Requirements

Requirements

Requirements Engineering

Elicitation

Analysis

Specification

Validation

User Stories

IEEE defines a requirement as:

A condition or capability needed by a user to solve a problem or achieve an objective

We would also describe requirements as:

• Agreement of work to be completed by all stakeholders
• Descriptions and constraints of a proposed system

Requirements

Functional requirements specify a specific capability/service that the system should provide. It's what the system does.

Non-functional requirements place a constraint on how the system can achieve that. Typically this is a performance characteristic.

Great reading on the topic

Functional v Non-Functional

For example:

Functional: The system must send a notification to all users whenever there is a new post, or someone comments on an existing post

Non-functional: The system must send emails no later than 30 minutes after from such an activity

Functional v Non-Functional

Requirements Engineering

We need a durable process to determine requirements

“The hardest single part of building a software system is deciding what to build. No part of the work so cripples the resulting systems if done wrong” (Brooks, 1987)

Requirements Engineering is:

• A set of activities focused on identifying the purpose and goal of a software system
• A negotiation process where stakeholders agree on what they want. Stakeholders include:
  • End user(s)
  • Client(s) (often businesses)
  • Design team(s)

Requirements Engineering

Requirements Engineering

RE | Step 1 | Elicitation

Questions and discovery

• Market Research
• Interviews with Stakeholders
• Focus groups
• Asking questions "What if? What is?"

RE | Step 2 | Analysis

Building the picture

• Identify dependencies, conflicts, risks
• Establish relative priorities
• Usually done through:
  • User stories (discussed today)
  • Use cases (discussed next week)

RE | Step 3 | Specification

Refining the picture

• Establishing the right sense of granularity
  • There is no perfect way to granulate
• Often the stage of breaking up into functional and non-functional
• E.G. Try and granulate "The system shall keep the door locked at all times, unless instructed otherwise by an authorised user.  When the lock is disarmed, a countdown shall be initiated at the end of which the lock shall be automatically armed (if still disarmed)"

RE | Step 4 | Validation

Going back to stakeholders and ensuring requirements are correct

Challenges during RE?

What are some challenges we may face while engaging in Requirements engineering?

• Requirements sometimes only understood after design/build has begun
• Clients/customers sometimes don't know what they want
• Clients/customers sometimes change their mind
• Developers might not understand the subject domain
• Limited access to stake holders
• Jumping into details or solutions too early (XY problem)

Let's step through an example