REQUIREMENTS ENGINEERING

Question 1

What is requirements engineering

Answer 1

The process of establishing the services that the customer requires from a system and the constraints under which the system operates and is developed.

Question 2

What are requirements

Answer 2

 The requirements themselves are the descriptions of the system services and constraints that are generated during the requirements engineering process.
 It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification.

Question 3

What are the types of requirements?

Answer 3

 Functional requirements
 Non-functional requirements
 Domain requirements

Question 4

Describe functional requirements

Answer 4

 Describe functionality or system services the system should provide, how the system should react to particular inputs and how the system should behave in particular situations
 Depend on the type of software, expected users and the type of system where the software is used
 Functional user requirements may be high-level statements of what the system should do
 May state what the system should not do

Question 5

Give the examples of functional requirements eg for a Medical system

Answer 5

 A user shall be able to search the appointments lists for all clinics
 The system shall generate each day, for each clinic, a list of patients who are expected to attend appointments that day
 Each staff member using the system shall

Question 6

Describe the following concepts as relates to functional requirements: requirements imprecision, completeness and consistency

Answer 6

Imprecision-Ambiguous requirements may be interpreted in different ways by developers and users
 Consider the term ‘search’ in requirement 1
 User intention – search for a patient name across all
appointments in all clinics;
 Developer interpretation – search for a patient name in an individual clinic. User chooses clinic then search

Completeness
 They should include descriptions of all facilities required

Consistency
 There should be no conflicts or contradictions in the
descriptions of the system facilities
 In practice, it is impossible to produce a complete and
consistent requirements document

Question 7

Describe Non-Functional Requirements

Answer 7

 Constraints on the services or functions offered by the system such as timing constraints, constraints on the development process, standards, etc
 Often apply to the system as a whole rather than individual features or services
 These define system properties and constraints e.g. reliability, response time and storage requirements.
 Constraints are I/O device capability, system representations, etc.
 Process requirements may also be specified mandating a particular IDE, programming language or development method

Question 8

Describe and illustrate non-functional requirements classifications

Answer 8

 Product requirements
-Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability
 Organizational requirements
-Requirements which are a consequence of organizational policies and procedures e.g. process standards used, implementation requirements
 External requirements
-Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements

*See notes for the illustration

Question 9

Describe the implementation of non-functional requirements implementation

Answer 9

 Non-functional requirements may affect the overall
architecture of a system rather than the individual
components
 For example, to ensure that performance requirements are met, organize the system to minimize communications between components
 A single non-functional requirement, such as a security requirement, may generate a number of related functional requirements that define system services that are required
 It may also generate requirements that restrict existing requirements

Question 10

Give examples of non-functional requirements for example in a medical setting

Answer 10

Product requirement
The MoH-PMS shall be available to all clinics during normal working hours (Mon–Fri, 0830–17.30). Downtime within normal working hours shall not exceed five seconds in any one day.

Organizational requirement
Users of the MoH-PMS system shall authenticate themselves using their health authority identity card.

External requirement
The system shall implement patient privacy provisions as set out in the privacy act.

Question 11

Detail the metrics for specifying some non-functional requirements

Answer 11

1. Speed
   Processed transactions/second
   User/event response time
   Screen refresh time
2. Size
   Mbytes
   Number of ROM chips
   3.Ease of use
   Training time
   Number of help frames
   4.Reliability
   Mean time to failure
   Probability of unavailability
   Rate of failure occurrence
   Availability
   5.Robustness
   Time to restart after failure
   Percentage of events causing failure
   Probability of data corruption on failure
   6.Portability
   Percentage of target dependent statements
   Number of target systems

Question 12

Describe domain requirements

Answer 12

 The system’s operational domain imposes requirements on the system.
-For example, a train control system has to take into account the braking characteristics in different weather conditions
 Domain requirements may be new functional requirements, constraints on existing requirements or define specific computations

Question 13

What are some of the problems related to domain requirements

Answer 13

 Understandability
-Requirements are expressed in the language of the
application domain;
-This is often not understood by software engineers
developing the system

 Implicitness
 Domain specialists understand the area so well that they do not think of making the domain requirements explicit
9/12/2022 ICS 2201, Software Engineering 18

Question 14

What is the software requirements document

Answer 14

 This is the official statement of what is required of the
system developers.
 Should include both a definition of user requirements
and a specification of the system requirements. (User requirements have to be understandable by end-users and customers who do not have a technical background. System requirements may include more technical information.)
 It is NOT a design document. As far as possible, it should set of WHAT the system should do rather than HOW it should do it.

Question 15

How are requirements handled in agile methods

Answer 15

 Many agile methods argue that producing a requirements document is a waste of time as requirements change so quickly.
 The document is therefore always out of date.
 Methods such as XP use incremental requirements
engineering and express requirements as ‘user stories’
 The above is practical for business systems but problematic for systems that require a lot of pre-delivery analysis (e.g. critical systems) or systems developed by several teams

Question 16

Who are the users of the Requirements document?

Answer 16

System customers- To check if the requirements meet their needs and specify any changes
Managers- To plan the software development process
System Engineers- To understand what system is to be developed
System Test Engineers- To develop validation tests
System Maintenance engineers- to understand the system and the relationships between its parts

Question 17

What is a legal reason why Requirements specifications are needed?

Answer 17

 The requirements may be part of a contract for the system development
 It is therefore important that these are as complete as possible.
 They often form the basis for litigation when not accommodated!

Question 18

What are the different ways of writing a systems requirement specification

Answer 18

1.Natural language
2.Structured natural language
The requirements are written in natural language on a standard form or template. Each field provides information about an aspect of the requirement.
3.Design description languages
This approach uses a language like a programming language, but with more abstract features to specify the requirements by defining an operational model of
the system. This approach is now rarely used although it can be useful for interface specifications.
4.Graphical notations
Graphical models, supplemented by text annotations, are used to define the functional requirements for the system; UML use case and sequence diagrams are
commonly used.
5.Mathematical specifications
These notations are based on mathematical concepts such as finite-state machines or sets. Although these unambiguous specifications can reduce the ambiguity in a requirements document, most customers don’t understand a formal specification.

Question 19

What is the correlation between requirements and design

Answer 19

In principle, requirements should state what the
system should do and the design should describe how it does this.
 A system architecture may be designed to structure the requirements;
 The system may inter-operate with other systems that generate design requirements; Especially true when systems are ‘related’ or share same databases and files.
 The use of a specific architecture to satisfy non-functional requirements may be a domain requirement.
 The architecture may well be influenced by portability, scalability, maintainability, etc.
 This may be the consequence of a regulatory requirement

Question 20

Describe the natural language specification and its main advantage

Answer 20

The requirements are written using numbered sentences in natural language. Each sentence should express one requirement.
They are supplemented by diagrams
Used for writing requirements because it is expressive, intuitive and universal. This means that the requirements can be understood by users and customers.

Question 21

What are the problems involved with using natural language for requirements specification

Answer 21

 Lack of clarity
-Precision is difficult without making the document
difficult to read.
 Requirements confusion
-Functional and non-functional requirements tend to be
mixed-up.
 Requirements amalgamation
-Several different requirements may be expressed
together.

Question 22

Give an example of requirements for an insulin pump system specified in natural language

Answer 22

The system shall measure the blood sugar and deliver insulin, if required, every 10 minutes. (Changes in blood sugar are relatively slow so more frequent measurement is unnecessary; less frequent measurement could lead to unnecessarily high sugar levels.)

Question 23

Describe tabular specification

Answer 23

 Used to supplement natural language.
 Particularly useful when you have to define a number of possible alternative courses of action

Question 24

What are the stages of the requirements engineering process?

Answer 24

 Requirements elicitation;
 Requirements analysis;
 Requirements validation;
 Requirements management.