Requirements Engineering

Requirements Engineering

• Focus on customer needs, not on the solution or implementation
• Establishes the services that a customer requires from a system and the constraints under which it operates and is developed

Types of Requirements

• User Requirements:
  • Statements in natural language
  • Diagrams of the services the system provides
  • Operational constraints
  • Written for customers
• System Requirements:
  • A structured document
  • Detailed descriptions of the system’s functions, services, and operational constraints
  • Defines what should be implemented, may be part of a contract between client and contractor

System Stakeholders

• Any person or organization affected by the system in some way
• Stakeholder types:
  • End users
  • System managers
  • System owners
  • External stakeholders

Functional and Non-Functional Requirements

• Functional Requirements:
  • Describe functionality or system service
  • Written in natural language
  • Expand user requirements and are written as system requirements
  • Describe system functions, inputs, outputs, and exceptions in detail
• Non-Functional Requirements:
  • Constraints on the services or functions offered by the system
  • Timing constraints, development process, standards, etc.
  • Often apply to the system as a whole rather than individual features or services
  • May be more critical than functional requirements

Types of Non-Functional Requirements

• Product Requirements:
  • Specify or constrain the runtime behavior of the software
  • Specify that the delivered product must behave in a particular way (e.g., execution speed, reliability, security, and usability)
• Organizational Requirements:
  • Consequence of organizational policies and procedures
  • Define operational process requirements and development process requirements
• External Requirements:
  • Arise from factors external to the system and its development process
  • Examples: regulatory requirements, legislative requirements, ethical requirements

Requirements Engineering Processes

• Processes vary widely depending on the application domain, people involved, and organization
• Generic activities common to all processes:
  • Requirements elicitation
  • Requirements analysis
  • Requirements validation
  • Requirements management
• An iterative activity in which these processes are interleaved

Requirements Elicitation

• Understand the work that stakeholders do and how they might use a new system to support that work
• Activities:
  • Requirements discovery
  • Requirements classification and organization
  • Requirements negotiation
  • Requirements documentation