Synthesizing Possible Solutions
This topic is part of the Systems Approach Applied to Engineered Systems knowledge area (KA). It describes knowledge related to the synthesis of possible solution options in response to the problem situations described by activities from Identifying and Understanding Problems and Opportunities topic. The solution options proposed by the synthesis activities will form the starting point for the Analysis and Selection between Alternative Solutions. Any of the activities described below may also need to be considered concurrently with other activities in the systems approach at a particular point in the life of a system-of-interest (SoI).
The activities described below should be considered in the 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 elements of systems engineering (SE).
- 1 Synthesis Overview
- 2 Problem or Opportunity Context
- 3 Synthesis Activities
- 4 Defining the System-of-Interest
- 5 References
System synthesis is an activity within the systems approach that is used to describe one or more system solutions based upon a problem context for the life cycle of the system to:
- Define options for a SoI with the required properties and behavior for an identified problem or opportunity context.
- Provide solution options relevant to the SoI in its intended environment, such that the options can be assessed to be potentially realizable within a prescribed time limit, cost, and risk described in the problem context.
- Assess the properties and behavior of each candidate solution in its wider system context.
The iterative activity of system synthesis develops possible solutions and may make some overall judgment regarding the feasibility of said solutions. The detailed judgment on whether a solution is suitable for a given iteration of the systems approach is made using the Analysis and Selection between Alternative Solutions activities.
Essential to synthesis is the concept of holism, according to Hitchins (Hitchins 2009), and states that a system must be considered as a whole and not simply as a collection of its elements. The holism of any potential solution system requires that the behavior of the whole be determined by addressing a system within an intended environment and not simply the accumulation of the properties of the elements. The latter process is known as reductionism and is the opposite of holism, which Hitchins (Hitchins 2009, 60) describes as the notion that “the properties, capabilities, and behavior of a system derive from its parts, from interactions between those parts, and from interactions with other systems.”
When the system is considered as a whole, properties called emergent properties often appear (see Emergence). These properties are often difficult to predict from the properties of the elements alone. They must be evaluated within the systems approach to determine the complete set of performance levels of the system. According to Jackson (Jackson 2010), these properties can be considered in the design of a system, but to do so, an iterative approach is required.
In complex systems, individual elements will adapt to the behavior of the other elements and to the system as a whole. The entire collection of elements will behave as an organic whole. Therefore, the entire synthesis activity, particularly in complex systems, must itself be adaptive.
Hence, synthesis is often not a one-time process of solution design, but is used in combination with problem understanding and solution analysis 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).
Problem or Opportunity Context
System synthesis needs the problem or opportunity that the system is intended to address to have already been identified and described and for non-trivial systems, the problem or opportunity needs to be identified and understood concurrently with solution synthesis activities.
As discussed in Identifying and Understanding Problems and Opportunities, the systems approach should not consider strictly soft or hard situations. In general, the application of the systems approach, with a focus on engineered system contexts, will lead to hard system contexts in which an identified SoI and required outcome be defined. Even in these cases, a soft context view of the SoI context will help ensure wider stakeholder concerns are considered.
The problem context should include some boundaries on the cost, time to deployment, time in use, and operational effectiveness needed by stakeholders. In general, the goal is not to synthesize the perfect solution to a problem, but rather to find the best available solution for the agreed version of the problem.
The following activities provide an outline for defining the SoI: grouping of elements, identification of the interactions among the elements, identification of interfaces between elements, identification of external interfaces to the SoI boundary and common sub-elements within the SoI boundary.
The activities of systems synthesis are built on the idea of a balanced reduction vs. holism approach as discussed in What is Systems Thinking? topic. It is necessary to divide system elements and functions to create a description of the SoI which is realizable, either through combinations of available elements or through the design and construction of new elements. However, if the system is simply decomposed into smaller and smaller elements, the holistic nature of systems will make it more and more difficult to predict the function and behavior of the whole. Thus, synthesis progresses through activities that divide, group, and allocate elements, and then assesses the complete system’s properties in context relevant to the user need the SoI will fulfill. Hence, synthesis occurs over the entire life cycle of the system as the system and its environment change.
Identification of the Boundary of a System
Establishing the boundary of a system is essential to synthesis, the determination of the system's interaction with its environment and with other systems, and the extent of the SoI. Buede (Buede 2009, 1102) provides a comprehensive discussion of the importance of, and methods of, defining the boundary of a system in a SE context.
Identification of the Functions of the System
The function of a system at a given level of abstraction is critical to synthesis since the primary goal of the synthesis activity is to propose realizable system descriptions which can provide a given function. The function of a system is distinct from its behavior as it describes what the system can be used for or is asked to do in a larger system context.
Buede (Buede 2009, 1091-1126) provides a comprehensive description of functional analysis in a SE context.
Identification of the Elements of a System
System synthesis calls for the identification of the elements of a system. Typical elements of an Engineered System Context may be physical, conceptual, or processes. Physical elements may be hardware, software, or humans. Conceptual elements may be ideas, plans, concepts, or hypotheses. Processes may be mental, mental-motor (writing, drawing, etc.), mechanical, or electronic (Blanchard and Fabrycky 2006, 7).
In addition to the elements of the system under consideration (i.e., a SoI), ISO 15288 (ISO/IEC/IEEE 15288 2015) also calls for the identification of the enabling systems. These are systems (or services) utilized at various stages in the life cycle, e.g., development, utilization or support stages, to facilitate the SoI in achieving its objectives.
Today's systems often include existing elements. It is rare to find a true "greenfield" system, in which the developers can specify and implement all new elements from scratch. "Brownfield" systems, wherein legacy elements constrain the system structure, capabilities, technology choices, and other aspects of implementation, are much more typical (Boehm 2009).
Division of System Elements
System synthesis may require elements to be divided into smaller elements. The division of elements into smaller elements allows the systems to be grouped and leads to the SE concept of physical architecture, as described by Levin (Levin 2009, 493-495). Each layer of division leads to another layer of the hierarchical view of a system. As Levin points out, there are many ways to depict the physical architecture, including the use of wiring diagrams, block diagrams, etc. All of these views depend on arranging the elements and dividing them into smaller elements. According to the principle of recursion, these decomposed elements are either terminal elements, or are able to be further decomposed. The hierarchical view does not imply a top-down analytical approach to defining a system. It is simply a view. In the systems approach, levels of the hierarchy are defined and considered recursively with one level forming the context for the next.
Grouping of System Elements
System synthesis may require that elements be grouped. This leads to the identification of the sub-systems that are essential to the definition of a system. Synthesis determines how a system may be partitioned and how each sub-system fits and functions within the whole system. The largest group is the SoI, also called the relevant system by Checkland (Checkland 1999, 166). According to Hitchins, some of the properties of a SoI are as follows: the SoI is open and dynamic, the SoI interacts with other systems, and the SoI contains sub-systems (Hitchins 2009, 61). The SoI is brought together through the concept of synthesis.
Identification of the Interactions among System Elements
System synthesis may require the identification of the interactions among system elements. These interactions lead to the SE process of interface analysis. Integral to this aspect is the principle of interactions. Interactions occur both with other system elements as well as with external elements and the environment. In a systems approach, interfaces have both a technical and managerial importance. Managerial aspects include the contracts between interfacing organizations. Technical aspects include the properties of the physical and functional interfaces. Browning provides a list of desirable characteristics of both technical and managerial interface characteristics (Browning 2009, 1418-1419) .
System synthesis will include activities to understand the properties of system elements, the structure of proposed system solutions, and the resultant behavior of the composed system. A number of system concepts for describing system behavior are discussed in Concepts of Systems Thinking topic. It should be noted that in order to fully understand a system’s behavior, we must consider the full range of environments in which it might be placed and its allowable state in each. According to Page, in complex systems, the individual elements of the system are characterized by properties which enhance the systems as a whole, such as their adaptability (Page 2009).
Defining the System-of-Interest
Flood and Carson provide two ways to identify system boundaries: a bottom-up, or structural approach, which starts with significant system elements and builds out, and a top down, or behavioral approach, in which major systems needed to fulfill a goal are identified and then the work flows downward (Flood and Carson 1993). They identify a number of rules proposed by Beishon (Beishon 1980) and Jones (Jones 1982) to help in the selection of the best approach.
In either case, the ways in which system elements are refined, grouped, and allocated must be driven towards the synthesis of a realizable system solution description. A realizable solution must consider elements that are either already available, can be created from existing system elements, or are themselves described as system contexts which will need to be synthesized at a future point. In the third case, it is one of the outcomes of the Analysis and Selection between Alternative Solutions activities that is used to assess the risk that a given element may not be able to be synthesized in the required time limit or cost budget.
A top down approach might start with a system boundary and an overall description of system functions. Through the repeated application of element identification, division, grouping, and allocation of functions, a complete description of the elements needed for the SoI can be defined. In this case, the choice of system elements and allocation of functions may be guided by pre-defined ways of solving a given problem or by identified system patterns; both can support as well as insert bias into the synthesis. For example, one might start with the need to provide energy to a new housing project and propose solution options based around connections to an existing power grid, local power generators, renewable energy sources, increased energy efficiency, etc.
The iterative nature of analysis also reflects the need to change the solution as the life cycle progresses and changes the system's environment; thereby, possibly changing what a "best" solution is.
A bottom up approach starts with major elements and interactions. Again, division, grouping, and identification allows for the construction of a full system description that is capable of providing all the necessary functions, at which point the final SoI boundary can be set. In this case, the choice of system elements and groupings will be driven by the goal of ensuring that the major system elements can be formed together into a viable system whole. For example, there may be a need to replace an existing delivery vehicle and produce solution options that consider vehicle ownership/leasing, driver training, petrol, diesel or electric fuel, etc.
The systems approach aspect of synthesis leads to SE terms such as “design” and “development.” Wasson describes synthesis from a SE point of view (Wasson 2006, 390-690). White provides a comprehensive discussion of methods of achieving design synthesis (White 2009, 512-515). The systems approach treats synthesis at the abstract level while the SE process definitions provide the concrete steps.
The SoI brings together elements, sub-systems and systems through the concept of synthesis to identify a solution option.
Synthesis of possible solutions may result in the development of artifacts documenting the synthesis itself and provide the basis for analysis and selection between alternative solutions. These artifacts are dynamic and will change as the SoI changes its environment throughout the system life cycle.
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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.
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