Categorias de requisitos

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System Requirements Fundamentals
Introduction Requirements Development Requirements Categories Writing Better Requirements

Requirements Fundamentals - Requirements Categories

(This work is based on material from many sources, including, Systems Engineering Course)

© André Mayoral, 2011 | helping systems happen... | all rights reserved

Importance of Requirement Types

Different types exist. Recognizing this fact implies:
    

Why different Types

Different fields of knowledge, Different analysis skills, Different spec techniques, Different solution techniques, Ability to change one thing without changing another

Requirements are responsible for most project failures*:

45% of failures due to requirements problems 2nd reason:11%
*Source: Standish Group,1996

All requirements problems are related to clarity of information

Ambiguity, transcriptions, different points-of-view

 

Making distinctions brings clarity Distinct requirement types brings clarity to specs

© André Mayoral, 2011 | helping systems happen... | all rights reserved

What is the categorization criteria?

Thiscategorization is based on the nature of the information, not in its origin. This helps each requirement to have only one place in a spec, thus avoiding:
  

Delays in searching for requirements Surprises: finding out that a requirement where it is not supposed to be Duplicity: having requirements in different places that:
  

Are the same, Have overlaps, Are conflicting!

© André Mayoral,2011 | helping systems happen... | all rights reserved

Types of Requirements
( (Organize your specification using one section for each requirement type)

Functional Performance States and modes Safety External Interface Environmental Resources Physical Verification Human Factors Reliability Maintainability Other Qualities Design

Description: requiredcharacteristics about...
What the item is to do How well a given function is to be performed Alternatives in behavior and their transitions How safely Cross-boundary items – inputs and outputs External environment conditions Which resources consumes/uses to do its job Physical properties – mass, dimensions, etc Required characteristics to enable verification How usable for humans How reliable Howmaintainable Other qualitative characteristics Directs the object’s design
Directs the design to allow economical production and consistent quality

© André Mayoral, 2011 | helping systems happen... | all rights reserved


© André Mayoral, 2011 | helping systems happen... | all rights reserved

Functional Requirements

Functional requirements state “what” the item is to “do”

Required Functions usually include:
   

Functional Requirement = a Required Function and its characteristics

normal operation functions, fault detection functions, fault recovery functions, and functions which deal with anomalous inputs change gear up (and it’s characteristics) keep cruise speed (and it’s characteristics) display instant fuel consumption

Function: Acharacteristic action to be performed by the item.

Functions usually can be viewed as transformations of some sort, from inputs into outputs.


A function may be performed in one or more mode

© André Mayoral, 2011 | helping systems happen... | all rights reserved

Performance Requirements
   

State “how well” a function is to be performed Relate onlyto functions Stated in quantitative terms Include:

Precision, response time, frequency, delays,...

 

Good practice: specify together with its related functional requirement Example:

“The landing gear shall retract in 10±1s”

© André Mayoral, 2011 | helping systems happen... | all rights reserved

Design Requirements

Define characteristics of the solution for the...
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