verhaert innovation day 2011 – joris vanderschrick (verhaert) - system requirements analysis

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INNOVATIONDAY 2011 Slide 1

System Requirements Analysis:The first step to value-based system development

Joris VanderschrickVerhaert - Embedded Systems [email protected]

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What is a system requirement?

1. A need: a process or improvement, thatstakeholders want to realize through a system.

2. A demand to a system: the behavior(= functionality) or quality (= performance) thata system must have to fulfil the need of the stakeholders.

Uit: Handboek Requirements

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The bridge function of requirements

Requirements

Stakeholders-) Business-) Customer-) Users…

Development Team

• Requirements: What the system must be able to do…

• Stakeholders: …to optimally be able to support us

• Development team: …and we have to implement them

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For who are requirements important?

Requirements

StakeholdersCustomer Service Provider

USERS DevelopmentTeam

Testers/Validation

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Users: The system must create Added Value

Utility

Desirability

Usability

Alowability

Feasibility

Add

ed V

alue

The ‘requirements’ must enable the developedsystem concept to create Added Value for the end-user

• What is the Added value of your product/system?

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What is the importance of requirements

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If you cannot manage to define the requirements at the start of a project, than itdoes not matter anymore how good you execute the following actions.

Importance of adequately defining the requirements

Phase Relative Correction costs

Requirements 1‐2

Technical Concept 5

Realisation 10

Unit Test 20

Acceptance Tst 50

Maintenance 50

Davis (1993)

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Conclusion: Leffingwell & Widrig (2003): Of the total budget for (software) development tasks, 25 to 40% will be spent on the correction of errors in the requirements.

Importance of ‘good’ requirements

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Criteria for well-defined requirements

Completeness:

Consistency:

No missing requirements: All the requirements, that the system must fulfil, must be defined

No conflicting requirements: Requirements can conflict when stakeholdershave different opinions about the specific demands for the systems

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Criteria for well-defined requirements

Unambiguity:

Validity:

• Only 1 interpretation possible of the requirements. • Not 100% possible Written in natural language

Requirements are only valid if they contribute to the added value for the stakeholders

“Around 45% of the developed functionality for a system is never used!”

“Don’t waste time with the overkill functionality.“

The Standish Group, 2003

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Requirements Analysis issues

The first step in the system engineering process: REQUIREMENTS ANALYSIS

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System Requirements Analysis

In the traditional waterfall model of system development, the first phase of requirements analysis is also the most important one.

Goal:

• Understanding the customer's business context and constraints• Functions the product must perform• The performance levels it must adhere to• The external systems it must be compatible with

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The System Engineering Process

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Origin Process Inputs

Analyze all aspects of the entire system life cycle including all equipments touch points with consumers, installers, service & maintenance staff

1. Customer Needs/Objectives/Demands

• Goals• Measures of Effectiveness• Environments• Constraints

2. Other:

• Technology Base• Output Requirements from Prior Development

Effort• Requirements Applied Through Specifications and Standards

Attract

Choose

UseSupport

Retain

Customer Needs ObjectivesDemands

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Key System Requirements

• Operational :

Where will the system be used?How long will the system be in use by the user?

• Environmental:

How are the various system components to be used? Utility!What environments will the system be expected to operate in an effective manner?

• Goal: How will the system accomplish its mission objective? Added Value!

• Performance:

What are the critical system parameters to accomplish the goal?How effective or efficient must the system be in performing its goal?

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Break-down requirements

• Items to be Developed: These are the primary requirements that will create the added value of the system. The biggest development efforts are initiated to fulfil these requirements.

• Specifications: Secundary development Items: These are the quantified requirements that do not need much development effort. They can immediately be fulfilled by existing components or sub-systems. Usually purchasing parts.

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Holistic approach

• Define the Functional & Performance requirements

• Define Design constraints• Define the Interface requirements

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Define functional and performance requirements

Functional requirements: What the system must do…Performance requirements: How well the system must perform…Break-down of the ITD

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Constraints & Interfaces

Define design constraints:

Limit Design flexibilityEnvironmental conditions & limitsStandards

Interface requirements:

Define the functional and physical interfaces to external or higher-level and interacting systems.

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FunctionalRequirements

Performance Requirements

CustomerRequirements

Security System for the Traffic Light Controller

FunctionalRequirements

Performance Requirements

CustomerRequirements

Interface System between traffic lights& Central for coördination

Traffic LightController IPC

Remote SecuritySystem

Central forcoordination

Interface Requirements

Interface Requirements

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Break-down requirements

Security System for the Traffic Controller (Traffic Lights)

Functional Requirements:

• Polling the Traffic Controller for Error• Analysis of the Error Messages• Routing the Error Messages to a Remote Central Security System

Performance Requirements:

• Polling speed (@1Hz)• Data transfer speed Error report available at remote system within 20 seconds• Redundant

Interface SystemFunctional Requirements:

• Receiving commands of the central system for the coordination of the Traffic Lights• Translating the specific command towards the protocol of the Traffic Controller

Performance Requirements:

• Reaction time between command & traffic lights change: <3 seconds

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Design constraints

• Easy serviceability & maintainability• Minor Assembly efforts• Re-use known company plaforms: Cirrus Logic ARM• Easy accessiblity• IP-67• No internal Airflow• System temperature up to 70°C.• Migration options for future communication upgrades• EN-50129 Safety related electronic systems for signaling

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Interface requirements

Routing the Error Messages to a Remote Central Security SystemReceiving commands of the central system for the coordination of the Traffic Lights

• Functional: IPC communication network to the Security & Interface system• Physical layer: Long-range wireless network or installed cable infrastructure

Polling the Traffic Controller for Error

• Functional: IPC communication network to the Traffic Controller• Physical layer: Short-range wireless network

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Functional Analysis & Allocation

• Clearly define the Global Framework and the different sub modules• Define successively lower-level functions• Allocate Performance and other limiting requirements • Defining/Refine functional architectures at ever-increasing levels of detail• Refine the Internal/External Functional Interfaces

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Functional Analysis Tool: FAST diagram

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Result: Functional Architecture

A Simple Rule:

Look to see if all the functions are verbs. If there is a function identified as a noun, then there is a problemwith the understanding of the functions.

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Refine Interface architecture

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Convert system architectures from Functional to Physical

Synthesis

• Physical decomposition defines the physical elements needed to execute the function.

• Define preferred physical solutions for the Primary and Secondary Development Items

• Define Internal and External Physical Interfaces

• Define Alternative System Concepts (Morphological map)

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Morphological mapAlternative Design ConceptsAlternative concepts can be defined via a Morphological map that provides a structure overview of the different Items to Be Developed (ITD’s) and the different options to develop them.

to a correct Risk Profile

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Example: Mobile Phone

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It is challenging to fix the concept, that will create the most Added Value in respect to a correct Risk profile. This is a very important task when defining the best System concept

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System Analysis and Verification

• Diverge: create a spectrum of requirements, sub-modules, functions, solutions,…Avoid fixation to 1 or 2 solutions Other options will become variations

• Verfication: Verify with the requirements, constraints, main goal, Added Value

• Converge: Trade-Off the different solutions and select

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System Specifications

• Add the Secundary Development Items• Clearly defined specifications and baselines• System Architecture• Concept Design• Decision Database

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verhaert innovation day 2011 – joris vanderschrick (verhaert) - system requirements analysis

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