Lecture 2: Software Process Models

Question 1

Building Vs. Growing

Answer 1

Building is when you plan everything before starting, but this does not always work well for software.

Growing software is better, because you start with a very simple system that runs, but with minimal functionality, and then continuously add on to that software and let it grow

Question 2

Steps of code and fix model

Answer 2

1. write some code
2. Fix them problems in the code.

Question 3

What are the drawbacks of code-and-fix model?

Answer 3

1. After fixes, code becomes poorly structured, which made fixing expensive
2. Even well designed software does not meet user’s need (you need a requirements phase)
3. Code was expensive to fix - poor prep for testing and modification

Question 4

What are the 5 phases of the waterfall process?

Answer 4

1. Requirements definition
2. system and software design
3. implementation and unit testing
4. integration and system testing
5. Operations and maintenance
   (These are all connected to each other)

Question 5

What is the original theory of the waterfall model?

Answer 5

One should move to the the next phase of development only when its preceding phase is completed and perfected

Question 6

What documents are generated from Waterfall process?

Answer 6

Each step will yield documents.
example: after finishing requirements analysis, a requirement document is generated, which is essential for later steps.

Question 7

What are common roles of Waterfall?

Answer 7

Analyst
Designer
Programmer
Tester
Trainer
Maintainer

Question 8

Why is cost-estimation tricky in Waterfall?

Answer 8

A problem is that we may not have enough information during the early phases to make accurate predictions about the effort needed, and hence the cost, of later phases.

Question 9

Why is waterfall a poor model?

Answer 9

The waterfall model is based on classical engineering practice: it is not clear that experience gained from construction of physical objects is going to work for software development
-the software development process is not well-understood;
scientific foundations are lacking;
software requirements change;
developers are HUMANS!

Driven by documents: Document reflects what reader wants to read rather than what is actually happening

Question 10

Pros and Cons of Waterfall process

Answer 10

Rigid and formal process, fits well for:
-Embedded systems
-Safety-critical systems

Activities are isolated:
-Late-changing requirements require a lot of rework!

Question 11

What’s the main medium of communication in waterfall model?

Answer 11

Verification
Documentation
Meetings
Feedback and Reviews

Question 12

Summarize prototype model

Answer 12

Design and build a prototype over and over until the customer approves the prototype and then the final design is done.

Question 13

Benefits of prototyping

Answer 13

Improved system usability.
A closer match to users’ real needs.
Improved design quality.
Improved maintainability.
Reduced development effort.

Question 14

Incremental development

Answer 14

Fancy name for “growing software.”

Question 15

Advantages of incremental development

Answer 15

There is a working system at all times;
clients can see the system and provide feedback
Progress is visible, rather than being buried in documents;
Some kinds of errors can be avoided.

Question 16

Errors and the moment they’re made

Answer 16

Errors made early in development tend to be more serious (more expensive to fix) than errors made later.

Question 17

The iterative process characteristic

Answer 17

Going small step by small step allows to uncover faulty assumptions early

Better at meeting customer’s needs: Some customers may not know what they actually want

Question 18

Characteristics of Incremental delivery

Answer 18

Rather than delivering the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality.

User requirements are prioritised and the highest priority requirements are included in early increments.

Question 19

What is incremental development and delivery?

Answer 19

Dev: Develop the system in increments and evaluate each increment before proceeding to the development of the next increment (before validating)
Increment: Deploy an increment for use by end-users (push to production)

Question 20

Advantages of incremental delivery

Answer 20

Customer value can be delivered with each increment so system functionality is available earlier.

Early increments act as a prototype to help elicit requirements for later increments.

Lower risk of overall project failure.

The highest priority system services tend to receive the most testing.

Question 21

Problems with Incremental delivery

Answer 21

Most systems require a set of basic facilities that are used by different parts of the system.
-As requirements are not defined in detail until an increment is to be implemented, it can be hard to identify common facilities that are needed by all increments.
The essence of iterative processes is that the specification is developed in conjunction with the software.
-However, this conflicts with the procurement model of many organizations, where the complete system specification is part of the system development contract.