Lecture 12: Software Engineering

What You Will Learn Today

1. Describe the nature of computing and the software development process, including activities, models, roles and goals.
2. Describe recommended programming practices and factors relating to programmer productivity.
3. Design classes, relationships and object-oriented programs.

The Nature of Computing

• Is computing an art or craft? engineering? science?
• What is the difference between computer science and information technology?
• Do computer professionals
  • perform scientific experiments?
  • apply general principles?
  • follow professional standards?
• Programmers like to program but it's not the best solution for many problems.
  • It is your responsibility to focus on the needs of the customer, not on your own interests.
  • When all you have is a hammer, everything looks like a nail.

The Software Development Process

• The goal is to develop software products that are
  • correct, robust/reliable, fast/efficient, concise/lean/elegant, consistent, portable, easy to use; easy for other developers to read, reuse, extend, maintain
• The software development process directly influences the quality of the final product.
• The build-and-fix model: write program, modify program until ready to release
  • This method of developing software is common but is wasteful of time and resources and produces low quality software.
• A relatively small amount of development effort can save a lot of maintenance (fixing and improvement) effort.
  • An ounce of prevention is worth a pound of cure.
• The software development life cycle (SDLC) is often organized into activities.
• Software development activities include
  • project planning, analysis, requirements specification, design, implementation/coding, testing, debugging, installing, documenting
  • resource management, risk analysis, prototyping, simulations, models, benchmarks, validation and verification, training, supporting
• Software goes through several stages:
  • conception, development, release, use, testing, maintenance, retirement
• The waterfall model sees these activities as sequential or linear.
  • It should be used only for small, well-defined projects.
• The spiral model sees these activities as iterative.
  • Providing continuous feedback is necessary for larger projects.
• Roles involved in software development include
  • project managers, systems analysts, subject matter experts, programmers, technical writers, testers, end users

Development Process Goals

Develop an approach to software development that is:

• systematic, planned, methodical, consistent
• structured, organised, hierarchical
• logical, analytical, deductive, reasoned
• evaluative, diagnostic, problem-solving
• careful, precise, detail-oriented, accurate
• cooperative, communicative, team-oriented
• productive, minimalist, efficient, timely, cost-effective
• reflective, meta-cognitive, process-oriented

Recommended Programming Practices

• Realistic planning: Customers are to make business decisions, programmers are to make technical decisions. Update the plan when it conflicts with reality.
• Small releases: Release a useful system quickly, then release updates on a very short cycle.
• Metaphor: All programmers should have a simple shared story that explains the system under development.
• Simplicity: Design everything to be as simple as possible instead of preparing for future complexity.
• Testing: Both programmers and customers are to write test cases. The system is continuously tested.
• Refactoring: Programmers are to restructure the system continuously to improve the code and eliminate duplication.
• Pair programming: Put programmers together in pairs, and require each pair to write code on a single computer.
• Collective ownership: All programmers are to have permission to change all code as it becomes necessary.
• Continuous integration: Whenever a task is completed, build the entire system and test it.
• 40-hour week: Don't cover up unrealistic schedules with bursts of heroic effort.
• On-site customer: An actual customer of the system is to be accessible to team members at all times.
• Coding standards: Programmers are to follow standards that emphasize self-documenting code.

Source: Extreme Programming, Kent Beck, 1999, as listed in Horstmann p. 619

Programmer Productivity

• The best programmers in a team are commonly five to ten times as productive as the worst.
• Judgment, planning, knowledge, experience, and attention to detail make you a better programmer.
• Teamwork makes projects finish more slowly, but a team product is better than an individual product.

Prototyping

• A prototype is a relatively simple test program to explore the feasibility of a much larger program or project.
• A prototype is often used to test a user interface before implementing the processing parts.
• A prototype can help programmers and end users to uncover specification and design problems early.
• Prototypes are quickly and sloppily made, and usually thrown away after use.
• Resist the temptation of using prototypes as version 1 of the final product.

Steps for Designing Classes

1. Discover classes (concepts and their attributes)
2. Discover responsibilities of each class (methods)
3. Discover relationships between classes (any collaborative classes for each method)

• List these on index cards, one card per class, the class name on top, responsibilities on the left, relationships on the right.

Types of Relationships

• Unified Modeling Language (UML) is used to diagram relationships between classes.
• Draw a line between two related classes, with some way to indicate the type of relationship, e.g.:

Steps for Designing Object-Oriented Programs

• Gather requirements
• Design classes
• Use UML diagrams to show relationships
• Use Javadoc to document method behaviour and create a skeleton of the code
• Implement the code

To Do After Class

• Lab 10 and Project 2 are due Friday. Please complete all coursework by next Friday.
• The final examination is scheduled for December 17.
• Readings/References: Horstmann Ch. 16; Lewis & Loftus Ch. 10; Deitel & Deitel software engineering tips