Chapter 4 terms

Closed interviews based on pre-determined list of questions Open interviews where various issues are explored with stakeholders.

Types of interview

are a kind of scenario that are included in the UML.

Use cases

These should provide detailed, specific information that is related to the application being developed; for example, hardware and database descriptions. Hardware requirements define the minimal and optimal configurations for the system. Database requirements define the logical organization of the data used by the system and the relationships between data.

Appendices

They should include descriptions of all facilities required.

Complete

There should be no conflicts or contradictions in the descriptions of the system facilities.

Consistent

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.

Design description languages

Constraints on the system from the domain of operation

Domain requirements

Training time Number of help frames

Ease of use

Be open-minded, avoid pre-conceived ideas about the requirements and are willing to listen to stakeholders. Prompt the interviewee to get discussions going using a springboard question, a requirements proposal, or by working together on a prototype system.

Effective interviewing

A social scientist spends a considerable time observing and analysing how people actually work.

Ethnography

Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc.

External requirements

Developed in a project studying the air traffic control process Combines ethnography with prototyping Prototype development results in unanswered questions which focus the ethnographic analysis.

Focused ethnography

Statements of services the system should provide, how the system should react to particular inputs and how the system should behave in particular situations.

Functional requirements

This should define the technical terms used in the document. You should not make assumptions about the experience or expertise of the reader.

Glossary

A general intention of the user such as ease of use.

Goal

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.

Graphical notations

Several indexes to the document may be included. As well as a normal alphabetic index, there may be an index of diagrams, an index of functions, and so on.

Index

This should describe the need for the system. It should briefly describe the system's functions and explain how it will work with other systems. It should also describe how the system fits into the overall business or strategic objectives of the organization commissioning the software.

Introduction

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. They cannot check that it represents what they want and are reluctant to accept it as a system contract

Mathematical specifications

The requirements are written using numbered sentences in natural language. Each sentence should express one requirement.

Natural language

Constraints on the services or functions offered by the system such as timing constraints, constraints on the development process, standards, etc.

Non-functional requirements

These define system properties and constraints e.g. reliability, response time and storage requirements. Constraints are I/O device capability, system representations, etc.

Non-functional requirements

Non-functional requirements may affect the overall architecture of a system rather than the individual components.

Non-functional requirements implementation

Requirements which are a consequence of organisational policies and procedures e.g. process standards used, implementation requirements, etc.

Organisational requirements

Percentage of target dependent statements Number of target systems

Portability

This should define the expected readership of the document and describe its version history, including a rationale for the creation of a new version and a summary of the changes made in each version.

Preface

Prioritising requirements and resolving requirements conflicts.

Prioritisation and negotiation

Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability, etc.

Product requirements

Mean time to failure Probability of unavailability Rate of failure occurrence Availability

Reliability

Groups related requirements and organises them into coherent clusters.

Requirements classification and organisation

Interacting with stakeholders to discover their requirements. Domain requirements are also discovered at this stage.

Requirements discovery

The process of gathering information about the required and existing systems and distilling the user and system requirements from this information.

Requirements discovery

Software engineers work with a range of system stakeholders to find out about the application domain, the services that the system should provide, the required system performance, hardware constraints, other systems, etc.

Requirements elicitation

Sometimes called requirements elicitation or requirements discovery. Involves technical staff working with customers to find out about the application domain, the services that the system should provide and the system's operational constraints. May involve end-users, managers, engineers involved in maintenance, domain experts, trade unions, etc. These are called stakeholders.

Requirements elicitation and analysis

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

Requirements engineering

Problems arise when functional requirements are not precisely stated.

Requirements imprecision

the process of managing changing requirements during the requirements engineering process and system development.

Requirements management

Requirements are documented and input into the next round of the spiral.

Requirements specification

The process of writing donw the user and system requirements in a requirements document.

Requirements specification

Concerned with demonstrating that the requirements define the system that the customer really wants.

Requirements validation

Verifiability comprehensibility traceability adaptability

Review checks

Time to restart after failure Percentage of events causing failure Probability of data corruption on failure

Robustness

Requirements that are derived from the way that people actually work rather than the way I which process definitions suggest that they ought to work.

Scope of ethnography

Mbytes Number of ROM chips

Size

Processed transactions/second User/event response time Screen refresh time

Speed

Requirements discovery, Requirements classification and organization, Requirements prioritization and negotiation, Requirements specification.

Stages of requirements elicitation

End users System managers System owners External stakeholders

Stakeholder types

The requirements are written in natural language on a standard form or template. Each field provides information about an aspect of the requirement.

Structured natural language

An approach to writing requirements where the freedom of the requirements writer is limited and requirements are written in a standard way.

Structured specifications

This chapter should present a high-level overview of the anticipated system architecture, showing the distribution of functions across system modules. Architectural components that are reused should be highlighted.

System architecture

This should describe the fundamental assumptions on which the system is based, and any anticipated changes due to hardware evolution, changing user needs, and so on. This section is useful for system designers as it may help them avoid design decisions that would constrain likely future changes to the system.

System evolution

This might include graphical system models showing the relationships between the system components and the system and its environment. Examples of possible models are object models, data-flow models, or semantic data models.

System models

A structured document setting out detailed descriptions of the system's functions, services and operational constraints. Defines what should be implemented so may be part of a contract between client and contractor.

System requirements

This should describe the functional and nonfunctional requirements in more detail. If necessary, further detail may also be added to the nonfunctional requirements. Interfaces to other systems may be defined.

System requirements specification

Any person or organization who is affected by the system in some way and so who has a legitimate interest

System stakeholders

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

Tabular specification

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. As far as possible, it should set of WHAT the system should do rather than HOW it should do it.

The software requirements document

are the descriptions of the system services and constraints that are generated during the requirements engineering process.

The system requirements

Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers.

User requirements

Here, you describe the services provided for the user. The nonfunctional system requirements should also be described in this section. This description may use natural language, diagrams, or other notations that are understandable to customers. Product and process standards that must be followed should be specified.

User requirements definition

A statement using some measure that can be objectively tested.

Verifiable non-functional requirement

It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification.

What is a requirement?