XII. Non-Functional Requirements (or, Quality Factors)

Information Systems Analysis and Design

csc340

XII. Non-Functional Requirements (or, Quality Factors)

What are Non-Functional Reeqquuiirreemmeennttss ((NFRs)? Classification of NFRs Criteria and Factors

Portability, Reliability,, PPeerrffoorrmmaannccee Example NFR for an Automated Monneeyy MMaacchhiinnee

2003 John Mylopoulos

Non-Functional Requirements -- 1

Information Systems Analysis and Design

csc340

Non-Functional Requirements (NFRs)

Define global constraints on a software system, such as development costs, operational costs, performance, reliability, maintainability, portability, robustness etc.

Should not be confused with functional requirements, which impose requirements on the function of a system

Are generally stated informally, are often contradictory, difficult to enforce during development and to evaluate for the customer prior to delivery

How do we specify them?

2003 John Mylopoulos

Non-Functional Requirements -- 2

Page

Information Systems Analysis and Design

csc340

Types of NFRs

Interface requirements -- describe how the information system is to interface with its environment, users and other systems; include user interfaces and their qualities (e.g., "user-friendliness") Performance requirements -- describe performance constraints:

time/space bounds, such as workloads, response time, throughput and available storage space, e.g., "system must handle 1,000 transactions per second"); reliability involving the availability of components and integrity of information maintained and supplied to the system, e.g., "system must have less than 1hr downtime per three months" security, e.g., permissible information flows, who can do what; survivability, such as system will survive fire, natural catastrophes. Operating requirements -- include physical constraints (size, weight), personnel availability, skill level considerations, accessibility for maintenance, environmental conditions...

2003 John Mylopoulos

Non-Functional Requirements -- 3

Information Systems Analysis and Design

Types of NFRs

csc340

Lifecycle requirements -- can be classified under two subcategories:

Quality of the design, such as maintenability, enhanceability, portability; expected market or product lifespan,...(these don't affect initial system but may lead to increased maintenance costs or early obsolescence.)

Limits on development, other software lifecycle phases, such as development time limitations, resource availability, methodological standards etc.

Economic requirements -- immediate and/or long-term costs.

2003 John Mylopoulos

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Non-Functional Requirements -- 4

Information Systems Analysis and Design

csc340

(Different) Classification of NFRs

AAccqquuisisititioionnCCoonncceerrnn PPeerrfoforrmmaannccee

DDeessigignn AAddaappttaattioionn

UUsseer r CCoonncceerrnn RReessoouurrcceeuutitliilzizaatitoionn sseeccuurritiyty,,ccoonnfifdideennccee,,, ppeerrfoforrmmaanncceeuunnddeerrr aaddvveerrssitiyty,,eeaassee--ooff-f--uuussseee

CCoonnfoforrmmtotorereqqss??...... eeaassyytotorreeppaairir???......... vveerrifiifeieddppeerrfoforrmmaannccee??? EEaassyytotoeexxppaanndd?? .....u.uppggrraaddeefufunnccttitioioonnnooorrr ppeerrfoforrmmaannccee??? .....c.chhaannggee??.....i.ininntteteerrrffafaaccceee wwitihthaannooththeerrssyysstteteemmm??? .....p.poorrt?t?.....u.usseeiininnaaannnoootththheeerrr aapppplilcicaatitoionn??

QQuuaaliltityyFFaaccttoorrsss eefffifcicieiennccyy ininteteggrritiyty rerelilaiabbiliiltiyty ssuurvrvivivaabbiliiltiyty uussaabbiliiltiyty ccoorrrreecctntneessss mmaainintetennaabbiliiltiyty vveerirfiifaiabbiliiltiyty eexxppaannddaabbiliiltiyty flfelexxibibiliiltiyty ininteterrooppeerraabbiliiltiyty ppoorrtatabbiliiltiyty rereuussaabbiliiltiyty

2003 John Mylopoulos

Non-Functional Requirements -- 5

Information Systems Analysis and Design

csc340

Factors and Criteria

Factors are customer-related concerns, such as efficiency, integrity, reliability, correctness, survivability, usability,...

Criteria -- technical (development-oriented) concerns such as anomaly management, completeness, consistency, traceability, visibility,...

Each factor depends on a number of associated criteria, e.g., correctness depends on completeness, consistency, traceability,... verifiability depends on modularity, self-descriptiveness and simplicity

2003 John Mylopoulos

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Non-Functional Requirements -- 6

Information Systems Analysis and Design

csc340

(...A Year ago...) Canada - USA 5-2

2003 John Mylopoulos

Non-Functional Requirements -- 7

Information Systems Analysis and Design

Factors vs Criteria

csc340

factors -- customerrelated concerns criteria -- technical concerns

Reusability Portability Flexibility Verifiability Correctness Usability Survivability Reliability Integrity Efficiency

Factors

Criteria

Performance

Design Adaptation

Accuracy Performance

X

Anomaly Mngt

XX

Autonomy

X

Distributedness

X

Effectiveness storage X

Operability

X

System accessibility

X

Training

X

Completeness Design

X

Consistency

X

Traceability

X

Visibility

X

2003 John Mylopoulos

Non-Functional Requirements -- 8

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Information Systems Analysis and Design

Factors

csc340

Reusability Portability Flexibility Verifiability Correctness Usability Survivability Reliability Integrity Efficiency

Criteria

Performance

Applic. independAedanpcteation

Augmentability

Commonality

Doc. accessibility

Functional overlap

Functional scope

Generality

Independence

System clarity

System compatibility

Modularity

General

Self descriptiveness

Simplicity

X X

2003 John Mylopoulos

Design Adaptation

X

X

X XX

XX X

XXXX XXXX XX X

Non-Functional Requirements -- 9

Information Systems Analysis and Design

Quality Metrics

csc340

QQuuaaliltityy SSppeeeedd SSizizee EEaasseeooffUUssee RReelilaiabbiliiltityy RRoobbuussttnneessss PPoorrttaabbiliiltityy

MMeettrricic ttrraannssaaccttioionnss/s/seecc,,rreessppoonnsseettimimee ssccrreeeennrreeffrreesshhttimimee KKBByytteess nnuummbbeerrooffRRAAMMcchhipipss ttrraaininininggttimimee nnuummbbeerrooffhheelplpffrraammeess mmeeaann--ttimimee--ttoo--ffaailiulurree,,pprroobbaabbiliiltityyooffuunnaavvaailialabbiliiltityy rraatteeooffffaailiulurree,,aavvaailialabbiliiltityy ttimimeettoorreessttaarrttaafftteerrffaailiulurree ppeerrcceennttaaggeeooffeevveennttssccaauussininggffaailiulurree ppeerrcceennttaaggeeooffttaarrggeett--ddeeppeennddeennttssttaatteemmeennttss nnuummbbeerrooffttaarrggeettssyysstteemmss

2003 John Mylopoulos

Non-Functional Requirements -- 10

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