1

Introduction to Software Engineering

Preeti MishraCourse Instructor

Basics:Software & Software Engineering

What is Software?The product that software professionals build and then support over the long term.

Software encompasses:

(1) instructions (computer programs) that when executed provide desired features, function, and performance;

(2) data structures that enable the programs to adequately store and manipulate information and

(3) documentation that describes the operation and use of the programs.

Software products• Generic products

– Stand-alone systems that are marketed and sold to any customer who wishes to buy them.

– Examples – PC software such as editing, graphics programs, project management tools

• Customized products– Software that is commissioned by a

specific customer to meet their own needs.

– Examples – embedded control systems, air traffic control software, traffic monitoring systems.

Software Categories

• 1. System software: such as compilers, editors, file management utilities• 2. Application software: stand-alone programs for specific needs. • 3. Engineering/scientific software: Characterized by “number

crunching”algorithms. such as automotive stress analysis, molecular biology, orbital dynamics etc

• 4. Embedded software resides within a product or system. (key pad control of a microwave oven, digital function of dashboard display in a car)

• 5. Product-line software focus on a limited marketplace to address mass consumer market. (word processing, graphics, database management)

• 6. WebApps (Web applications) network centric software. As web 2.0 emerges, more sophisticated computing environments is supported integrated with remote database and business applications.

• 7. AI software uses non-numerical algorithm to solve complex problem. Robotics, expert system, pattern recognition game playing

Software—New Categories• Open world computing—pervasive, ubiquitous, distributed

computing due to wireless networking. How to allow mobile devices, personal computer, enterprise system to communicate across vast network.

• Netsourcing—the Web as a computing engine. How to architect simple and sophisticated applications to target end-users worldwide.

• Open source—”free” source code open to the computing community (a blessing, but also a potential curse!)

• Also … (see Chapter 31)– Data mining– Grid computing– Cognitive machines– Software for nanotechnologies

Why Software is Important?

• The economies of ALL developed nations are dependent on software.

• More and more systems are software controlled ( transportation, medical, telecommunications, military, industrial, entertainment,)

• Software engineering is concerned with theories, methods and tools for professional software development.

• Expenditure on software represents a

significant fraction of GNP in all developed countries.

Software costs

• Software costs often dominate computer system costs. The costs of software on a PC are often greater than the hardware cost.

• Software costs more to maintain than it does to develop. For systems with a long life, maintenance costs may be several times development costs.

• Software engineering is concerned with cost-effective software development.

Features of Software?• Its characteristics that make it different from

other things human being build.Features of such logical system: • Software is developed or engineered, it is not

manufactured in the classical sense which has quality problem.

• Software doesn't "wear out.” but it deteriorates (due to change). Hardware has bathtub curve of failure rate ( high failure rate in the beginning, then drop to steady state, then cumulative effects of dust, vibration, abuse occurs).

• Although the industry is moving toward component-based construction, most software continues to be custom-built.

• Modern reusable components encapsulate data and processing into software parts to be reused by different programs. E.g. graphical user interface, window, pull-down menus in library etc.

Wear vs. Deterioration

10

idealized curve

change

actual curve

Failurerate

Time

increased failurerate due to side effects

The IEEE definition:Software Engineering: (1) The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software; that is, the application of engineering to software. (2) The study of approaches as in (1).

The seminal definition:[Software engineering is] the establishment and use of sound engineering principles in order to obtain economically software that is reliable and works efficiently on real machines.

Software Engineering Definition

Importance of Software Engineering

• More and more, individuals and society rely on advanced software systems. We need to be able to produce reliable and trustworthy systems economically and quickly.

• It is usually cheaper, in the long run, to use software engineering methods and techniques for software systems rather than just write the programs as if it was a personal programming project. For most types of system, the majority of costs are the costs of changing the software after it has gone into use.

FAQ about software engineering

Question Answer

What is software? Computer programs, data structures and associated documentation. Software products may be developed for a particular customer or may be developed for a general market.

What are the attributes of good software? Good software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable.

What is software engineering? Software engineering is an engineering discipline that is concerned with all aspects of software production.

What is the difference between software engineering and computer science?

Computer science focuses on theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software.

What is the difference between software engineering and system engineering?

System engineering is concerned with all aspects of computer-based systems development including hardware, software and process engineering. Software engineering is part of this more general process.

Essential attributes of good software

Product characteristic Description

Maintainability • Software should be written in such a way so that it can evolve to meet the changing needs of customers.

• This is a critical attribute because software change is an inevitable requirement of a changing business environment.

Dependability and security • Software dependability includes a range of characteristics including • reliability, • security and • safety.

• Dependable software should not cause physical or economic damage in the event of system failure.

• Malicious users should not be able to access or damage the system.

Efficiency • Software should not make wasteful use of system resources such as memory and processor cycles.

• Efficiency therefore includes responsiveness, processing time, memory utilisation, etc.

Acceptability • Software must be acceptable to the type of users for which it is designed. • This means that it must be understandable, usable and compatible with other

systems that they use.

Questions!!

Software Process

A Layered Technology

a a ““qualityquality”” focus focus

process modelprocess model

methodsmethods

toolstools

Any engineering approach must rest on organizational commitment to quality which fosters a continuous process improvement culture.

Process Method Tools

Process, Methods, and Tools

• Process– Provides the glue that holds the layers together; enables

rational and timely development; provides a framework for effective delivery of technology; forms the basis for management; provides the context for technical methods, work products, milestones, quality measures, and change management

• Methods– Provide the technical "how to" for building software; rely on

a set of basic principles; encompass a broad array of tasks; include modeling activities

• Tools– Provide automated or semi-automated support for the

process and methods (i.e., CASE tools)

Process??

• (Webster) A system of operations in producing something; a series of actions, changes, or functions that achieve an end or a result

• (IEEE) A sequence of steps performed for a given purpose

What is a Software Process?• (SEI) A set of activities, methods, practices, and

transformations that people use to develop and maintain software and the associated products (e.g., project plans, design documents, code, test cases, and user manuals)

• As an organization matures, the software process becomes better defined and more consistently implemented throughout the organization

• Software process maturity is the extent to which a specific process is explicitly defined, managed, measured, controlled, and effective

Five Activities of a Generic Process framework

• Communication: communicate with customer to understand objectives and gather requirements

• Planning: creates a “map” defines the work by describing the tasks, risks and resources, work products and work schedule.

• Modeling: Create a “sketch”, what it looks like architecturally, how the constituent parts fit together and other characteristics.

• Construction: code generation and the testing. • Deployment: Delivered to the customer who evaluates the

products and provides feedback based on the evaluation.

• These five framework activities can be used to all software development regardless of the application domain, size of the project, complexity of the efforts etc, though the details will be different in each case.

• For many software projects, these framework activities are applied iteratively as a project progresses. Each iteration produces a software increment that provides a subset of overall software features and functionality.

Umbrella ActivitiesComplement the five process framework activities and help team manage

and control progress, quality, change, and risk.

1. Software project tracking and control: assess progress against the plan and take actions to maintain the schedule.

2. Risk management: assesses risks that may affect the outcome and quality.

3. Software quality assurance: defines and conduct activities to ensure quality.

4. Technical reviews: assesses work products to uncover and remove errors before going to the next activity.

5. Measurement: define and collects process, project, and product measures to ensure stakeholder’s needs are met.

6. Software configuration management: manage the effects of change throughout the software process.

7. Reusability management: defines criteria for work product reuse and establishes mechanism to achieve reusable components.

8. Work product preparation and production: create work products such as models, documents, logs, forms and lists.

The Essence of Practice• How does the practice of software engineering fit in the process

activities mentioned above? Namely, communication, planning, modeling, construction and deployment.

• George Polya outlines the essence of problem solving, suggests:

1. Understand the problem (communication and analysis).

2. Plan a solution (modeling and software design).

3. Carry out the plan (code generation).

4. Examine the result for accuracy (testing and quality assurance).

Understand the Problem

• Who has a stake in the solution to the problem? That is, who are the stakeholders?

• What are the unknowns? What data, functions, and features are required to properly solve the problem?

• Can the problem be compartmentalized? Is it possible to represent smaller problems that may be easier to understand?

• Can the problem be represented graphically? Can an analysis model be created?

Plan the Solution• Have you seen similar problems before? Are there

patterns that are recognizable in a potential solution? Is there existing software that implements the data, functions, and features that are required?

• Has a similar problem been solved? If so, are elements of the solution reusable?

• Can subproblems be defined? If so, are solutions readily apparent for the subproblems?

• Can you represent a solution in a manner that leads to effective implementation? Can a design model be created?

Carry Out the Plan

• Does the solutions conform to the plan? Is source code traceable to the design model?

• Is each component part of the solution provably correct? Has the design and code been reviewed, or better, have correctness proofs been applied to algorithm?

Examine the Result

• Is it possible to test each component part of the solution? Has a reasonable testing strategy been implemented?

• Does the solution produce results that conform to the data, functions, and features that are required? Has the software been validated against all stakeholder requirements?

Software Myths

Software Myths

Erroneous beliefs about software and the process that is used to build it.

•Affect managers, customers (and other non-technical stakeholders) and practitioners•Many people recognize the fallacy of the myths. Regrettably, habitual attitudes and methods •Poor management and technical practices, even when reality dictates a better approach.

Management Myths• We already have standards and procedures for

building software; isn’t that enough?– How widely used is it?– How relevant to the team?– How useful to the project?

• If we’re behind schedule, we’ll just add more programmers to catch up– “Adding people to a late project makes it later” [Brooks]– Ramp-up time– Interference

• If I outsource a project, I can just relax– Management issues are much more difficult, and if not

understood, will sink the project

Customer Myths• A general statement of work is sufficient to

kick off the project, and we can fill in the details later

• Requirements can change, and that’s OK because software is so flexible-Most software project failures can be traced to inadequacy of requirement specifications

Software Engineers’ Myths• Once the program is written, I’m done

– Between 60-80% of effort expended after delivery

• Until the program is written, quality is uncertain– Formal design reviews– Formal code reviews– Test-first approaches– Prototyping to verify design and structure– Prototyping to validate requirements

• The only deliverable is the program itself– Lots of documentation: installation guides, usage

guides, maintenance guides, API defintions and examples

Software Engineers’ Myths

• Documentation is Software-Engineering busy work– Focus is on quality, not quantity– Documentation can be hard for engineers to write,

just as C++ may be difficult for poets.

Legacy Software

What is Legacy System

• In computing, a legacy system is an old method, technology, computer system, or application program, "of, relating to, or being a previous or outdated computer system.“

• Often a pejorative term, referencing a system as "legacy" often implies that the system is out of date or in need of replacement.

Legacy Software - Characteristics• Support core business functions• Have longevity and business criticality• Exhibit poor quality

– Convoluted code, poor documentation, poor testing, poor change management

Why Organizations can have compelling reasons for keeping a legacy S/W

• The system works satisfactorily, and the owner sees no reason to change it.

• The costs of redesigning or replacing the system are prohibitive because it is large, monolithic, and/or complex.

• Retraining on a new system would be costly in lost time and money, compared to the anticipated appreciable benefits of replacing it

• The system requires near-constant availability, so it cannot be taken out of service, and the cost of designing a new system

• The user expects that the system can easily be replaced when this becomes necessary.

• Newer systems perform undesirable (especially for individual or non-institutional users)

Problems posed by legacy Software

• If legacy software runs on only antiquated hardware, the cost of maintaining the system may eventually outweigh the cost of replacing both the software and hardware unless

• These systems can be hard to maintain, improve, and expand because there is a general lack of understanding of the system; the staff who were experts on it have retired or forgotten what they knew about it, and staff who entered the field after it became "legacy" never learned about it in the first place. This can be worsened by lack or loss of documentation.

• Legacy systems may have vulnerabilities in older operating systems or applications due to lack of security patches being available or applied.

• Integration with newer systems may also be difficult because new software may use completely different technologies.

Reasons for Evolving the Legacy Software

• (Adaptive) Must be adapted to meet the needs of new computing environments or more modern systems, databases, or networks

• (Perfective) Must be enhanced to implement new business requirements

• (Corrective) Must be changed because of errors found in the specification, design, or implementation

(Note: These are also the three major reasons for any software maintenance)

End of Unit 1: Importance of Software Engineering

FAQ on Unit 1Type Examples

What/Define Software, Software Engineering, legacy Software, software process…..

list Software Myths, legacy s/w characteristics, generic process framework activities, umbrella activities…

Reason/ Why Use Software Engg, use process framework, use of legacy s/w, each s/w myth…

And in the similar way you can think of differences, advantages, limitations, examples ….. On these topics