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Chapter 2: System Thinking
Terms in this set (29)
thinking about a question, circumstance, or problem explicitly as a system—a set of interrelated entities.
a set of entities and their relationships, whose functionality is greater than the sum of the individual entities.
some- thing that is, or has the potential to be, exchanged.
an abstract description of the entities of a system and the relation- ships between those entities.
functionality is greater than the sum of the individual entities.
an emergent property; how well a system operates or executes its function(s).
the other attributes of operation that emerge from a system, such as reliability, maintainability, operability, safety, and robustness.
Principle of Emergence
• The interaction of entities leads to emergence. Emergence refers to what appears, materializes, or surfaces when a system operates. It is this emergence that can give systems added value.
• As a consequence of emergence, change propagates in unpredictable ways.
• It is difficult to predict how a change in one entity will influence the emergent properties.
• System success occurs when the anticipated properties emerge. System failure occurs when the anticipated emergent properties fail to appear or when unanticipated undesirable emergent properties appear.
Task 1: Identify the system's form and function
• All systems have form (what the system is) and function (what the system does). The form is the instrument of the function.
• Function further breaks down into process (the transformation) and the operand (the object that is transformed or whose state is changed).
• The primary function of most human-built systems is usually clear.
• The primary function of evolved systems is more difficult to discern and is often
subject to interpretation.
• The proposed representation of a system (instrument form-process-operand) very
closely resembles the deep structure of natural language (noun-verb-object).
What the system "is"; it is the physical or informational embodiment that exists or has the potential to exist.
What the system "does"; it is the activities, operations, and transformations that cause, create, or contribute to performance. Function is the action for which a thing exists or is employed.
Function's two subsets:
processes and operands
The process is the part of function that is pure action or transformation, and thus it is the part that changes the state of the operand.
the thing whose state is changed by that process.
Task 2: Identify the entities of a system, their form, their function, and the system boundary and context.
• All systems are composed of entities, which have form and function and are them- selves likely to be systems.
• Defining the composition of the system as entities is easy for a system made up of distinct entities, is moderately difficult for a modular system, and is quite difficult for integral systems.
• Thinking holistically helps to identify all of the entities that might be important to represent in the system, but it often yields too many entities to usefully consider.
• Focus helps to reduce the entities to those that are consequential to consider at that moment, but the set may change with time and activity.
• Creating abstractions helps bring to the surface the essential details of an entity, while hiding the rest of the complexity.
• Defining a boundary separates the system from the context.
Breaking the SYSTEM into smaller pieces.
Collecting pieces into the form of the system
Breaking the FUNCTION into constituents (different than decomposition)
Emergence occurs when:
when the functions of the ENTITIES combine to produce the function of the system
System generalization comment:
All systems are composed of entities that are also systems, and all systems are entities of larger systems.
Defining entities and boundaries of a system includes (5):
• Defining the initial decomposition into entities
• Identifying the potential entities using holistic thinking
• Winnowing down to the consequential entities using focus
• Creating abstractions for the entities
• Defining the boundary of the system, and separating the system from context
Defining the Initial Decomposition into Entities
Are the entities distinct (a group of people), modular (parts of a circuit), or integral (steering mechanisms of a car)?
Identifying the potential entities using holistic thinking
To think holistically is to encompass all aspects of the system at hand, taking into account the influences and consequences of anything that might interact with the system.
Winnowing down to the consequential entities using focus
The number of identifiable issues that will influence a system at any point is beyond one's ability to understand. One must identify the most critical and consequential issues, and focus on them.
Create or Recognize Abstractions for the Entities
• Create abstractions of form and function with the important information represented on the surface, and with less important details concealed.
• Create abstractions that allow for representation of appropriate relationships (see Section 2.5).
• Create abstractions at the right level of decomposition or aggregation.
• Create the minimum number of abstractions that will effectively represent the
aspects of the system at hand.
Define the Boundary of the System, and Separate It from Context
• Including the entities to be analyzed (if the goal is understanding)
• Including what is necessary to create the design (if the goal is design)
• Including what we are responsible for implementing and operating (if the goal is
delivery of value)
• Formal boundaries, established by law, contract, or other legal regime
• Traditions or conventions that distinguish the system from context
• Interface definitions or standards that we must respect, including supplier relationships
Task 3: Identify the Relationships among the Entities
• Fundamental to the definition of a system is the existence of relationships among the entities, which can be formal (they exist or could exist—structure) or functional (they do something—interactions).
• In general, some of the entities of a system will also have both formal and functional relationships with context entities outside the system; such relationships occur across external interfaces.
• Formal and functional interactions can be effectively represented by either relation- ship diagrams or N-Squared tables.
Formal and functional relationships can exist across the boundary of the system, between entities in the system and its context.
Task 4: Emergence
• Emergence occurs when the function of the entities and their functional interaction combine to produce a new functionality, which is more than the "sum of the parts."
• System success and system failure often hinge on emergence.
• Emergence can be predicted a priori by relying on precedent, experimentation, and modeling. For unprecedented systems for which experimentation and modeling are not easy, humans must reason about emergence based on available information.
• Emergence depends on the function of the entities enabled by form, and on the functional relationships enabled by the formal relationships.
• It is the property of emergence that gives systems their power and also creates the challenges in understanding and predicting them.
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