Software Engineering

Introduction

Why are you here?

• …alternatively, why do we think you need to be here?

• Why a course on software engineering?• How is real-world programming different than

what you have been doing so far?

Barry Boehm paper

• Read it before next class• Make sure you study it for the exams• Take notes!

What is SE?

• Software engineering (SE) is a profession “dedicated to designing, implementing, and modifying software so that it is of higher quality, more

affordable, maintainable, and

faster to build“

What’s wrong with the previous definition?

• A better definition: “SE is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software” – IEEE– Have you been doing this in your classes so far?

• Parnas (super famous CS guy) defined software engineering as the “multiperson construction of multiversion software”– Your projects so far were (probably) neither

multipurpose nor multiversion

Observations from/after Boehm

• Maintenance is expensive• Name three ways modern SW is different from

HW– Size, malleability, wear, novelty

• Fred Brooks– Accidental versus essential difficulties– No silver bullet; cannot be fixed by tools alone

Software project failure

• “Most” software projects fail• This failure is almost never due to developer

incompetence (alone)• If we are late, we can just add more people!• Who needs requirements; just start coding!• Requirements are malleable anyway!• And documentation just slows us down!• Besides, once we ship, we’re done!

No.

How can SE help?

• A set of tools and ideas that can increase the likelihood of success

So what are these tools/ideas?

• (things we will cover this semester)• A generic approach– Rigor and formality– Separation of concerns– Modularity– Abstraction– Anticipation of change– Generality– Incrementality

Leading to a Generic Framework• (things we will cover this semester)• Communication

– Heavy collaboration with the customer, other stakeholders and encompasses requirements gathering and related activities

• Planning– Establish a plan for the work. Technical task to be conducted, risks, needed

resources, work products to be created, and a schedule• Modeling

– Creation of models to allow the customer and the developer to better understand the requirements and design that will achieve those requirements

• Construction– Combines code generation and testing required to uncover errors in the code

• Deployment– The software (as a complete entity or partially complete increment) is

delivered to the customer who evaluates it and provides feedback.

And the framework is applied

• This is called the process model• The framework activities will always be

applied on every project ... BUT• The tasks (and degree of rigor) for each

activity will vary based on:– the type of project – characteristics of the project– common sense judgment; concurrence of the

project team

Example

• Which activities would you spend the most time on for– Space shuttle controller?– Web-based calendar?– Embedded controller in your refrigerator?– Daily fortune text messenger?

Framework Activities Communication Planning Modeling

Analysis of requirements Design

Construction Code generation Testing

Deployment

A basic model: Waterfall

• Benefit:– Easy to follow

• Limitation:– Often associated with project failure. Why might

that be?Communication

Planning

ModelingConstruction

Deployment analysis design code

test

project initiation requirement gathering estimating

scheduling tracking

delivery support feedback

Model types

• Prescriptive Models (like waterfall):– Want to limit and change– Provide repeatability/consistency– Coordinate teams

• Agile models– Respond to change– Working software rather than documentation– Individuals and interaction

• Which would you use for {a large team, a webapp, the space shuttle controller}?

Umbrella activities

• Software project management• Formal technical reviews• Software quality assurance• Software configuration management• Work product preparation and production• Reusability management• Measurement• Risk management