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This article considers the activities of the [[Systems Approach (glossary)]] related to the analysis and selection of a prefered solution from possible solution options in detail. Any of the activities described below may need to be considered [[concurrently (glossary)]] with other activities in the Systems Approach.  The final article in this knowledge area, [[Applying the Systems Approach]], considers the dynamic aspects of how these activities are used as part of the Systems Approach and how this relates in detail to elements of Systems Engineering.
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'''''Lead Author:''''' ''Rick Adcock'', '''''Contributing Authors:''''' ''Brian Wells, Scott Jackson, Janet Singer, Duane Hybertson''
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[[File:PPI.png|thumb|250px|right|<center>The "Systems Approach Applied to Engineered Systems" knowledge area is graciously sponsored by PPI.<center>]]
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This topic is part of the [[Systems Approach Applied to Engineered Systems]] knowledge area (KA).  It describes knowledge related to the analysis and selection of a preferred {{Term|Solution (glossary)|solution}} from the possible options, which may have been proposed by [[Synthesizing Possible Solutions]].  Selected solution options may form the starting point for [[Implementing and Proving a Solution]]. Any of the activities described below may also need to be considered {{Term|Concurrently (glossary)|concurrently}} with other activities in the {{Term|Systems Approach (glossary)|systems approach}} at a particular point in the life of a {{Term|System-of-Interest (glossary)|system-of-interest}} (SoI).  
  
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The activities described below should be considered in the {{Term|Context (glossary)|context}} of the [[Overview of the Systems Approach]] topic at the start of this KA.  The final topic in this KA, [[Applying the Systems Approach]], considers the dynamic aspects of how these activities are used as part of the systems approach and how this relates in detail to {{Term|Element (glossary)|elements}} of {{Term|Systems Engineering (glossary)|systems engineering}} (SE).
  
 
==System Analysis==
 
==System Analysis==
System Analysis is an activity within the Systems Approach to evaluate one or more system artefacts created during the Systems Approach activities:
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{{Term|System Analysis (glossary)|System analysis}} is an activity in the systems approach that evaluates one or more {{Term|System (glossary)|system}} artifacts created during the activities involved in [[Synthesizing Possible Solutions]], such as:
*to define Assessment Criteria based on the required properties and behavior of an identified problem or opportunity system situation;
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* Defining {{Term|Assessment Criterion (glossary)|assessment criteria}} based on the required properties and behavior of an identified {{Term|Problem (glossary)|problem}} or {{Term|Opportunity (glossary)|opportunity}} system situation.
*to assess the Properties and Behavior of each candidate solution in comparison to these criteria;
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* Accessing the properties and behavior of each candidate solution in comparison to the criteria.
*to compare the assessment of the candidate solutions and to identify if any of them could resolve the problem or exploit the opportunities, and if so to select which ones should be explored further.
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* Comparing the assessments of the candidate solutions and identification of any that could resolve the problem or exploit the opportunities, along with the selection of candidates that should be further explored.
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As discussed in [[Synthesizing Possible Solutions]] topic, the problem context for an {{Term|Engineered System (glossary)|engineered system}} will include a logical or ideal system solution description. It is assumed that the solution that “best” matches the ideal one will be the most acceptable solution to the {{Term|Stakeholder (glossary)|stakeholders}}. Note, as discussed below, the “best” solution should include an understanding of {{Term|Cost (glossary)|cost}} and {{Term|Risk (glossary)|risk}}, as well as {{Term|Effectiveness (glossary)|effectiveness}}. The problem context may include a {{Term|Soft System (glossary)|soft system}} {{Term|Concept (glossary)|conceptual}} {{Term|Model (glossary)|model}} describing the logical elements of a system to resolve the problem situation and how these are perceived by different stakeholders (Checkland 1999). This soft context view will provide additional criteria for the analysis {{Term|Process (glossary)|process}}, which may become the critical issue in selecting between two equally effective solution alternatives.  
  
As discussed in [[Synthesizing Possible Solutions]] the problem context for an [[Engineered System (glossary)]] will include a logical or ideal system solution description.  It is assumed that the solution which “best” matches the ideal will be the most acceptable to the stakeholders.  Note, as discussed below “best” should include an understanding of cost and risk as well as effectiveness.  The problem context may include a [[Soft System (glossary)]] Conceptual Model describing the logical elements of a system to resolve the problem situation and how these are perceived by different stakeholders (Checkland 1999).  This soft context view will provide additional criteria for the analysis process, which may become the critical issues in selecting between two equally effective solution alternatives.  
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Hence, analysis is often not a one-time process of solution selection; rather, it is used in combination with problem understanding and solution {{Term|Synthesis (glossary)|synthesis}} to progress towards a more complete understanding of problems and solutions over time (see [[Applying the Systems Approach]] topic for a more complete discussion of the dynamics of this aspect of the approach).
  
===Effectiveness Analysis===
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==Effectiveness Analysis==
Effectiveness studies use the problem or opportunity system as a starting point.  
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Effectiveness studies use the problem or opportunity system context as a starting point.  
  
The effectiveness of a synthesized system solution will included performance criteria associated with the system primary functions. These are derived from the systems purpose in enabling the realisation of stakeholder needs in one or more wider system contexts.   
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The effectiveness of a synthesized system solution will include performance criteria associated with both the system’s primary and enabling {{Term|Function (glossary)|functions}}. These are derived from the system’s {{Term|Purpose (glossary)|purpose}}, in order to enable the realization of stakeholder needs in one or more, wider system contexts.   
  
For a [[Product System (glossary)]] there are a set of generic non functional qualities which are associated with different types of solution pattern or technology, e.g. safety, security, reliability, maintainability, useability, etc.   These criteria are often explicitly stated as part of the domain knowledge of related technical disciplines of technology domains.
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For a {{Term|Product System (glossary)|product system}}, there are a set of generic non-functional qualities that are associated with different types of solution patterns or technology, e.g., {{Term|Safety (glossary)|safety}}, {{Term|Security (glossary)|security}}, {{Term|Reliability (glossary)|reliability}}, {{Term|Maintainability (glossary)|maintainability}}, usability, etc. These criteria are often explicitly stated as parts of the {{Term|Domain (glossary)|domain}} knowledge of related technical disciplines in technology domains.
  
For a [[Service System (glossary)]] or [[Enterprise System (glossary)]] the criteria will be more directly linked to the identified user need or enterprise goals. Typical qualities for such systems include agility, resilience, flexibility, upgradeability, etc.
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For a {{Term|Service System (glossary)|service system}} or {{Term|Enterprise System (glossary)|enterprise system}}, the criteria will be more directly linked to the identified {{Term|User (glossary)|user}} needs or {{Term|Enterprise (glossary)|enterprise}} goals. Typical qualities for such systems include agility, {{Term|Resilience (glossary)|resilience}}, {{Term|Flexibility (glossary)|flexibility}}, upgradeability, etc.
  
In addition to assessments of the absolute effectiveness of a given solution system we must also be able to combine effectiveness with limitations of the cost and timescales included in the problem context. In general, the role of System Analysis is to identify those proposed solutions which can provide some effectiveness within the cost and time allocated to any given iteration of the Systems Approach, see [[Applying the Systems Approach]] for details. If none of the solutions can deliver effectiveness that justifies the proposed investment then it is necessary to return to the original framing of the problem. If at least one solution is assessed as sufficiently effective then a choice between solutions can be proposed.
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In addition to assessments of the absolute effectiveness of a given solution system, {{Term|Systems Engineer (glossary)|systems engineers}} must also be able to combine effectiveness with the limitations of cost and timescales included in the problem context. In general, the role of system analysis is to identify the proposed solutions which can provide some effectiveness within the cost and time allocated to any given {{Term|Iteration (glossary)|iteration}} of the systems approach (see [[Applying the Systems Approach]] for details). If none of the solutions can deliver an effectiveness level that justifies the proposed investment, then it is necessary to return to the original framing of the problem. If at least one solution is assessed as sufficiently effective, then a choice between solutions can be proposed.
  
===Trade-off studies===
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==Trade-Off Studies==
In the context of the definition of a system, a trade-off study consists of comparing the characteristics of each candidate system element to determine the solution that best globally balances the assessment criteria. The various characteristics analyzed are gathered in cost analysis, technical risks analysis, and effectiveness analysis (NASA 2007). Each class of analysis is the subject of the following topics:
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In the context of the definition of a system, a trade-off study consists of comparing the characteristics of each candidate system element to those of each candidate system {{Term|Architecture (glossary)|architecture}} in order to determine the solution that globally balances the assessment criteria in the best way. The various characteristics analyzed are gathered in cost analysis, technical risks analysis, and effectiveness analysis (NASA 2007). To accomplish a trade off study, there are a variety of methods, often supported by tooling. Each class of analysis is the subject of the following topics:
#[[Assessment Criterion (glossary)|Assessment criteria]] are used to classify the various candidate solutions between themselves. They are absolute or relative. For example: maximum cost per unit produced is cc$, cost reduction shall be x%, effectiveness improvement is y%, and risk mitigation is z%.
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* Assessment criteria are used to classify the various candidate solutions. They are either absolute or relative. For example, the maximum cost per unit produced is c$, cost reduction shall be x%, effectiveness improvement is y%, and risk mitigation is z%.
#'''Boundaries''' identify and limit the characteristics or criteria to be taken into account in the analysis. For example: kind of costs to be taken into account, acceptable technical risks, and type and level of effectiveness.
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* '''{{Term|Boundary (glossary)|Boundaries}}''' identify and limit the characteristics or criteria to be taken into account at the time of analysis (e.g., the kind of costs to be taken into account, acceptable technical risks, and the type and level of effectiveness).
#'''Scales''' are used to quantify the characteristics, properties, and/or criteria and to make comparisons. Their definition requires knowing the highest and lowest limits as well as the type of evolution of the characteristic (linear, logarithmic, etc.).
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* '''Scales''' are used to quantify the characteristics, properties, and/or criteria and to make comparisons. Their definition requires knowledge of the highest and lowest limits, as well as the type of evolution of the characteristic (linear, logarithmic, etc.).
#An [[Assessment Score (glossary)|assessment score]] is assigned to a characteristic or criterion for each candidate solution. The goal of the trade-off study is to succeed in quantifying the three variables (and their decomposition in sub-variables) of cost, risk, and effectiveness for each candidate solution. This operation is generally complex and requires the use of models.
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* An {{Term|Assessment Score (glossary)|assessment score}} is assigned to a characteristic or criterion for each candidate solution. The goal of the trade-off study is to succeed in quantifying the three variables (and their decomposition in sub-variables) of cost, risk, and effectiveness for each candidate solution. This operation is generally complex and requires the use of models.
#The '''optimization''' of the characteristics or properties improves the scoring of interesting solutions.
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* The '''optimization''' of the characteristics or properties improves the scoring of interesting solutions.
  
A decision-making process is not an accurate science and trade-off studies have limits. The following concerns should be taken into account:
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A decision-making process is not an accurate science; ergo, trade-off studies have limits. The following concerns should be taken into account:
*Subjective criteria: for example, the component has to be beautiful. What is a beautiful component?
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*Subjective Criteria – personal bias of the analyst; for example, if the component has to be beautiful, what constitutes a “beautiful” component?
*Uncertain data: for example, inflation has to be taken into account to estimate the cost of maintenance during the complete life cycle. What will be inflation for the next five years?
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*Uncertain Data – for example, inflation has to be taken into account to estimate the cost of maintenance during the complete {{Term|Life Cycle (glossary)|life cycle}} of a system; how can a systems engineer predict the evolution of inflation over the next five years?
*Sensitivity analysis: a global assessment score associated to every candidate solution is not absolute; it is recommended to get a robust selection by performing sensitivity analysis that considers small variations of assessment criteria values (weights). The selection is robust if the variations do not change the order of scores.
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*Sensitivity Analysis – A global assessment score that is designated to every candidate solution is not absolute; thus, it is recommended that a robust selection is gathered by performing a sensitivity analysis that considers small variations of assessment criteria values (weights). The selection is robust if the variations do not change the order of scores.
  
 
A thorough trade-off study specifies the assumptions, variables, and confidence intervals of the results.
 
A thorough trade-off study specifies the assumptions, variables, and confidence intervals of the results.
  
== Systems Principles of System Analysis==
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==Systems Principles of System Analysis==
  
From the discussions above, the following general [[Principles (glossary)]] of Systems Analysis can be defined:
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From the discussions above, the following general {{Term|Principle (glossary)|principles}} of systems analysis can be defined:
  
#Systems Analysis is based on Assessment Criteria based upon a Problem or Opportunity System description.
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*Systems analysis is an iterative activity consisting of trade studies made between various solution options from the systems synthesis activity.
##These criteria will be based around an Ideal System description, which assumes a [[Hard System (glossary)]] problem context can be defined.
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*Systems analysis uses assessment criteria based upon a problem or opportunity system description.
##Criteria must consider required system behaviour and properties of the complete solution, in all possible wider system contexts and environments.
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** These criteria will be based around an ideal system description that assumes a {{Term|Hard System (glossary)|hard system}} problem context can be defined.
##These must consider non functional issues such as system safety, security, etc.
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** The criteria must consider required system behavior and properties of the complete solution in all of the possible wider system contexts and environments.
##This idea system description may be supported by [[Soft System (glossary)]] descriptions, from which additional “soft” criteria may be defined, e.g. a stakeholder preference for or against certain kinds of solution, relevant social, political or cultural conventions to be considered in the likely solution environment, etc.
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** Trade studies require equal consideration to the primary system and the enabling system working as a single system to address the user need. These studies need to consider system requirements for Key Performance Parameters (KPPs), systems safety, security, and affordability across the entire life cycle.
#The assessment criteria should include as a minimum the constraints on cost and time scales acceptable to stakeholders; but may also include preferences for or against certain kinds of solution, etc.
 
#Trade studies provide a mechanism for conducting Analysis of alternative solutions.
 
##A trade Study should consider a “System of Assessment Criteria”, with appropriate awareness of the limitations and dependencies between individual criteria.
 
##Trade studies need to deal with both objective and subjective criteria.  Care must be taken to assess the sensitivity of the overall assessment to particular criteria.
 
==Linkages to other topics==
 
  
[[Applying the Systems Approach]]
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** This ideal system description may be supported by {{Term|Soft System (glossary)|soft system}} descriptions from which additional “soft” criteria may be defined (e.g., a stakeholder preference for or against certain kinds of solutions and relevant social, political, or cultural conventions to be considered in the likely solution environment, etc.).
 +
* At a minimum, the assessment criteria should include the constraints on cost and time scales acceptable to stakeholders.
 +
* Trade studies provide a mechanism for conducting analysis of alternative solutions.
 +
** A trade study should consider a “system of assessment criteria,” designating special attention to the limitations and dependencies between individual criteria.
 +
** Trade studies need to deal with both objective and subjective criteria. Care must be taken to assess the sensitivity of the overall assessment to particular criteria.
  
 
==References==  
 
==References==  
  
 
===Works Cited===
 
===Works Cited===
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Checkland, P.B. 1999. ''Systems Thinking, Systems Practice''. Chichester, UK: John Wiley & Sons Ltd.
  
 
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NASA. 2007. ''Systems Engineering Handbook'', Revision 1. Washington, D.C., USA: National Aeronautics and Space Administration (NASA). NASA/SP-2007-6105.
  
 
===Primary References===
 
===Primary References===
  
ISO/IEC 2008. ''[[ISO/IEC/IEEE 15288|Systems and software engineering -- System life cycle processes]]''. Geneva,
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ISO/IEC/IEEE. 2015. ''[[ISO/IEC/IEEE 15288|Systems and Software Engineering -- System Life Cycle Processes]]''. Geneva, Switzerland: International Organisation for Standardisation/International Electrotechnical Commissions/Institute of Electrical and Electronics Engineer. [[ISO/IEC/IEEE 15288]]:2015.
Switzerland: International Organisation for Standardisation / International Electrotechnical Commissions. [[ISO/IEC/IEEE 15288]]:2008.
 
  
Jackson, S., D. Hitchins and H. Eisner. 2010. "[[What is the Systems Approach?]]" INCOSE ''Insight.'' 13(1) (April 2010): 41-43.
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Jackson, S., D. Hitchins and H. Eisner. 2010. "[[What is the Systems Approach?|What is the systems approach?]]" INCOSE ''Insight,'' vol. 13, no. 1, April, pp. 41-43.
  
 
===Additional References===
 
===Additional References===
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None.
  
 
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<center>[[Synthesizing Possible Solutions|<- Previous Article]] | [[Systems Approach|Parent Article]] | [[Implementing and Proving a Solution|Next Article ->]]</center>
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<center>'''SEBoK v. 2.10, released 06 May 2024'''</center>
  
 
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[[Category:Part 2]][[Category:Topic]]
 
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[[Category:Systems Approach]]
 

Latest revision as of 22:21, 2 May 2024


Lead Author: Rick Adcock, Contributing Authors: Brian Wells, Scott Jackson, Janet Singer, Duane Hybertson


The "Systems Approach Applied to Engineered Systems" knowledge area is graciously sponsored by PPI.

This topic is part of the Systems Approach Applied to Engineered Systems knowledge area (KA). It describes knowledge related to the analysis and selection of a preferred solutionsolution from the possible options, which may have been proposed by Synthesizing Possible Solutions. Selected solution options may form the starting point for Implementing and Proving a Solution. Any of the activities described below may also need to be considered concurrentlyconcurrently with other activities in the systems approachsystems approach at a particular point in the life of a system-of-interestsystem-of-interest (SoI).

The activities described below should be considered in the contextcontext of the Overview of the Systems Approach topic at the start of this KA. The final topic in this KA, Applying the Systems Approach, considers the dynamic aspects of how these activities are used as part of the systems approach and how this relates in detail to elementselements of systems engineeringsystems engineering (SE).

System Analysis

System analysisSystem analysis is an activity in the systems approach that evaluates one or more systemsystem artifacts created during the activities involved in Synthesizing Possible Solutions, such as:

  • Defining assessment criteriaassessment criteria based on the required properties and behavior of an identified problemproblem or opportunityopportunity system situation.
  • Accessing the properties and behavior of each candidate solution in comparison to the criteria.
  • Comparing the assessments of the candidate solutions and identification of any that could resolve the problem or exploit the opportunities, along with the selection of candidates that should be further explored.

As discussed in Synthesizing Possible Solutions topic, the problem context for an engineered systemengineered system will include a logical or ideal system solution description. It is assumed that the solution that “best” matches the ideal one will be the most acceptable solution to the stakeholdersstakeholders. Note, as discussed below, the “best” solution should include an understanding of costcost and riskrisk, as well as effectivenesseffectiveness. The problem context may include a soft systemsoft system conceptualconceptual modelmodel describing the logical elements of a system to resolve the problem situation and how these are perceived by different stakeholders (Checkland 1999). This soft context view will provide additional criteria for the analysis processprocess, which may become the critical issue in selecting between two equally effective solution alternatives.

Hence, analysis is often not a one-time process of solution selection; rather, it is used in combination with problem understanding and solution synthesissynthesis to progress towards a more complete understanding of problems and solutions over time (see Applying the Systems Approach topic for a more complete discussion of the dynamics of this aspect of the approach).

Effectiveness Analysis

Effectiveness studies use the problem or opportunity system context as a starting point.

The effectiveness of a synthesized system solution will include performance criteria associated with both the system’s primary and enabling functionsfunctions. These are derived from the system’s purposepurpose, in order to enable the realization of stakeholder needs in one or more, wider system contexts.

For a product systemproduct system, there are a set of generic non-functional qualities that are associated with different types of solution patterns or technology, e.g., safetysafety, securitysecurity, reliabilityreliability, maintainabilitymaintainability, usability, etc. These criteria are often explicitly stated as parts of the domaindomain knowledge of related technical disciplines in technology domains.

For a service systemservice system or enterprise systementerprise system, the criteria will be more directly linked to the identified useruser needs or enterpriseenterprise goals. Typical qualities for such systems include agility, resilienceresilience, flexibilityflexibility, upgradeability, etc.

In addition to assessments of the absolute effectiveness of a given solution system, systems engineerssystems engineers must also be able to combine effectiveness with the limitations of cost and timescales included in the problem context. In general, the role of system analysis is to identify the proposed solutions which can provide some effectiveness within the cost and time allocated to any given iterationiteration of the systems approach (see Applying the Systems Approach for details). If none of the solutions can deliver an effectiveness level that justifies the proposed investment, then it is necessary to return to the original framing of the problem. If at least one solution is assessed as sufficiently effective, then a choice between solutions can be proposed.

Trade-Off Studies

In the context of the definition of a system, a trade-off study consists of comparing the characteristics of each candidate system element to those of each candidate system architecturearchitecture in order to determine the solution that globally balances the assessment criteria in the best way. The various characteristics analyzed are gathered in cost analysis, technical risks analysis, and effectiveness analysis (NASA 2007). To accomplish a trade off study, there are a variety of methods, often supported by tooling. Each class of analysis is the subject of the following topics:

  • Assessment criteria are used to classify the various candidate solutions. They are either absolute or relative. For example, the maximum cost per unit produced is c$, cost reduction shall be x%, effectiveness improvement is y%, and risk mitigation is z%.
  • BoundariesBoundaries identify and limit the characteristics or criteria to be taken into account at the time of analysis (e.g., the kind of costs to be taken into account, acceptable technical risks, and the type and level of effectiveness).
  • Scales are used to quantify the characteristics, properties, and/or criteria and to make comparisons. Their definition requires knowledge of the highest and lowest limits, as well as the type of evolution of the characteristic (linear, logarithmic, etc.).
  • An assessment scoreassessment score is assigned to a characteristic or criterion for each candidate solution. The goal of the trade-off study is to succeed in quantifying the three variables (and their decomposition in sub-variables) of cost, risk, and effectiveness for each candidate solution. This operation is generally complex and requires the use of models.
  • The optimization of the characteristics or properties improves the scoring of interesting solutions.

A decision-making process is not an accurate science; ergo, trade-off studies have limits. The following concerns should be taken into account:

  • Subjective Criteria – personal bias of the analyst; for example, if the component has to be beautiful, what constitutes a “beautiful” component?
  • Uncertain Data – for example, inflation has to be taken into account to estimate the cost of maintenance during the complete life cyclelife cycle of a system; how can a systems engineer predict the evolution of inflation over the next five years?
  • Sensitivity Analysis – A global assessment score that is designated to every candidate solution is not absolute; thus, it is recommended that a robust selection is gathered by performing a sensitivity analysis that considers small variations of assessment criteria values (weights). The selection is robust if the variations do not change the order of scores.

A thorough trade-off study specifies the assumptions, variables, and confidence intervals of the results.

Systems Principles of System Analysis

From the discussions above, the following general principlesprinciples of systems analysis can be defined:

  • Systems analysis is an iterative activity consisting of trade studies made between various solution options from the systems synthesis activity.
  • Systems analysis uses assessment criteria based upon a problem or opportunity system description.
    • These criteria will be based around an ideal system description that assumes a hard systemhard system problem context can be defined.
    • The criteria must consider required system behavior and properties of the complete solution in all of the possible wider system contexts and environments.
    • Trade studies require equal consideration to the primary system and the enabling system working as a single system to address the user need. These studies need to consider system requirements for Key Performance Parameters (KPPs), systems safety, security, and affordability across the entire life cycle.
    • This ideal system description may be supported by soft systemsoft system descriptions from which additional “soft” criteria may be defined (e.g., a stakeholder preference for or against certain kinds of solutions and relevant social, political, or cultural conventions to be considered in the likely solution environment, etc.).
  • At a minimum, the assessment criteria should include the constraints on cost and time scales acceptable to stakeholders.
  • Trade studies provide a mechanism for conducting analysis of alternative solutions.
    • A trade study should consider a “system of assessment criteria,” designating special attention to the limitations and dependencies between individual criteria.
    • Trade studies need to deal with both objective and subjective criteria. Care must be taken to assess the sensitivity of the overall assessment to particular criteria.

References

Works Cited

Checkland, P.B. 1999. Systems Thinking, Systems Practice. Chichester, UK: John Wiley & Sons Ltd.

NASA. 2007. Systems Engineering Handbook, Revision 1. Washington, D.C., USA: National Aeronautics and Space Administration (NASA). NASA/SP-2007-6105.

Primary References

ISO/IEC/IEEE. 2015. Systems and Software Engineering -- System Life Cycle Processes. Geneva, Switzerland: International Organisation for Standardisation/International Electrotechnical Commissions/Institute of Electrical and Electronics Engineer. ISO/IEC/IEEE 15288:2015.

Jackson, S., D. Hitchins and H. Eisner. 2010. "What is the systems approach?" INCOSE Insight, vol. 13, no. 1, April, pp. 41-43.

Additional References

None.


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