AP-1Venkat SubramaniamVenkat Subramaniam

7. Requirements

AP-2Venkat SubramaniamVenkat Subramaniam

Requirements?• Describes what the system should do• Its services and constraints

• A high-level specification of what’s expected of the system

• It should not dictate how the system should be implemented, however

AP-3Venkat SubramaniamVenkat Subramaniam

Types of Specification• User requirements

• System requirements– Functional spec

• Design specification– Adds more details and constraints to system

requirements

AP-4Venkat SubramaniamVenkat Subramaniam

Who is it intended for?• User Requirements

– Managers, end users, developers, architects

• System requirements– End users, developers, architects

• Design Specification– Developers, architects

AP-5Venkat SubramaniamVenkat Subramaniam

Types of Requirements• Functional

– Behavior and interaction of the system– What it is supposed to do

• Non-functional– Constraints on the services– Performance, concurrency, standards, etc.

• Domain– Domain specific constraints– May be functional or non-functional

AP-6Venkat SubramaniamVenkat Subramaniam

Functional requirements• Specifies the interaction with the system

• Detailed list of what can be done using the application

• Users may not be very specific though expected to be precise

• Developers often misinterpret• Requirements often change or are

modified – leading to increased cost

AP-7Venkat SubramaniamVenkat Subramaniam

Non-functional Requirements• Stem from constraints, not from

specifications

• System related constraints– Reliability, speed, performance, concurrency,

storage requirements, interface restrictions,…

• Generally at the system specification level and are mostly critical – has wide effect on the system’s success

AP-8Venkat SubramaniamVenkat Subramaniam

Non-functional Requirements …• Some of these may not be related to

application, but related to process

• Requirements on how the system is developed, documented, progress is monitored, etc.– consider a application that requires FDA

approval!

AP-9Venkat SubramaniamVenkat Subramaniam

Type of non-functional reqs.• Product requirements

– Usability– Efficiency: Performance, space, Concurrency– Reliability– Portability

• Organizational requirements– Delivery, implementation, standards

• External requirements– Interoperability, ethical, legislative, privacy,

safety

AP-10Venkat SubramaniamVenkat Subramaniam

Risks from non-functional reqs• Some of these are hard to verify

• Need to test often to make sure system meets these

• Nice if quantitative metrics can be created to measure these