System Modelling - L2

A requirement is (IEEE Std 610.12.-1990)

1. A condition or capability of a system needed by a user to solve a problem or achieve an objective;

2. A condition or capability that must be met or possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed document;

3. A documented representation of a condition or capability as in (1) or (2).

Requirements discovery identifies the scope and the major objectives of the

system.

> Requirements discovery is a finite phase in the development process.

Requirements gathering defines what is needed to reach those objectives.

> Requirement gathering is an ongoing activity throughout most of the

project.

Requirements fall into two broad categories

> Functional requirements: Functional requirements specify the behavior of the

system and the constraints on that behavior.

> Non-functional requirements: Non-functional requirements specify non-behavioral properties of the system and the constraints on those properties.

– Since both relate to the same system, they are interrelated and affect each other.

– The most top-level functional requirement expresses the mission of the system.

– Typically, a system provides a set of capabilities in order to accomplish the mission.

Usability

> Usability requirements specify how the behavior of the system must be

shaped in order to fit the users’ abilities and their work environment.

» Design of the user interface

Reliability

> Reliability requirements specify the dependability of the system both in time

and in the fulfillment of its functions.

Performance

> Performance requirements specify the response time and the input-output volume that that the system can handle within a particular timeframe

Maintainability

> Maintainability requirements specify the ability of the software to be modified and enhanced

Security

> Security requirements specify the right of access to the services of a system, the manner of access to those services, and the tracing of interactions with the system

- Interviews: focused or structured

- Questionnaires

- Workshops

- Field Trips and Observation

- Modeling

- Mock-Ups

- Interviewee profile

- Current environment

- General expectations

- constraints

- open-ended questions

- closed questions

- probes

- verification and recap