Requirement engineering

Description:

• The process of establishing the services that a customer requires from a system and the constraints under which it operates and is developed.
• The system requirements are the descriptions of the system services and constraints that are generated during the requirements engineering process.
• It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification.  
• This is inevitable as requirements may serve a dual function
  • May be the basis for a bid for a contract - therefore must be open to interpretation;
  • May be the basis for the contract itself - therefore must be defined in detail;

Types of requirements

• User vs system requirement
  • Business requirement
    • Key Performance Indicator
  • User requirements
    • Statements in natural language plus diagrams of the services the system provides and its operational constraints.
    • Written for customers.
  • System requirements
    • A structured document setting out detailed descriptions of the system’s functions, services and operational constraints.
    • Defines what should be implemented so may be part of a contract between client and contractor.
• Functional vs Non-functional requirement
• Domain requirement

Requirement engineering processes:

• 
• Requirement elicitation:
  • Sometimes called requirements elicitation or requirements discovery.
  • Involves technical staff working with customers to find out about the application domain, the services that the system should provide and the system’s operational constraints.
  • May involve end-users, managers, engineers involved in maintenance, domain experts, trade unions, etc. These are called stakeholders.
  • Software engineers work with a range of system stakeholders to find out about the application domain, the services that the system should provide, the required system performance, hardware constraints, other systems, etc.
  • Stages include:
    • Requirements discovery,
    • Requirements classification and organization,
    • Requirements prioritization and negotiation,
    • Requirements specification.

• Requirement specification:

• Requirement validation:

Requirement change: