Software Engineering Lecture

Chapter 1 (MIdterms)

“easy” systems

one developer, one user, experimental use only

“hard” systems

multiple developers, multiple users, products

Over a stream

easy, one person job​

Over River Severn

The techniques do not scale

1. Over a stream

2. Over River Severn …

Analogy with bridge building

complexity

Software engineering is about managing this _______________

UNIX

contains 4 million lines of code​

Windows

2000 contains 108 lines of code​

Computer programs and associated documentation​

What is softwarre?

Software Products

may be developed for a particular customer or may be developed for a general market

1. Generic

2. Bespoke

Software Products may be?

Generic

developed to be sold to a range of different customers

Bespoke (Custom)

developed for a single customer according to their specification

Software Engineering

is an engineering discipline which is concerned with all aspects of software production​

- adopt a systematic and organised approach to their work ​

- use appropriate tools and techniques depending on ​

• the problem to be solved, ​

• the development constraints and ​

• the resources available​

Software Engineers should:

• theory​

• fundamentals

Computer Science is Concerned with?

Software Engineering is Concerned with?

• the practicalities of developing​

  • delivering useful software

Computer Science Theories

insuffficient to act BUT is a foundation for practical aspects of software engineering

system engineering

software engineering is part of?

• hardware, ​

• software and ​

• process engineering

System engineering is concerned with all aspects of computer-based system development including:

System engineers are involved in:

1. system specification, ​

2. architectural design, ​

3. integration

4. deployment​

software process

a set of activities whose goal is the development or evolution of software

1. Specification

2. Development

3. Validation

4. Evolution

Generic activities in all software process are:

Specification

what the system should and its development constraints

Development

production of the software system

Validation

checking of the software is what the customer wants

Evolution

changing the software in response to changing demands

software process model

a simplified representation of a software process, presented from a specific perspective

1. Workflow perspective

2. Data-flow perspective

3. Role/action perspective

Examples of process perspectives:

Workflow perspective

represents inputs, outputs and dependencies ​

Data-flow perspective

represents data transformation activities ​

Role/Action perspective

represents the roles/activities of the people involved in software process

1. Waterfall​

2. Evolutionary development​

3. Formal transformation​

4. Integration from reusable components​

Generic Process Models:

60 %

how much are development costs?

40%

how much for testing cost

customer software

the evolution cost often exceeds development costs

Costs

it varies depending on the type of system being developed and the requirement of system attributes such as performance and system reliability

Distribution of Costs

depends on the development model that is used

Computer-Aided Software Engineering

What is CASE?

Computer-Aided Software Engineering

Software systems which are intended to provide automated support for software process activities, such as requirements analysis, system modelling, debugging and testing ​

Upper-Case

Tools to support the early process activities of requirements and design

Lower-Case

tools to support later activities such as programming, debugging and testing

attributes of good software

The software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable​

1. Maintainability​

2. Dependability​

3. Efficiency​

4. Usability

What are the attributes of good software?​

Maintainability

software must evolve to meet changing needs

Dependability

Software must be trustworthy

Efficiency

Software should not make a wasteful use of system resources

Usability

Software must be usable by the users for which it was designed

1. Legacy Systems

2. Heterogeneity

3. Delivery

Software engineering in the 21st century faces three key challenges:​

Legacy Systems

Old, valuable systems must be maintained and updated

Heterogeneity

Systems are distributed and include of hardware and software

Delivery

There is increasing pressure for faster delivery of software