Non Functional Requirements-Software Requirement-Lecture Slides, Slides of Software Project Management

Download Non Functional Requirements-Software Requirement-Lecture Slides and more Slides Software Project Management in PDF only on Docsity!

Software Requirements

Lecture # 3

2

Kinds of Software Requirements• Functional requirements• Non-functional requirements• Domain requirements• Inverse requirements• Design and implementation constraints

4

NFRs as Goals

• Non-functional requirements are

sometimes written as general goals,which are difficult to verify

• They should be expressed

quantitatively using metrics (measures)that can be objectively tested

5

Example: Goal converted into an NFR

• Goal (unverifiable)
  • The system should be easy to use by

experienced controllers and should beorganized in such a way that user errors areminimized

• Non-functional requirement (verifiable)
  • Experienced controllers shall be able to use all

the system functions after a total of two hours’training. After this training, the averagenumber of errors made by experienced usersshall not exceed two per day

7

Metrics for NFRs - 1

Property

Measure

Speed

Processedtransactions/second

Response time

Screen refresh time

Requirements related to “Speed” can use differentmeasures to quantify the goal

8

Metrics for NFRs - 2

Property

Measure

Size

K bytes

Number of function points

Requirements related to “Size” can use different measuresto quantify the goal

10

Metrics for NFRs - 4

Property

Measure

Reliability

Mean time to failure

Probability ofunavailability

Rate of failure occurrence

Availability

Requirements related to “Reliability” can use differentmeasures to quantify the goal

11

Metrics for NFRs - 5

Property

Measure

Robustness

Time to restart after failure

Percentage of eventscausing failure

Probability of datacorruption on failure

Requirements related to “Robustness” can use differentmeasures to quantify the goal

13

Discussion on Metrics for NFRs

• With the help of these measures the NFRs

can be verified quantitatively

• It should also be noted that the cost of

quantitatively verifying each NFR may bevery high

14

Kinds of Software Requirements• Functional requirements• Non-functional requirements• Domain requirements• Inverse requirements• Design and implementation constraints

16

Domain Requirements - 1

• Requirements that come from the

application domain and reflectfundamental characteristics of thatapplication domain

• These can be both the functional or

non-functional requirements

17

Domain Requirements - 2

• These requirements, sometimes, are

not explicitly mentioned

• Domain experts find it difficult to

convey domain requirements

• Their absence can cause significant

dissatisfaction

19

Domain Requirements - 4

• Example:

In a commission-based salesbusinesses, there is no concept ofnegative commission. However, ifcare is not taken novice developers canbe lured into developing systems,which calculate negative commission

20

Domain Requirements - 5

• Banking domain has its own specific

constraints, for example, most banksdo not allow over-draw on mostaccounts, however, most banks allowsome accounts to be over-drawn