Reference: Sommerville, Software Engineering, 10 ed., Chapter 1

 

In theory, there is no difference between theory and practice. But, in practice, there is.

Software and software systems are everywhere. 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 tools for professional software development. Expenditure on software represents a significant fraction of GNP in all developed countries.

Applying software engineering principles helps address the two main factors of software failures:

Increasing demands

As new software engineering techniques help us to build larger, more complex systems, the demands change. Systems have to be built and delivered more quickly; larger, even more complex systems are required; systems have to have new capabilities that were previously thought to be impossible.

Low expectations

It is relatively easy to write computer programs without using software engineering methods and techniques. Computer programming is NOT software engineering.

What is software?

Computer programs 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 are the fundamental software engineering activities?

Software specification, software development, software validation and software evolution.

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.

What are the key challenges facing software engineering?

Coping with increasing diversity, demands for reduced delivery times and developing trustworthy software.

What are the costs of software engineering?

Roughly 60% of software costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs.

What are the best software engineering techniques and methods?

While all software projects have to be professionally managed and developed, different techniques are appropriate for different types of system. For example, games should always be developed using a series of prototypes whereas safety critical control systems require a complete and analyzable specification to be developed. You can't, therefore, say that one method is better than another.

What differences has the web made to software engineering?

The web has led to the availability of software services and the possibility of developing highly distributed service-based systems. Web-based systems development has led to important advances in programming languages and software reuse.

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.

Software engineering is an engineering discipline that is concerned with all aspects of software production from the early stages of system specification through to maintaining the system after it has gone into use. It is an engineering discipline because it uses appropriate theories and methods to solve problems bearing in mind organizational and financial constraints. Software engineering focuses on all aspects of software production and not just on the technical process of development; it includes project management and the development of tools, methods etc. to support software production.

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.

Any software process includes four types of activities:

• Software specification, where customers and engineers define the software that is to be produced and the constraints on its operation.
• Software development, where the software is designed and programmed.
• Software validation, where the software is checked to ensure that it is what the customer requires.
• Software evolution, where the software is modified to reflect changing customer and market requirements.

Heterogeneity

Increasingly, systems are required to operate as distributed systems across networks that include different types of computer and mobile devices.

Business and social change

Business and society are changing incredibly quickly as emerging economies develop and new technologies become available. They need to be able to change their existing software and to rapidly develop new software.

Security and trust

As software is intertwined with all aspects of our lives, it is essential that we can trust that software.

These software engineering fundamentals that apply to all types of software system:

Software process

Systems should be developed using a managed and understood development process. The organization developing the software should plan the development process and have clear ideas of what will be produced and when it will be completed. Of course, different processes are used for different types of software.

Focus on reliability

Dependability and performance are important for all types of systems. Software should behave as expected, without failures and should be available for use when it is required. It should be safe in its operation and, as far as possible, should be secure against external attack. The system should perform efficiently and should not waste resources.

Importance of requirements

Understanding and managing the software specification and requirements (what the software should do) are important. You have to know what different customers and users of the system expect from it and you have to manage their expectations so that a useful system can be delivered within budget and to schedule.

Leverage software reuse

You should make as effective use as possible of existing resources. This means that, where appropriate, you should reuse software that has already been developed rather than write new software.

Some issues of professional responsibility:

Confidentiality

You should normally respect the confidentiality of your employers or clients irrespective of whether or not a formal confidentiality agreement has been signed.

Competence

You should not misrepresent your level of competence. You should not knowingly accept work that is outside your competence.

Intellectual property rights

You should be aware of local laws governing the use of intellectual property such as patents and copyright. You should be careful to ensure that the intellectual property of employers and clients is protected.

Computer misuse

You should not use your technical skills to misuse other people's computers. Computer misuse ranges from relatively trivial (game playing on an employer's machine, say) to extremely serious (dissemination of viruses or other malware).

Software Engineering Code of Ethics and Professional Practice

Large Language Models (LLMs) like modern generative AI tools are rapidly becoming part of how software gets built and understood in practice. They do not replace the discipline of software engineering, but they are reshaping some activities within it-especially tasks involving natural language, pattern recognition, and synthesis.

At the most basic level, LLMs are prediction engines that generate text (including code and documentation) based on patterns learned from large corpora of human-produced data. They can:

• Generate or suggest code snippets given a problem description
• Summarize or explain requirements, design concepts, and sections of existing code
• Answer natural-language queries about a codebase or design problem

These uses touch on several traditional software engineering activities, such as specification, development, and validation.

However, many engineers do not fully trust LLM outputs and often still manually verify or discard generated code-because hallucinations, subtle bugs, and insecure patterns remain common.

In short: LLMs are tools that assist but are not substitutes for the engineering judgment, planning, and rigorous processes that define software engineering.

How LLMs change software engineering activities? Below are examples of how LLMs intersect with the core SE activities:

Specification (Understanding Needs)

LLMs can help translate vague requirements into clearer descriptions or highlight ambiguities in natural language. But they can also invent plausible-sounding requirements that don't reflect actual stakeholder needs-so human review is essential.

Development (Coding & Design)

LLMs may increase productivity when generating boilerplate code or handling unfamiliar languages. They often excel at filling in patterns (e.g., CRUD operations), but struggle with deep architectural reasoning and trade-off analysis-critical aspects of design.

Validation (Testing & Checking)

LLMs can suggest test cases or review code for obvious errors, but they are not reliable validators of correctness, performance, or security. AI-generated code frequently contains serious security flaws if deployed without careful checking.

Evolution (Maintenance & Change)

LLMs may assist in refactoring and documentation updates, but they don't have true understanding of long-term implications-only statistical associations. Interpretation and decision-making still lie with engineers.

Bottom line: LLMs can help with labor-intensive or language-oriented parts of software engineering work, but the core engineering judgment that determines what to build, why, and how well remains a human responsibility.

A simple guided example

Scenario:

You need to write a brief specification for a login feature.

Prompt to an LLM:

"Draft a specification for a secure user login feature that includes multi-factor authentication, error handling, and account lockout after failed attempts."

Typical Output (Excerpt):

"The system shall allow users to log in with username and password, and must support OTP via email or SMS as a second factor..."

Why this helps:

Quickly gives a draft structure. May remind you of elements you'd otherwise forget

Why this can mislead:

The model may assume OTP via SMS is secure (it isn't by modern standards). It may omit necessary details (rate limiting, encryption standards)

Discussion point:

What did the LLM get right, and where does it reflect weak or outdated engineering assumptions?

Key Takeaways

• LLMs can augment efficiency in software tasks involving language and pattern generation.
• They do not replace the core principles of software engineering such as requirement understanding, architectural reasoning, and dependability.
• Engineers must exercise judgment and verification, especially for security, correctness, and quality.