Requirements Engineering

Requirements Engineering

requirements

a specification of the services a system should provide and the constraints on its operation

requirements engineering

process of finding out, analysing, documenting and checking requirements

user requirements 1

statements in natural language and diagrams

user requirements 2

what the system is expected to provide customers and the constraints under which it will operate

user requirements 3

written for customers

system requirements 1

structured document with details of what should be implemented

system requirements 2

can be part of contract between customer and developing organization

system requirements 3

functional and non-functional requirements, should be atomic and precise

functional requirements 1

what the system should or should not do

functional requirements 2

services the system should provide, how it should react to particular inputs and behave in particular situations

non functional requirements 1

specify or constrain characteristics of the system as a whole

non functional requirements examples

usability, performance, security

non functional requirements challenge 1

often proposed as general goals rather than measurable requirements

non functional requirements challenge 2

some requirements have no simple metrics

non functional requirements challenge 3

even if quantitative spec is possible, customers may not be able to relate their needs to them

non functional requirements challenge 4

cost of objectively verifying non functional requirements can be very high

speed metric

transactions/ second, response time to events

ease of use metric

training time, support features

reliability metric

mttf, availability, rocof

domain requirements 1

derived from system domain rather than user perspective

domain requirements 2

if domain requirements are not satisfied, system may be unusable

domain requirements challenge 1

understandability

domain requirements challenge 2

implicitness