XIV. Non-Functional Requirements

Information Systems Analysis and Design

csc340

XIV. Non-Functional Requirements

Classification of NFRs Criteria and Factors

Portability, Reliability, Performance Example NFR for an Automated Money Machine

2004 John Mylopoulos

Non-Functional Requirements -- 1

Information Systems Analysis and Design

csc340

Non-Functional Requirements -NFRs (also Software Qualities)

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 ccllaassssiiffyy tthheemm??

2004 John Mylopoulos

Non-Functional Requirements -- 2

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Information Systems Analysis and Design

csc340

Types of NFRs

Interface requirements -- how will the system interface with its environment, users and other systems; e.g., "user-friendliness". Performance requirements:

time/space bounds, such as workloads, response time, throughput and available storage space, e.g., "system must handle 1,000 transactions/sec"); reliability -- availability of components and integrity of data, e.g., "less than 1hr downtime/yr" security, permissible access to data and operations; survivability, such as system will survive fire, natural catastrophes. Operating requirements -- include physical constraints (size, weight), personnel availability, skill levels...

2004 John Mylopoulos

Non-Functional Requirements -- 3

Information Systems Analysis and Design

csc340

Types of NFRs (cont'd)

Lifecycle requirements -- can be classified under two sub-categories:

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 longterm costs.

2004 John Mylopoulos

Non-Functional Requirements -- 4

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Information Systems Analysis and Design

csc340

(Different) Classification of NFRs

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2004 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 associated criteria, e.g., Correctness depends on completeness, consistency, traceability,... Verifiability depends on modularity, self-description and simplicity

2004 John Mylopoulos

Non-Functional Requirements -- 6

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Information Systems Analysis and Design

csc340

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

2004 John Mylopoulos

Non-Functional Requirements -- 7

Information Systems Analysis and Design

Factors vs Criteria

csc340

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

factors -- customerrelated concerns criteria -- technical concerns

(Partial table)

2004 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

(Partial table)

2004 John Mylopoulos

Criteria

Performance

Design Adaptation

Applic. independAedanpcteation

Augmentability

Commonality

Doc. accessibility

Functional overlap

Functional scope

Generality

Independence

System clarity

System compatibility

Modularity

General

Self descriptiveness

Simplicity

X X

X

X

X XX

XX X

XXXX XXXX XX X

Non-Functional Requirements -- 9

Information Systems Analysis and Design

Quality Metrics

csc340

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2004 John Mylopoulos

Non-Functional Requirements -- 10

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