Systems Engineering Process Models

Chris Wallace

CPDA D6: Systems Engineering June 2005

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ISO 15288 processes

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5.4.2 Requirements Analysis Process

• Purpose– .. to transform the stakeholder, requirements-driven view of

desired system services into a technical view ..• Outcomes

– 1) the required characteristics, attributes, and functional and behavioural requirements for architectural design of a product solution are specified…

– 2-4• Activities

– 1. Define the functional boundary of the system in terms of acceptable organisational policies and procedures with respect to the Requirements Analysis process

– 2-8• < 2 pages in total

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ISO 15288 Example Lifecycle

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Alternative process models

• Contrasting process models – (links on web site)

– ISO 15288– The CADMIT process (MOD)– Boehm’s Spiral risk-driven model (Future

Combat systems)– Agile Modelling and XP (Object-oriented

Software)

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Spiral Model and Theory W• negotiation techniques are the most critical success factor in

improving the outcome of software projects. • The USC Center for Software Engineering has been developing a

negotiation-based approach to software system requirements engineering, architecture, development, and management.

• Components of the approach are:– Theory W, a management theory and approach, which says that making

winners of the system's key stakeholders is a necessary and sufficient condition for project success.

– The WinWin spiral model, which extends the spiral software development model by adding Theory W activities to the front of each cycle.

– WinWin, a groupware tool that makes it easier for distributed stakeholders to negotiate mutually satisfactory (win-win) system specifications.

• the WinWin spiral model is a good match for multimedia applications and is likely to be useful for other applications with similar characteristics--rapidly moving technology, many candidate approaches, little user or developer experience with similar systems, and the need for rapid completion.

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Some Basic Design ideas

• Christopher Alexander– Mathematician from Cambridge turned design theorist

then community architect and philosopher at Berkeley• Engineering approach to deducing a system architecture• Representation of design knowledge as Patterns• “every design problem begins with an effort to achieve fitness

between two entities: the form in question and its context. The form is the solution to the problem; the context defines the problem... The real object of discussion is not the form alone but the ensemble comprising the form and its context”

• “the form is a part of the world over which we have control, and which we decide to shape while leaving the rest of the world as it is. The context is that part of the world which puts demands on this form.. Fitness is the relation of mutual acceptability between these two..”

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Form / Context / Ensemble

Context (Alexander)

Form (Alexander)

Context System S1 (Martin)

Intervention SystemS2 (Martin)

Ensemble (Alexander)

Fitness (Alexander)System of Interest

(ISO 15288)

Real

Mental

Formal

3 Realms

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Context-R

Context-M

Context-F

Form-R

Form-M

Form-F

Real

Mental

Formal

Fitness-R

Fitness-F

Alexander’s model of design

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Classic staged process

• The core design task

• The basic staged model of development

• Validation and verification – the V Model

• Traceability

• Bridging the gap

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Fitness-F

Requirements

Constraints

Concept of Operations

Use cases and Scenarios

Domain Theories

Knowledge of materials processes mechanisms existing forms including COTS

Architecture

Models

Context-F

Goals

Form-F

Trade studies

Specifications

Design

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Context-R

Context-M

Context-F

Form-R

Form-M

Form-F

Real

Mental

Formal

Staged Development

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Context-R

Context-M

Context-F

Form-R

Form-M

Form-F

Real

Mental

FormalVerification

Validation

Validation and Verification

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Context-R

Context-M

Context-F

Form-R

Form-M

Form-F

Real

Mental

Formal

Traceability

Impact analysis Derivationanalysis

Choose Fx for Cy because

…

Design rationale

Coverage Analysis

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Context-R

Context-M

Stakeholder Requirements

Form-R

Form-M

Architectural Design

Real

Mental

FormalSystem

requirements

Intermediate Stages

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Concurrent models

• Concurrency arises from– Hierarchical decomposition– Product lifecycle– Multiple contexts and forms

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Hierarchy• Context / Form distinction is relative: Form at one level

becomes (part of) the Context for sub-forms

ISO 15288

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Form-M

Context-R

Context-M

Form-RReal

Mental

Formal

Form decomposition

P-R1 P-R2

P-F1 P-F2 P-F3

P-R3

P-M1 P-M2 P-M3

Context-F Form-F

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Context-RManufacture

Test

Repair

Multiple lifecycle contexts

Context-R

Context-R

Context-R

Context-R

Context-RDisposal

Use

Training

Form-R

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Multiple Contexts and Forms

• The context comprises multiple, nested interacting ‘systems’ arbitrarily bounded

• The form comprises not just system-of-interest but also support systems, training, documentation, servicing tools…

Context-Rc Form-RContext-RcContext-R

Context-R

Context-R

Context-R

Context-R

Form-R

Form-R

Form-R

Form-R

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Design for X 1

• Design for assembly• Design for disassembly• Design for ease of use• Design for EMC (ElectroMagnetic Compatibility)• Design for installation• Design for maintenance• Design for validation• Design for manufacture• Design for quality• Design for reliability• Design for reuse• Design for speed• Design for cost• Design for environment

1. www.betterproductdesign.net/guide/design4X.htm

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Complications

• Dynamics– The role of human cognition, social behaviour

and culture– Context is not fixed– Fitness is dynamic

• Form/Context separation is a myth

• Learning and feedback process models

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Context-M

Context-R

Context-M

Context-F

Form-R

Form-M

Form-F

Real

Mental

Formal

Human cognition in the system

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Context-R

Context-M

Context-F

Form-R

Form-M

Form-F

Real

Mental

Formal

Context is autonomous and dynamic

Context-F Form-FContext-F Form-F

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Context-R

Context-M

Context-F

Form-R

Form-M

Form-F

Real

Mental

Formal

Fitness is dynamic