenance, evolution may be

performed in different environment companies by different people

We do not develop the same software … several

times …

Qualitative Research Paradigms

Qualitative studies: studying object in

their natural setting

We accept that there is a range of different

ways of interpretation

Aiming at discovering the causes noticed

by the subjects in the study

Subject is the person taking part in an

(17)

Quantitative Research Paradigms

Quantitative studies: quantifying a

relationship or compare two or more

groups

Identify cause effect relationship Setting up a formal experiment Case studies

Qualitative vs Quantitative

A quantitative study may be launched

to evaluate the reduction of defects

discovered in system testing due to the

adoption of a new testing tool suite

A qualitative study may attempt to

address the different source of

variations (e.g., unit testing, test

management,…)

Empirical Strategies

Setting up formal experiments

Studying real projects - also said

case studies

Performing surveys (e.g., is interviews)

Survey

Often an investigation performed in

retrospect – a tool or a technique has been in use for a while [Pfleeger]

Data are gathered via interviews

Interviews are done taking a representative

sampling of the population

The survey generalization limited to the

(18)

Survey Purposes

Descriptive:

to enable assertion about some population What the distribution is - We are not interested in

why the observed distribution exists

Explanatory

Making explanatory claim on the population - why

certain programmer prefer Java?

Explorative

A pre-study to ensure that important issues are

not foreseen

Case Study

Monitoring projects, activities or assignments.

Data is collected for a specific purpose

The level of control is lower in a case study than

in an experiment

In a case study the state variables only assume

one value which is governed by the actual project under study

Case Study Arrangements

Comparison against a company baseline

A sister project is chosen as baseline

If the method can be applied to individual

components, apply it at random to some components

Notice that the projects are not drawn at random from the population of all projects

Experiment

Experiment are carried out in a laboratory

environment

Subjects are assigned to different treatments

at random

Goal: manipulate one or more variables –

control all the other at fixed levels

The effect of the manipulation is measured

Quasi-experiment: we can not randomly

(19)

State Variable Example

Application domain: telecommunication,

database, operating systems

Programming language: C, Java, COBOL

Process: iterative, incremental, waterfall

Testing coverage criterion: statement,

functionality

Programmer experience: less that 5

years, 5 to 10 years …

Risk and Cost

Desktop survey: the change proposal is evaluated

off-line

There is no real change in the process People are not involved

Laboratory the change proposal is evaluated in a

laboratory setting (off line)

A limited part of the process is executed in a controlled

manner

Development projects: the change proposal is

evaluated in the real environment e.g., in a pilot project

Variable, Subject, Treatment

Dependent variables, or covariates, or response variables Independent variables, or variates, or factors this are manipulated Treatment: the particular level of a factor

Treatments are applied to a combination of objects and subjects Object: an artifact e.g., a design document

Subjects: the people that apply the treatment Test of trials: a combination of treatment, object, subject

Process Dependent variable Independent variables Fixed level

Experiment Principle [Trochim]

Theory

Observation Cause

Construct ConstructEffect

Treatment _Outcome Cause - effect Construct Treatment Outcome Construct

Independent Variable Dependent Variable Experiment goal

Experiment Operation

(20)

Experiment Process

Experiment Definition Experiment Planning Experiment Operation Analysis & Interpretation Presentation & Package Experiment Idea Conclusions

Analysis and Interpretation

Descriptive Statistics Data Set Reduction Hypothesis Testing Experimental Data Conclusions