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==Introduction==
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'''''Lead Author:''''' ''Rick Adcock'', '''''Contributing Authors:''''' ''Scott Jackson, Janet Singer, Duane Hybertson''
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This article forms part of the [[Systems Thinking]] knowledge area (KA). It describes {{Term|Systems Concept (glossary)|systems concepts}}, knowledge that can be used to understand {{Term|Problem (glossary)|problems}} and {{Term|Solution (glossary)|solutions}} to support [[Systems Thinking|systems thinking]].
  
In this Topic we have organized the key System Concepts around the 8 principles defined in the [[System Concepts]] Knowledge Area Introduction.  A number of key sources have been used.  
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The {{Term|Concept (glossary)|concepts}} below have been synthesized from a number of sources, which are themselves summaries of concepts from other authors. Ackoff (1971) proposed a system of system concepts as part of {{Term|General System Theory (glossary)|general system theory}} (GST); Skyttner (2001) describes the main GST concepts from a number of {{Term|Systems Science (glossary)|systems science}} authors; Flood and Carlson (1993) give a description of concepts as an overview of systems thinking; Hitchins (2007) relates the concepts to {{Term|Systems Engineering (glossary)|systems engineering}} practice; and Lawson (2010) describes a system of system concepts where systems are categorized according to fundamental concepts, types, topologies, focus, {{Term|Complexity (glossary)|complexity}}, and roles.  
  
Ackoff (Ackoff, 1971) proposes a '''System of System Concepts''' to bring together the wide variety of concepts which have been proposed.  Ackoff’s concepts are written from a systems research perspective and can be a little abstract and hard to relate to practice.  (Skyttner, 2001) describes the main GST concepts proposed by a number of authors; (Flood and Carlson, 1993) give a description of concepts as an overview of systems thinking; (Hitchins, 2007) relates the concepts to Systems Engineering Practice.
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==Wholeness and Interaction==
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A {{Term|System (glossary)|system}} is defined by a set of {{Term|Element (glossary)|elements}} which exhibit sufficient {{Term|Cohesion (glossary)|cohesion}}, or "togetherness," to form a bounded whole (Hitchins 2007; Boardman and Sauser 2008).
  
==Wholeness==
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According to Hitchins, interaction between elements is the "key" system concept (Hitchins 2009, 60). The focus on interactions and {{Term|Holism (glossary)|holism}} is a push-back against the perceived {{Term|Reductionism (glossary)|reductionist}} focus on parts and provides recognition that in {{Term|Complex (glossary)|complex}} systems, the interactions among parts is at least as important as the parts themselves.
The definition of [[System (glossary)]] includes the fundamental concepts of a set of '''Elements''' which exhibit sufficient '''Cohesion''' (Hitchins, 2007) or '''Togetherness''' (Boardman and Sauser 2008) to form a '''Bounded''' whole.
 
  
A system exists in an [[Environment (glossary)]] which contains related systems and conditions:
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An {{Term|Open System (glossary)|open system}} is defined by the interactions between {{Term|System Element (glossary)|system elements}} within a {{Term|System Boundary (glossary)|system boundary}} and by the interaction between system elements and other systems within an {{Term|Environment (glossary)|environment}} (see [[What is a System?]]). The remaining concepts below apply to open systems.
*[[Closed System (glossary)]], has no relationships with the environment.
 
*[[Open System (glossary)]], shares '''Inputs''' and '''Outputs''' with its environment across the boundary.
 
  
System elements may be conceptual organizations of ideals in symbolic form or real objects, e.g. people, data, physical artifacts, etc. 
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==Regularity==
*'''Abstract''' system all elements are conceptual. 
 
*'''Concrete''' system contains at least two elements which are objects. 
 
  
Unless other wise stated, the remaining concepts below apply to open, concrete systems.
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{{Term|Regularity (glossary)|Regularity}} is a uniformity or similarity that exists in multiple entities or at multiple times (Bertalanffy 1968).  Regularities make science possible and {{Term|Engineering (glossary)|engineering}} efficient and effective. Without regularities, we would be forced to consider every natural and artificial system problem and solution as unique. We would have no scientific laws, no categories or taxonomies, and each engineering effort would start from a clean slate.  
  
==Behavior==
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Similarities and differences exist in any set or population. Every system problem or solution can be regarded as unique, but no problem/solution is in fact entirely unique. The nomothetic approach assumes regularities among entities and investigates what the regularities are. The idiographic approach assumes each entity is unique and investigates the unique qualities of entities, (Bertalanffy 1975).
===State===
 
Any quality or property of a system element is called an '''Attribute'''.  [[State (glossary)]] is a set of system attributes at a given time. A '''System Event''' describes any change to attributes of a system (or environment) and hence its state:
 
*'''Static''', a single state exists with no events. 
 
*'''Dynamic''', multiple possible Stable states exist.  A stable state is one in which a system will remain until another event occurs.
 
*'''Homeostatic''', system is static but its elements are dynamic. The system maintains its state by internal adjustments.
 
  
State can be monitored using '''State Variables''' attributes which indicate system state.  The set of possible combinations of State over time is called '''State Space'''.  State is generally '''Continuous''', but can be modeled using a '''Finite State Model''' (or '''State Machine''')
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A very large amount of regularity exists in both natural systems and {{Term|Engineered System (glossary)|engineered systems}}. [[Patterns of Systems Thinking|Patterns of systems thinking]] capture and exploit that regularity.
* '''Deterministic''' systems has a one-to-one mapping of state variables to state space, allowing future states to be predicted from past states.
 
* '''Non-Deterministic''' systems have a many-to-many mapping of state variables; future state cannot be predicted. This may be due to random changes in state, or because its structure is sufficiently complex that while it is deterministic it may take up different states due to very small (below our ability to measure) differences it starting state. 
 
The later is one definition of a [[Chaos (glossary)|Chaotic (glossary)]] system, e.g. stock market or weather, are examples whose past states can be explained using deterministic reasoning, but whose future states cannot be predicted with any certainty.
 
  
===System Events===
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==State and Behavior==
(Ackoff, 1971) considers '''Change''' to be how a system is affected by events, and '''Behavior''' as the effect a system has upon its environment.
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Any quality or property of a {{Term|System Element (glossary)|system element}} is called an {{Term|Attribute (glossary)|attribute}}. The {{Term|State (glossary)|state}} of a system is a set of system attributes at a given time.  A '''system event''' describes any change to the{{Term|Environment (glossary)|environment}} of a system, and hence its state:
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*'''Static''' - A single state exists with no events. 
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*'''Dynamic''' - Multiple possible stable states exist. 
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*'''Homeostatic''' - System is static but its elements are dynamic.  The system maintains its state by internal adjustments.
  
Three kind of '''System Change''' are described: we '''React''' to a request by turning on a light, or we '''Respond''' to darkness by deciding to turn on the light or we '''Act''' to turn on the lights at a fixed time, randomly or with discernable reasoning.
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A stable state is one in which a system will remain until another event occurs.
  
System [[Behavior (glossary)]] is a change which leads to events in itself or other systemsThus, action, reaction or response may constitute behavior in some casesSystems have varying levels of behavior.
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State can be monitored using state variables, {{Term|Value (glossary)|values}} of attributes which indicate the system state.  The set of possible values of state variables over time is called the "'state space'"State variables are generally continuous but can be modeled using a finite state model (or "state machine").   
  
==Survival Behavior==
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Ackoff (1971) considers "change" to be how a system is affected by events, and system {{Term|Behavior (glossary)|behavior}} as the effect a system has upon its environment. A system can
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*'''react''' to a request by turning on a light,
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*'''respond''' to darkness by deciding to turn on the light, or
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*'''act''' to turn on the lights at a fixed time, randomly or with discernible reasoning.
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A stable system is one which has one or more stable states within an environment for a range of possible events:
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* '''Deterministic''' systems have a one-to-one mapping of state variables to state space, allowing future states to be predicted from past states.
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* '''Non-Deterministic''' systems have a many-to-many mapping of state variables; future states cannot be reliably predicted. 
  
All systems act to continue to exist, behaving to sustain themselves in one or more alternative viable states.  Many natural or social systems have this goal, either consciously or as a '''Self Organizing''', arising from the interaction between elements.
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The relationship between determinism and system complexity, including the idea of {{Term|Chaos (glossary)|chaotic}} systems, is further discussed in the [[Complexity]] article.
  
[[Entropy (glossary)]] is the tendency of systems to move towards disorder or disorganization.  In physics entropy is used to describe how “organized” heat energy is “lost” into the “random” background energy of the surrounding environment, e.g. 2nd law of Thermodynamics. 
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==Survival Behavior==
  
A similar effect can be seen in engineered systemsWhat happens to a building or garden, which is left unused for any time?  Entropy can be used as a metaphor for aging, skill fade, obsolescence, miss-use, boredom, etc.
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Systems often behave in a manner that allows them to sustain themselves in one or more alternative viable statesMany natural or social systems have this goal, either consciously or as a "self organizing" system, arising from the interaction between {{Term|Element (glossary)|elements}}.
  
'''Negentropy''' describes the forces working in a system to hold off entropy.  [[Homeostasis (glossary)]] is the biological equivalent of this, describing behavior which maintains a Steady State or Dynamic Equilibrium. Examples of this process in nature include human cells, which maintain the same function while replacing their physical content at regular intervals.
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{{Term|Entropy (glossary)|Entropy}} is the tendency of systems to move towards disorder or disorganization.  In physics, entropy is used to describe how organized heat energy is “lost” into the random background energy of the surrounding environment (the 2nd Law of Thermodynamics)A similar effect can be seen in {{Term|Engineered System (glossary)|engineered systems}}.  What happens to a building or garden left unused for any time? Entropy can be used as a metaphor for aging, skill fade, obsolescence, misuse, boredom, etc.
  
Again this can be used as a metaphor for the fight against entropy, e.g. training, discipline, maintenance, etc.
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"Negentropy" describes the forces working in a system to hold off entropy. {{Term|Homeostasis (glossary)|Homeostasis}} is the biological equivalent of this, describing behavior which maintains a "steady state" or "dynamic equilibrium."  Examples in nature include human cells, which maintain the same function while replacing their physical content at regular intervals.  Again, this can be used as a metaphor for the fight against entropy, e.g. training, discipline, maintenance, etc.
  
Hitchins (Hitchins, 2007), describes the relationship between the viability of a system and the number of connections between its elements. In cybernetics, [[Variety (glossary)|variety (glossary)]] is used to describe the number of different ways elements can be control, dependent on the different ways in which then can be combined.  Hitchins concept of Connected Variety states that stability of a system increases with its connectivity (both internally and with its environment).
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Hitchins (2007) describes the relationship between the viability of a system and the number of connections between its elements. Hitchins's concept of connected variety states that stability of a system increases with its connectivity (both internally and with its environment). (See {{Term|Variety (glossary)|variety}}.)
  
 
==Goal Seeking Behavior==
 
==Goal Seeking Behavior==
  
===Goals and Objectives===
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Some systems have reasons for existence beyond simple survival.  Goal seeking is one of the defining characteristics of {{Term|Engineered System (glossary)|engineered systems}}:
  
Some systems have other reasons for existence, beyond simple survival.
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*A '''goal''' is a specific outcome which a system can achieve in a specified time
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*An '''objective''' is a longer-term outcome which can be achieved through a series of goals.
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*An '''ideal''' is an objective which cannot be achieved with any certainty, but for which progress towards the objective has {{Term|Value (glossary)|value}}.  
  
*A '''Goal''' is a specific outcome which a system can achieve in a specified time
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Systems may be single-goal seeking (perform set tasks), multi-goal seeking (perform related tasks), or reflective (set goals to tackle objectives or ideas). There are two types of goal seeking systems:
*An '''Objective''' is a longer term outcome which can be achieved through a series of goals.
 
*An '''Ideal''' is an objective which cannot be achieved with any certainty, but for which progress towards the objective has value.
 
  
Systems may be single goal seeking (perform set tasks), multi-goal seeking (perform related tasks) or reflective (set goals to tackle objectives or ideas). We define two types of goal seeking system:
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*{{Term|Purposive (glossary)|Purposive}} systems have multiple goals with some shared outcome.  Such a system can be used to provide pre-determined outcomes within an agreed time period.  This system may have some freedom to choose how to achieve the goal.  If it has memory, it may develop {{Term|Process (glossary)|processes}} describing the behaviors needed for defined goals.  Most machines or {{Term|Software (glossary)|software}} systems are purposive.
  
*[[Purposive (glossary)]] systems have multiple goals, with some shared outcome.  Such a system can be asked/used to provide pre-determined outcomes, within an agreed time period.  Such a system may have some freedom to choose how to achieve the goal.  If it has memory it may develop Processes describing the behaviors needed for defined goals.  Most machines or software systems are purposive.
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*{{Term|Purposeful (glossary)|Purposeful}} systems are free to determine the goals needed to achieve an outcome.  Such a system can be tasked to pursue objectives or ideals over a longer time through a series of goals.  Humans and sufficiently complex machines are purposeful.
  
*[[Purposeful (glossary)]] systems are free to determine the goals needed to achieve an outcome.  Such a system can be tasked to pursue Objective or Ideals over a longer time through a series of goals.  Humans, and sufficiently complex machines, are purposeful.
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==Control Behavior==
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{{Term|Cybernetics (glossary)|Cybernetics}}, the science of {{Term|Control (glossary)|control}}, defines two basic control mechanisms:
  
===Function===
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*'''Negative feedback''', maintaining system state against set objectives or levels.
  
Ackoff defines [[Function (glossary)]] as outcomes which contribute to goals or objectives.  To have a function, a system must be able to provide the outcome in two or more different ways (this is called '''Equifinity''').  
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*'''Positive feedback''', forced growth or contraction to new levels.
  
This view of function and behavior is common in system scienceIn this paradigm all system elements have behavior of some kind, but to be capable of functioning in certain ways requires a certain richness of behaviors.
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One of the main concerns of cybernetics is the balance between stability and speed of response.  A {{Term|Black-Box System (glossary)|black-box system}} view looks at the whole system. Control can only be achieved by carefully balancing inputs with outputs, which reduces speed of responseA {{Term|White-Box System (glossary)|white-box system}} view considers the {{Term|System Element (glossary)|system elements}} and their relationships; control mechanisms can be embedded into this structure to provide more responsive control and associated risks to stability.  
  
In most hard systems approaches (Flood and Carson, 1993) a set of functions are described from the problem statement, and then associated with one or more alternative element structures.  This process may be repeated until system a [[Component (glossary)]] (implementable combinations of function and structure) have been defined (Martin, 1997).  Here '''Function''' is defined as a task or activity that must be performed to achieve a desired outcome; or as a '''Transformation''' of '''Inputs''' to '''Outputs'''This transformation may be:
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Another useful control concept is that of a "meta-system", which sits over the system and is responsible for controlling its functions, either as a black-box or white-box.  In this case, behavior arises from the combination of system and meta-system.   
  
*'''Synchronous''', a regular interaction with a closely related system.
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Control behavior is a trade between:
  
*'''Asynchronous''', an irregular response to a demand from another system, often triggering a set response.
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*'''Specialization''', the focus of system behavior to exploit particular features of its environment, and
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*{{Term|Flexibility (glossary)|Flexibility}}, the ability of a system to adapt quickly to environmental change.
  
The behavior of the resulting system is then assessedIn this case behavior is seen as an external property of the system as a whole, and often describe as analogous to human or organic behavior (Hitchins, 2009).
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While some system elements may be optimized for specialization, a temperature sensitive switch, flexibility, or an autonomous human controller, complex systems must strike a balance between the two for best resultsThis is an example of the concept of {{Term|Dualism (glossary)|dualism}}, discussed in more detail in [[Principles of Systems Thinking]].  
  
==Control==
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{{Term|Variety (glossary)|Variety}} describes the number of different ways elements can be controlled and is dependent on the different ways in which they can then be combined.  The Law of Requisite Variety states that a control system must have at least as much variety as the system it is controlling (Ashby 1956).
[[Cybernetics (glossary)]], the science of control, defines two basic control mechanisms:
 
  
*'''Negative feedback''', maintaining system state against set objectives or levels.
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==Function==
  
*'''Positive feedback''', forced growth or contraction to new levels.
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Ackoff defines {{Term|Function (glossary)|functions}} as outcomes which contribute to goals or objectives.  To have a function, a system must be able to provide the outcome in two or more different ways. (This is called '''equifinality'''.)
  
One of the main concerns of cybernetics is the balance between stability and speed of response.  Cybernetic considers systems in three ways.  A [[Black-Box System (glossary)]]  view looks at the whole system, control can only be achieved by carefully balancing inputs with outputs which reduces speed of responseA [[White-Box System (glossary)]] view considers the system elements and their relationships; here control mechanisms can be imbedded into this structure giving more responsive control and associated risks to stability. A Grey-Box view sits between these two, with control exerted at the major sub-system level. Another useful control concept is that of a Meta-System, which sits over the system and is responsible for controlling its functions, either as a black-box or white-box.  In this case behavior arises from the combination of system and meta-system.
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This view of function and {{Term|Behavior (glossary)|behavior}} is common in systems scienceIn this {{Term|Paradigm (glossary)|paradigm}}, all system elements have behavior of some kind; however, to be capable of functioning in certain ways requires a certain richness of behaviors.
  
Systems behavior is influenced by [[Variety (glossary)]], in particular in its control functions (Hitchins, 2009).  The law of requisite variety (Ashby, 1956) states that a control system must have at least as much variety as the system it is controlling. The effect of variety on system behavior can often be seen in the relationship between:
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In most {{Term|Hard System (glossary)|hard systems}} approaches, a set of functions are described from the problem statement and then associated with one or more alternative element {{Term|Structure (glossary)|structures}} (Flood and Carson 1993).  This process may be repeated until a system {{Term|Component (glossary)|component}} (implementable combination of function and structure) has been defined (Martin 1997).  Here, function is defined as either a task or activity that must be performed to achieve a desired outcome or as a transformation of inputs to outputs. This transformation may be:
  
*'''Specialization''', the focus of system behaviour to exploit particular features of its environment.
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*'''Synchronous''', a regular interaction with a closely related system, or
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*'''Asynchronous''', an irregular response to a demand from another system that often triggers a set response.
  
*'''Flexibility''', the ability of a system to adapt quickly to environmental change.
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The behavior of the resulting system is then assessed as a combination of function and {{Term|Effectiveness (glossary)|effectiveness}}.  In this case, behavior is seen as an external property of the system as a whole and is often described as analogous to human or organic behavior (Hitchins 2009).
  
==Effectiveness, Adaptation and Learning==
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==Hierarchy, Emergence and Complexity==
A systems [[Effectiveness (glossary)]] is a measure of its ability to perform the functions necessary to achieve goals or objectives.  (Ackoff, 1971) defines this as the product of the number of combinations of behavior to reach a function and the efficiency of each combination.
 
  
(Hitchins, 2007) describes effectiveness as a combination of '''performance''' (how well a function is done in ideal conditions), '''availability''' (how often the function is there when needed) and '''survivability''' (how likely is it that the system will be able to use the function fully).
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System behavior is related to combinations of element behaviors.  Most systems exhibit '''increasing variety'''; i.e., they have behavior resulting from the combination of element behaviors.  The term "synergy," or weak {{Term|Emergence (glossary)|emergence}}, is used to describe the idea that the whole is greater than the sum of the parts.  This is generally true; however, it is also possible to get '''reducing variety''', in which the whole function is less than the sum of the parts (Hitchins 2007).  
  
An [[Adaptability (glossary)|Adaptive (glossary)]] System is one that is able to change itself or its environment if its effectiveness is insufficient to achieve its current or future goals or objectivesAckoff defines four types of adaptation, changing the environment or the system, in response to internal or external factors.  
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Complexity frequently takes the form of {{Term|Hierarchy (glossary)|hierarchies}}. Hierarchic systems have some common properties independent of their specific content, and they will evolve far more quickly than non-hierarchic systems of comparable size (Simon 1996).  A natural system hierarchy is a consequence of wholeness, with strongly cohesive elements grouping together forming structures which reduce complexity and increase {{Term|Robustness (glossary)|robustness}} (Simon 1962).
  
A system may also '''Learn''', improving its effectiveness over time, without any change in state or goal.
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{{Term|Encapsulation (glossary)|Encapsulation}} is the enclosing of one thing within another. It may also be described as the degree to which it is enclosed. System encapsulation encloses system elements and their interactions from the external environment, and usually involves a system boundary that hides the internal from the external; for example, the internal organs of the human body can be optimized to work effectively within tightly defined conditions because they are protected from extremes of environmental change.
  
==Hierarchy, Emergence and Complexity==
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Socio-technical systems form what are known as control hierarchies, with systems at a higher level having some ownership of control over those at lower levels.  Hitchins (2009) describes how systems form "preferred patterns" which can be used to enhance the stability of interacting systems hierarchies. 
  
System behavior is related to the combinations of element behaviors.  Most systems exhibit '''increasing variety''', they have behavior resulting from the combination of element behavior.  The term '''Synergy''', or weak emergence, is used to describe the idea that “the whole being greater than the sum of the parts”.  While this is generally true, it is also possible to get '''reducing variety''' in which the whole function is less than the sum of the parts.  
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Looking across a hierarchy of systems generally reveals increasing complexity at the higher level, relating to both the structure of the system and how it is used.  The term {{Term|Emergence (glossary)|emergence}} describes behaviors emerging across a complex system hierarchy.
  
Open Systems tend to form [[Hierarchy (glossary)|Hierarchies (glossary)]] of coherent System Elements, or Sub-Systems.  In natural system hierarchy is a consequence of wholeness, with strongly cohesive elements grouping together, forming structures which reduce complexity and increase robustness (Simons, 1962).  Soci-technical systems form '''Control Hierarchies''', with systems at a higher level having some ownership of control over those at lower levels.  (Hitchins, 2009) describes how systems form '''Preferred Patterns''' which can be used to the enhanced stability of interacting systems hierarchies. 
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==Effectiveness, Adaptation and Learning==
  
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Systems {{Term|Effectiveness (glossary)|effectiveness}} is a measure of the system's ability to perform the functions necessary to achieve goals or objectives.  Ackoff (1971) defines this as the product of the number of combinations of behavior to reach a function and the efficiency of each combination.
  
We take advantage of this by viewing systems using '''Systemic Resolution'''.  A system is characterized by its behavior in a wider system or environment and considered in detail as a set of sub-system Structures and Functions.  This system description is focused at a particular level of resolution.  We can change this level of resolution by focusing upon the wider system, or upon one of the sub-systems.  While this allows us to focus on a given system-of-interest we must take care to continue to take a '''holistic''' view of the wider system and environment.
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Hitchins (2007) describes effectiveness as a combination of '''performance''' (how well a function is done in ideal conditions), '''availability''' (how often the function is there when needed), and '''survivability''' (how likely is it that the system will be able to use the function fully).
  
When we look across a hierarchy of system we generally see increasing [[Complexity (glossary)]] at the higher level, relating to both the structure of the system and how it is usedThe terms [[Emergence (glossary)]] and [[Emergent Property (glossary)|Emergent Properties (glossary)]] are generally used to describe behaviors emerging across a complex system hierarchyThese last two ideas are fundamental to Engineered System and the Systems Approach, and are discussed in more detail in the related topics.
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System elements and their environments change in a positive, neutral or negative way in individual situationsAn {{Term|Adaptability (glossary)|adaptive}} system is one that is able to change itself or its environment if its effectiveness is insufficient to achieve its current or future objectivesAckoff (1971) defines four types of adaptation, changing the environment or the system in response to internal or external factors.  
  
==Practical Consideration==
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A system may also '''learn''', improving its effectiveness over time without any change in state or goal.
  
How do we apply know how to apply system concepts to an Engineered System? 
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==References==
  
All Systems Engineering texts, for example (INCOSE 2011), describe processes and activities based upon the application of [[Systems Thinking (glossary)]] to an [[Engineered System (glossary)]] context.  Often the link between the Systems Engineering and the Systems Thinking has become embedded in the detail and is not clear to those applying the processes.  The [[Systems Approach (glossary)]] and its links to the rest of the SEBOK is intended to provide a guide to this linkage.
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===Works Cited===
  
(Hitchins, 2007) proposes a set of necessary and sufficient questions to help ensure all systemic issues have been considered when assessing an existing or proposed system description. These questions attempt to relate system concepts to high level concerns more relevant to Systems Engineers.  
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Ackoff, R.L. 1971. "Towards a system of systems concepts," ''Management Science,'' vol. 17, no. 11.  
  
Hitchins '''Generic Reference Model''' asks questions under six heading based on these concepts, related to its Function (what it does) and Form (what the system is). Each question expanded into a number of more details questions related to system concepts:
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Ackoff, R. 1979. "The future of operational research is past," ''Journal of the Operational Research Society'', vol. 30, no. 2, pp. 93–104, Pergamon Press.
  
#'''Function: Mission Management'''. How does the system deal with setting of objectives and plans; control and behavior; relationships with other systems?
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Ashby, W R. 1956. "Chapter 11," in ''Introduction to Cybernetics''. London, UK: Wiley.
#'''Function: Viability Management'''. How does the system deal with state, survival, maintenance and repair?
 
#'''Function: Resource Management'''. How does the system deal with enchange of information, energy, people, material, finance, ect. with its environment?
 
#'''Form: Structure'''. Do we understand system boundaries, sub elements, connections and relationships?
 
#'''Form: Influence'''.  Do we understand the systems wider relationships and influences with its environment?
 
#'''Form: Potential'''. Have we considered the structure to achieve all objective, how often and well they must be done, and how we deal with faults or failures?
 
  
==References==
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Bertalanffy, L. von. 1968. ''General System Theory: Foundations, Development, Applications,'' Revised ed. New York, NY, USA: Braziller. 
  
===Citations===
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Bertalanffy, L. von. 1975. ''Perspectives on General System Theory.'' E. Taschdjian, ed. New York, NY, USA: George Braziller.
  
von Bertalanffy, L. 1968. General system theory: Foundations, development, applications. Revised ed. New York, NY: Braziller.
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Boardman, J. and B. Sauser. 2008. ''Systems Thinking: Coping with 21st Century Problems.'' Boca Raton, FL, USA: Taylor & Francis.  
  
Ackoff, R.L. 1971. Towards a System of Systems Concepts, Management Science, Vol.17 No. 11, USA.
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Flood, R.L. and E.R. Carson. 1993. ''Dealing with Complexity: An Introduction to the Theory and Application of Systems Science''. New York, NY, USA: Plenum Press.
  
Flood, R.L. and Carson, E.R. (1993) Dealing With Complexity: An Introduction to the Theory and Application of Systems Science. New York: Plenum Press
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Hitchins, D. 2007. ''Systems Engineering: A 21st Century Systems Methodology''. Hoboken, NJ, USA: John Wiley and Sons.
  
Hitchins, D. (2007) Systems Engineering: A 21st Century Systems Methodology: Wiley
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Hitchins, D. 2009. "[[What are the General Principles Applicable to Systems?|What are the general principles applicable to systems?]]" INCOSE ''Insight,'' vol. 12, no. 4, pp. 59-63.
  
Hitchins, Derek. 2009. What are the General Principles Applicable to Systems? Insight, 59-63.
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Lawson, H. 2010. ''A Journey Through the Systems Landscape''. London, UK: College Publications, Kings College.
  
Skyttner, L. (2001) General Systems Theory: Ideas and Applications. Singapore: World Scientific Publishing Co. (Pages 53 - 69)
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Martin, J. N. 1997.  ''Systems Engineering Guidebook.''  Boca Raton, FL, USA: CRC Press.
  
Ashby, W R. 1956. Introduction to Cybernetics London; Wiley (chapter 11)
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Skyttner, L. 2001. ''General Systems Theory: Ideas and Applications.'' Singapore: World Scientific Publishing Co., pp. 53-69.
  
Simon, H. A. 1962.  The Architecture of Complexity. Proceedings of the American Philosophical Society, Vol. 106, No. 6. (Dec. 12, 1962), pp. 467-482.
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Simon, H.A. 1962.  "The architecture of complexity," ''Proceedings of the American Philosophical Society'', vol. 106, no. 6, December 12, pp. 467-482.
  
Martin J. N. 1997. Systems Engineering Guidebook. CRC Press, 1997. ISBN 0849378370
+
Simon, H. 1996. ''The Sciences of the Artificial'', 3rd ed. Cambridge, MA, USA: MIT Press.
  
 
===Primary References===
 
===Primary References===
Ackoff, R.L. 1971. [[Towards a System of Systems Concepts]], Management Science, Vol.17 No. 11, USA.
+
Ackoff, R.L. 1971. "[[Towards a System of Systems Concept|Towards a system of systems concept]]," ''Management Science'', vol. 17, no. 11.  
  
Hitchins, Derek. 2009. [[What are the General Principles Applicable to Systems?]] Insight, 59-63.
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Hitchins, D. 2009. "[[What are the General Principles Applicable to Systems?|What are the general principles applicable to systems?]]" INCOSE ''Insight'', vol. 12, no. 4,pp 59-63.
  
 
===Additional References===
 
===Additional References===
Waring, A. (1996) Practical Systems Thinking. London: International Thomson Business Press (Chapter 1)
+
Edson, R. 2008. ''Systems Thinking. Applied. A Primer''. Arlington, VA, USA: Applied Systems Thinking Institute (ASysT), Analytic Services Inc.
 
 
Edson, Robert. 2008. Systems Thinking. Applied. A Primer. edited by AsysT Institute. Arlington, VA: Analytic Services.
 
 
 
Hitchins, Derek K. 2007. Systems Engineering: A 21st Century Systems Methodology Edited by A. P. Sage, Wiley Series in Systems Engineering and Management. Hoboken, NJ: John Wiley & Sons.
 
  
Jackson, Scott, Derek Hitchins, and Howard Eisner. 2010. What is the Systems Approach? INCOSE Insight, April, 41-43.
+
Jackson, S., D. Hitchins, and H. Eisner. 2010. "What is the systems approach?" INCOSE ''Insight'', vol. 13, no. 1, April, , pp. 41-43.  
  
Lawson, Harold. 2010. A Journey Through the Systems Landscape. London: College  Publications, Kings College.
+
Waring, A. 1996. "Chapter 1," in ''Practical Systems Thinking''. London, UK: International Thomson Business Press.
  
===Article Discussion===
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----
Peter Checkland is an INCOSE Pioneer and one of the  most respected authorities on systems theory.
 
  
Derek Hitchins is an INCOSE Fellow and an author of several books on systems theory and systems engineering. He is a respected authority on both subjects.]]]
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<center>[[What is Systems Thinking?|< Previous Article]] | [[Systems Thinking|Parent Article]] | [[Principles of Systems Thinking|Next Article >]]</center>
<center>[[System Concepts|<- Previous Article]] | [[System Concepts|Parent Article]] | [[Complexity|Next Article ->]]</center>
 
  
====Review Comments====
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<center>'''SEBoK v. 2.9, released 20 November 2023'''</center>
The followoing are review comments from Sanford Friedenthal on August 16, 2011 in response to Nicole's SEBoK Review Request:
 
*The link from Part II to this section is not direct.
 
*The section uses bold to identify key terms, but these do not appear to be glossary terms. This convention does not seem to be consistent with the rest of the Wiki.
 
*Intro: spell out GST.
 
*Wholeness: The descriptions of the terms absract and concrete are not very clear. (Also, the use of the term abstract and concrete is different than how the terms are used for abstract and physical models in the modeling section)
 
*Survival Behavior: The following statement seems quite controversial “All systems seek to continue to exist”. This should probably be qualified to apply to socio-technical systems and organizations. Engineered Systems do not seek to exist, although the engineers that develop them may.
 
*Goals and Objectives: I question the definition of the term objective.
 
*Function: the term synchronous and asynchronous do not seem to reflect common usage (e.g wait for a reply prior to proceeding)
 
*Control:
 
**Refers to Black box and white box (these terms are in the glossary, but this section does not refer to them)
 
**Need to fix the grammar of the following “The law of requisite variety (Ashby, 1956) states that a control system must have great than or equal to the variety of the system it is controlling.”
 
*Hierarchy, Emergence, and Complexity: Emergence and emergent properties apply more than to just Engineered Systems (which seems to be implied from the wording)
 
*Completeness: I did not follow this section at all
 
*References: Include specific sections in the SE Guidebook
 
  
==Signatures==
 
--[[User:Radcock|Radcock]] 19:20, 15 August 2011 (UTC)
 
 
[[Category:Part 2]][[Category:Topic]]
 
[[Category:Part 2]][[Category:Topic]]
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[[Category:Systems Thinking]]

Latest revision as of 23:19, 18 November 2023


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


This article forms part of the Systems Thinking knowledge area (KA). It describes systems conceptssystems concepts, knowledge that can be used to understand problemsproblems and solutionssolutions to support systems thinking.

The conceptsconcepts below have been synthesized from a number of sources, which are themselves summaries of concepts from other authors. Ackoff (1971) proposed a system of system concepts as part of general system theorygeneral system theory (GST); Skyttner (2001) describes the main GST concepts from a number of systems sciencesystems science authors; Flood and Carlson (1993) give a description of concepts as an overview of systems thinking; Hitchins (2007) relates the concepts to systems engineeringsystems engineering practice; and Lawson (2010) describes a system of system concepts where systems are categorized according to fundamental concepts, types, topologies, focus, complexitycomplexity, and roles.

Wholeness and Interaction

A systemsystem is defined by a set of elementselements which exhibit sufficient cohesioncohesion, or "togetherness," to form a bounded whole (Hitchins 2007; Boardman and Sauser 2008).

According to Hitchins, interaction between elements is the "key" system concept (Hitchins 2009, 60). The focus on interactions and holismholism is a push-back against the perceived reductionistreductionist focus on parts and provides recognition that in complexcomplex systems, the interactions among parts is at least as important as the parts themselves.

An open systemopen system is defined by the interactions between system elementssystem elements within a system boundarysystem boundary and by the interaction between system elements and other systems within an environmentenvironment (see What is a System?). The remaining concepts below apply to open systems.

Regularity

RegularityRegularity is a uniformity or similarity that exists in multiple entities or at multiple times (Bertalanffy 1968). Regularities make science possible and engineeringengineering efficient and effective. Without regularities, we would be forced to consider every natural and artificial system problem and solution as unique. We would have no scientific laws, no categories or taxonomies, and each engineering effort would start from a clean slate.

Similarities and differences exist in any set or population. Every system problem or solution can be regarded as unique, but no problem/solution is in fact entirely unique. The nomothetic approach assumes regularities among entities and investigates what the regularities are. The idiographic approach assumes each entity is unique and investigates the unique qualities of entities, (Bertalanffy 1975).

A very large amount of regularity exists in both natural systems and engineered systemsengineered systems. Patterns of systems thinking capture and exploit that regularity.

State and Behavior

Any quality or property of a system elementsystem element is called an attributeattribute. The statestate of a system is a set of system attributes at a given time. A system event describes any change to theenvironmentenvironment of a system, and hence its state:

  • Static - A single state exists with no events.
  • Dynamic - Multiple possible stable states exist.
  • Homeostatic - System is static but its elements are dynamic. The system maintains its state by internal adjustments.

A stable state is one in which a system will remain until another event occurs.

State can be monitored using state variables, valuesvalues of attributes which indicate the system state. The set of possible values of state variables over time is called the "'state space'". State variables are generally continuous but can be modeled using a finite state model (or "state machine").

Ackoff (1971) considers "change" to be how a system is affected by events, and system behaviorbehavior as the effect a system has upon its environment. A system can

  • react to a request by turning on a light,
  • respond to darkness by deciding to turn on the light, or
  • act to turn on the lights at a fixed time, randomly or with discernible reasoning.

A stable system is one which has one or more stable states within an environment for a range of possible events:

  • Deterministic systems have a one-to-one mapping of state variables to state space, allowing future states to be predicted from past states.
  • Non-Deterministic systems have a many-to-many mapping of state variables; future states cannot be reliably predicted.

The relationship between determinism and system complexity, including the idea of chaoticchaotic systems, is further discussed in the Complexity article.

Survival Behavior

Systems often behave in a manner that allows them to sustain themselves in one or more alternative viable states. Many natural or social systems have this goal, either consciously or as a "self organizing" system, arising from the interaction between elementselements.

EntropyEntropy is the tendency of systems to move towards disorder or disorganization. In physics, entropy is used to describe how organized heat energy is “lost” into the random background energy of the surrounding environment (the 2nd Law of Thermodynamics). A similar effect can be seen in engineered systemsengineered systems. What happens to a building or garden left unused for any time? Entropy can be used as a metaphor for aging, skill fade, obsolescence, misuse, boredom, etc.

"Negentropy" describes the forces working in a system to hold off entropy. HomeostasisHomeostasis is the biological equivalent of this, describing behavior which maintains a "steady state" or "dynamic equilibrium." Examples in nature include human cells, which maintain the same function while replacing their physical content at regular intervals. Again, this can be used as a metaphor for the fight against entropy, e.g. training, discipline, maintenance, etc.

Hitchins (2007) describes the relationship between the viability of a system and the number of connections between its elements. Hitchins's concept of connected variety states that stability of a system increases with its connectivity (both internally and with its environment). (See varietyvariety.)

Goal Seeking Behavior

Some systems have reasons for existence beyond simple survival. Goal seeking is one of the defining characteristics of engineered systemsengineered systems:

  • A goal is a specific outcome which a system can achieve in a specified time
  • An objective is a longer-term outcome which can be achieved through a series of goals.
  • An ideal is an objective which cannot be achieved with any certainty, but for which progress towards the objective has valuevalue.

Systems may be single-goal seeking (perform set tasks), multi-goal seeking (perform related tasks), or reflective (set goals to tackle objectives or ideas). There are two types of goal seeking systems:

  • PurposivePurposive systems have multiple goals with some shared outcome. Such a system can be used to provide pre-determined outcomes within an agreed time period. This system may have some freedom to choose how to achieve the goal. If it has memory, it may develop processesprocesses describing the behaviors needed for defined goals. Most machines or softwaresoftware systems are purposive.
  • PurposefulPurposeful systems are free to determine the goals needed to achieve an outcome. Such a system can be tasked to pursue objectives or ideals over a longer time through a series of goals. Humans and sufficiently complex machines are purposeful.

Control Behavior

CyberneticsCybernetics, the science of controlcontrol, defines two basic control mechanisms:

  • Negative feedback, maintaining system state against set objectives or levels.
  • Positive feedback, forced growth or contraction to new levels.

One of the main concerns of cybernetics is the balance between stability and speed of response. A black-box systemblack-box system view looks at the whole system. Control can only be achieved by carefully balancing inputs with outputs, which reduces speed of response. A white-box systemwhite-box system view considers the system elementssystem elements and their relationships; control mechanisms can be embedded into this structure to provide more responsive control and associated risks to stability.

Another useful control concept is that of a "meta-system", which sits over the system and is responsible for controlling its functions, either as a black-box or white-box. In this case, behavior arises from the combination of system and meta-system.

Control behavior is a trade between:

  • Specialization, the focus of system behavior to exploit particular features of its environment, and
  • FlexibilityFlexibility, the ability of a system to adapt quickly to environmental change.

While some system elements may be optimized for specialization, a temperature sensitive switch, flexibility, or an autonomous human controller, complex systems must strike a balance between the two for best results. This is an example of the concept of dualismdualism, discussed in more detail in Principles of Systems Thinking.

VarietyVariety describes the number of different ways elements can be controlled and is dependent on the different ways in which they can then be combined. The Law of Requisite Variety states that a control system must have at least as much variety as the system it is controlling (Ashby 1956).

Function

Ackoff defines functionsfunctions as outcomes which contribute to goals or objectives. To have a function, a system must be able to provide the outcome in two or more different ways. (This is called equifinality.)

This view of function and behaviorbehavior is common in systems science. In this paradigmparadigm, all system elements have behavior of some kind; however, to be capable of functioning in certain ways requires a certain richness of behaviors.

In most hard systemshard systems approaches, a set of functions are described from the problem statement and then associated with one or more alternative element structuresstructures (Flood and Carson 1993). This process may be repeated until a system componentcomponent (implementable combination of function and structure) has been defined (Martin 1997). Here, function is defined as either a task or activity that must be performed to achieve a desired outcome or as a transformation of inputs to outputs. This transformation may be:

  • Synchronous, a regular interaction with a closely related system, or
  • Asynchronous, an irregular response to a demand from another system that often triggers a set response.

The behavior of the resulting system is then assessed as a combination of function and effectivenesseffectiveness. In this case, behavior is seen as an external property of the system as a whole and is often described as analogous to human or organic behavior (Hitchins 2009).

Hierarchy, Emergence and Complexity

System behavior is related to combinations of element behaviors. Most systems exhibit increasing variety; i.e., they have behavior resulting from the combination of element behaviors. The term "synergy," or weak emergenceemergence, is used to describe the idea that the whole is greater than the sum of the parts. This is generally true; however, it is also possible to get reducing variety, in which the whole function is less than the sum of the parts (Hitchins 2007).

Complexity frequently takes the form of hierarchieshierarchies. Hierarchic systems have some common properties independent of their specific content, and they will evolve far more quickly than non-hierarchic systems of comparable size (Simon 1996). A natural system hierarchy is a consequence of wholeness, with strongly cohesive elements grouping together forming structures which reduce complexity and increase robustnessrobustness (Simon 1962).

EncapsulationEncapsulation is the enclosing of one thing within another. It may also be described as the degree to which it is enclosed. System encapsulation encloses system elements and their interactions from the external environment, and usually involves a system boundary that hides the internal from the external; for example, the internal organs of the human body can be optimized to work effectively within tightly defined conditions because they are protected from extremes of environmental change.

Socio-technical systems form what are known as control hierarchies, with systems at a higher level having some ownership of control over those at lower levels. Hitchins (2009) describes how systems form "preferred patterns" which can be used to enhance the stability of interacting systems hierarchies.

Looking across a hierarchy of systems generally reveals increasing complexity at the higher level, relating to both the structure of the system and how it is used. The term emergenceemergence describes behaviors emerging across a complex system hierarchy.

Effectiveness, Adaptation and Learning

Systems effectivenesseffectiveness is a measure of the system's ability to perform the functions necessary to achieve goals or objectives. Ackoff (1971) defines this as the product of the number of combinations of behavior to reach a function and the efficiency of each combination.

Hitchins (2007) describes effectiveness as a combination of performance (how well a function is done in ideal conditions), availability (how often the function is there when needed), and survivability (how likely is it that the system will be able to use the function fully).

System elements and their environments change in a positive, neutral or negative way in individual situations. An adaptiveadaptive system is one that is able to change itself or its environment if its effectiveness is insufficient to achieve its current or future objectives. Ackoff (1971) defines four types of adaptation, changing the environment or the system in response to internal or external factors.

A system may also learn, improving its effectiveness over time without any change in state or goal.

References

Works Cited

Ackoff, R.L. 1971. "Towards a system of systems concepts," Management Science, vol. 17, no. 11.

Ackoff, R. 1979. "The future of operational research is past," Journal of the Operational Research Society, vol. 30, no. 2, pp. 93–104, Pergamon Press.

Ashby, W R. 1956. "Chapter 11," in Introduction to Cybernetics. London, UK: Wiley.

Bertalanffy, L. von. 1968. General System Theory: Foundations, Development, Applications, Revised ed. New York, NY, USA: Braziller.

Bertalanffy, L. von. 1975. Perspectives on General System Theory. E. Taschdjian, ed. New York, NY, USA: George Braziller.

Boardman, J. and B. Sauser. 2008. Systems Thinking: Coping with 21st Century Problems. Boca Raton, FL, USA: Taylor & Francis.

Flood, R.L. and E.R. Carson. 1993. Dealing with Complexity: An Introduction to the Theory and Application of Systems Science. New York, NY, USA: Plenum Press.

Hitchins, D. 2007. Systems Engineering: A 21st Century Systems Methodology. Hoboken, NJ, USA: John Wiley and Sons.

Hitchins, D. 2009. "What are the general principles applicable to systems?" INCOSE Insight, vol. 12, no. 4, pp. 59-63.

Lawson, H. 2010. A Journey Through the Systems Landscape. London, UK: College Publications, Kings College.

Martin, J. N. 1997. Systems Engineering Guidebook. Boca Raton, FL, USA: CRC Press.

Skyttner, L. 2001. General Systems Theory: Ideas and Applications. Singapore: World Scientific Publishing Co., pp. 53-69.

Simon, H.A. 1962. "The architecture of complexity," Proceedings of the American Philosophical Society, vol. 106, no. 6, December 12, pp. 467-482.

Simon, H. 1996. The Sciences of the Artificial, 3rd ed. Cambridge, MA, USA: MIT Press.

Primary References

Ackoff, R.L. 1971. "Towards a system of systems concept," Management Science, vol. 17, no. 11.

Hitchins, D. 2009. "What are the general principles applicable to systems?" INCOSE Insight, vol. 12, no. 4,pp 59-63.

Additional References

Edson, R. 2008. Systems Thinking. Applied. A Primer. Arlington, VA, USA: Applied Systems Thinking Institute (ASysT), Analytic Services Inc.

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

Waring, A. 1996. "Chapter 1," in Practical Systems Thinking. London, UK: International Thomson Business Press.


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