WHO Dimension in System Design

Setting the Scene

• Requirements Engineering (RE) is concerned with understanding and defining a real-world problem, its context, and the desired machine's effect on the problem world.

The Problem World and the Machine Solution

• The problem world refers to the problematic part of the real world, consisting of human and physical components.
• The machine solution refers to the software and hardware to be developed and/or purchased to solve the problem.

The Problem World and the Machine Solution (continued)

• The world and the machine have their own phenomena, but share some others.
• RE is solely concerned with world phenomena, including shared ones.

System Versions

• There are two system versions: system-as-is (the current system) and system-to-be (the system as it should be when the machine operates).

RE: A Preliminary Definition

• RE is a coordinated set of activities for exploring, evaluating, documenting, consolidating, revising, and adapting the objectives, capabilities, qualities, constraints, and assumptions on a software-intensive system.

What Others Have Said

• Ross (1977) defined requirements definition as saying why a new system is needed, what system features will satisfy this context, and how the system is to be constructed.
• Zave (1997) defined RE as concerned with the real-world goals, functions, and constraints of software systems, and with their link to precise specifications of software behavior.

System Requirements vs. Software Requirements

• Software-to-be refers to the software to be developed, which is part of the machine and a component of the system-to-be.
• Environment refers to all other components of the system-to-be, including people, devices, and pre-existing software.

The WHY Dimension

• The WHY dimension involves identifying, analyzing, and refining the system-to-be's objectives to address the analyzed deficiencies of the system-as-is and in alignment with business objectives.

The WHAT Dimension

• The WHAT dimension involves identifying and defining the system-to-be's functional services to satisfy the identified objectives, according to quality constraints, and based on realistic assumptions about the environment.

The WHO Dimension

• The WHO dimension involves assigning responsibilities for the objectives, services, and constraints among system-to-be components, based on their capabilities and the system's objectives.

Setting the Scene (Summary)

• RE involves understanding the problem world and the machine solution, and scopes the WHY, WHAT, and WHO dimensions.
• RE involves descriptive and prescriptive statements, and categories of requirements, including functional and non-functional.
• The requirements lifecycle involves actors, processes, and products, and targets specific qualities and defects to avoid.

Identify responsibilities for objectives and services in a system among its components, considering their capabilities and system objectives. Examples include assigning tasks in an airport train control system.