Difference between revisions of "System Definition"

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[[System Definition (glossary)|System definition]] activities are conducted to create and describe in detail a system to satisfy an identified need. The activities are grouped and described as generic processes that are performed concurrently, iteratively and recursively depending on the selected [[Life Cycle Models|life cycle model]], see [[Applying Life Cycle Processes]] for further discussion of the relationships between process and life cycle model. The system definition processes consist of system requirements definition, system architecture definition, system design definition and system analysis. For creation purpose, the architecture definition of the system may include the development of related logical architecture models and physical architecture models. During and/or at the end of any iteration, gap analysis is performed to ensure that all system requirements have been mapped to the architecture and design.
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'''''Lead Authors:''''' ''Alan Faisandier, Garry Roedler'', '''''Contributing Author:''''' ''Rick Adcock''
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{{Term|System Definition (glossary)|System definition}} activities are conducted to create and describe in detail a {{Term|System-of-Interest (glossary)|system-of-interest}} (SoI) to satisfy an identified need. The activities are grouped and described as generic processes. which consist of system requirements definition, system architecture definition, system design definition and system analysis. The architecture definition of the system may include the development of related logical architecture models and physical architecture models. During and/or at the end of any iteration, gap analysis is performed to ensure that all system requirements have been mapped to the architecture and design.
  
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System definition activities build on the artifacts and decisions from [[Concept Definition (glossary) | concept definition]], primarily the articulation of the [[Mission (glossary) | mission]] of the [[System-of-Interest (glossary)|system-of-interest]] (SoI), the [[Stakeholder Requirement (glossary)|needs and requirements of stakeholders]], and preliminary operational concepts.  The products of system definition activities (system requirements, architecture and design) are inputs to [[System Realization (glossary) |system realization]]. The specific activities and sequence of system definition activities will be dependent upon the type of life cycle model being utilized.
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System definition activities build on the artifacts and decisions from {{Term|Concept Definition (glossary)|concept definition}}, primarily the articulation of the {{Term|Mission (glossary)|mission}} of the (SoI), the {{Term|Stakeholder Requirement (glossary)|needs and requirements of stakeholders}}, and preliminary operational concepts.  See [[Life Cycle Processes and Enterprise Need]] for further detail on the transformation of needs and requirements from the business or enterprise and stakeholder levels of abstraction addressed in concept definition to the system and system element level of abstraction addressed in system definition.
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The products of system definition activities (system requirements, architecture and design) are inputs to {{Term|System Realization (glossary)|system realization}}.  
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The specific activities and sequence of system definition activities and their involvement with the life cycle activities of any system, and in particular the close integration with concept definition and system realization activities, will be dependent upon the type of {{Term|Life Cycle Model (glossary)|life cycle model}} being utilized. See [[Applying Life Cycle Processes]] for further discussion of the concurrent, iterative and recursive nature of these relationships.
  
 
==Topics==
 
==Topics==
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*[[System Requirements]]
 
*[[System Requirements]]
 
* [[System Architecture]]
 
* [[System Architecture]]
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*[[Logical Architecture Development]]
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*[[Logical Architecture Model Development]]
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*[[Physical Architecture Development]]
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*[[Physical Architecture Model Development]]
 
* [[System Design]]
 
* [[System Design]]
 
*[[System Analysis]]
 
*[[System Analysis]]
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==System Views and System Elements ==
 
==System Views and System Elements ==
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An [[Engineered System (glossary)]] solution to a defined concept includes a defined set of engineering elements, characteristics, and  properties. These elements are grouped in two ways:  
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An {{Term|Engineered System (glossary)}} solution to a defined concept includes a set of engineering elements, characteristics, and  properties. These elements are grouped in two ways:  
 
* Needs and requirements views
 
* Needs and requirements views
 
* Architecture and design views
 
* Architecture and design views
  
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Architecture views include the identification of the boundary and interfaces of a system-of-interest (SoI), which may then be further refined as a collection of [[System Element (glossary)|system elements]] and their relationships.
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Architecture views include the identification of the boundary and interfaces of a {{Term|System-of-Interest (glossary)|system-of-interest (SoI)}}, which may then be further refined as a collection of {{Term|System Element (glossary)|system elements}} and their relationships.
  
 
===Needs and Requirements Views===
 
===Needs and Requirements Views===
  
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Requirements provide an overall view of the [[Purpose (glossary)|purpose]] and [[Mission (glossary)|mission]] which the system as a whole is intended to satisfy, as well as a technology-independent view of that the system solutions(s) should do. They are conventionally organized into two types:
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Requirements provide an overall view of the {{Term|Purpose (glossary)|purpose}} and {{Term|Mission (glossary)|mission}} which the system as a whole is intended to satisfy, as well as a technology-independent view of that the system solutions(s) should do. They are conventionally organized into two types:
  
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*Business or mission requirements and [[Stakeholder Requirement (glossary)|Stakeholder requirements]] are defined and discussed in the [[Concept Definition]] KA.
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*Business or mission requirements and {{Term|Stakeholder Requirement (glossary)|Stakeholder requirements}} are defined and discussed in the [[Concept Definition]] KA.
  
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*[[System Requirement (glossary)|System requirements]], which describe the functions which the system as a whole should fulfill in order to satisfy the stakeholder requirements and are expressed in an appropriate set of views, and non-functional requirements expressing the levels of safety, security, reliability, etc., which are called for. These collectively form the basis for [[Verification (glossary)|verification]] later in the life cycle.
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*{{Term|System Requirement (glossary)|System requirements}}, which describe the functions which the system as a whole should fulfill in order to satisfy the stakeholder requirements and are expressed in an appropriate set of views, and non-functional requirements expressing the levels of safety, security, reliability, etc., which are called for. These collectively form the basis for {{Term|Verification (glossary)|verification}} later in the life cycle.
  
 
System requirements and stakeholder requirements are closely related. Neither can be considered complete until consistency between the two has been achieved, as demonstrated by traceability, for which a number of iterations may be needed.
 
System requirements and stakeholder requirements are closely related. Neither can be considered complete until consistency between the two has been achieved, as demonstrated by traceability, for which a number of iterations may be needed.
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===Architecture and Design Views===
 
===Architecture and Design Views===
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A system is one solution that could address/answer a problem or an opportunity (represented through requirements views); the solution may be more or less complex. A complex solution cannot be comprehended with a single view or model, because of the number of characteristics or properties of the solution. The characteristics are structured as types or entities; types are related to each other. An instantiation of the set of types can be understood as THE architecture of the system. The majority of interpretations of system architecture are based on the fairly intangible notion of structure. Therefore, the system architecture and design is formally represented with sets of types or entities such as functions, interfaces, resource flow items, information elements, physical elements, nodes, links, etc. These entities may possess attributes/characteristics such as dimensions, environmental resilience, availability, reliability, learnability, execution efficiency, etc. The entities are interrelated by the means of relationships and are generally grouped into sets to represent views/models of the system architecture and design.  
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A given engineered system is one solution that could address/answer a problem or an opportunity (represented through requirements views); the solution may be more or less {{Term|Complexity (glossary)|complex}}. A complex solution cannot be comprehended with a single view or model, because of the characteristics or properties of the problem/solution (see system [[complexity]]). The characteristics are structured as types or entities; types are related to each other. An instantiation of the set of types can be understood as THE architecture of the system. The majority of interpretations of system architecture are based on the fairly intangible notion of structure. Therefore, the system architecture and design is formally represented with sets of types or entities such as functions, interfaces, resource flow items, information elements, physical elements, nodes, links, etc. These entities may possess attributes/characteristics such as dimensions, environmental resilience, availability, reliability, learnability, execution efficiency, etc. The entities are interrelated by the means of relationships and are generally grouped into sets to represent views/models of the system architecture and design.  
  
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Viewpoints and views are sometimes specified in architecture frameworks such as Zachman (1987), DoDAF (2010), MoDAF (n.d.), The Open Group Architecture Framework (TOGAF), etc. Views are usually generated from models. Many systems engineering practices use logical and physical views for modeling the system architecture and design.
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{{Term|Viewpoint (glossary)|Viewpoints}} and {{Term|View (glossary)|views}} are sometimes specified in {{Term|Architecture Framework (glossary)|architecture frameworks}}. Views are usually generated from models. Many systems engineering practices use logical and physical views for modeling the system architecture and design.
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* The '''[[Logical Architecture (glossary)|logical view of the architecture]]''' supports the logical operation of the system all along its life cycle, and may include functional, behavioral, and temporal views/models. Operational scenarios refine the mission into a collection of [[Function (glossary)|functions]] and dynamic structures that describe how the mission is performed (behavior).
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* The '''{{Term|Logical Architecture (glossary)|logical view of the architecture}}''' supports the logical operation of the system all along its life cycle, and may include functional, behavioral, and temporal views/models. Operational scenarios refine the mission into a collection of {{Term|Function (glossary)|functions}} and dynamic structures that describe how the mission is performed (behavior).
  
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* The '''[[Physical Architecture (glossary)|physical view of the architecture]]''' is a set of [[System Element (glossary)|system elements]] performing the functions of the system. Those system elements can be either material or immaterial (e.g., equipment made of hardware, software and/or human roles).
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* The '''{{Term|Physical Architecture (glossary)|physical view of the architecture}}''' is a set of {{Term|System Element (glossary)|system elements}} performing the functions of the system. Those system elements can be either material or immaterial (e.g., equipment made of hardware, software and/or human roles).
  
 
The boundary of the system architecture depends on what engineers include within the scope of the SoI and outside of it.  This decision marks the transition from the characterization of the problem context to the beginnings of solution definition.
 
The boundary of the system architecture depends on what engineers include within the scope of the SoI and outside of it.  This decision marks the transition from the characterization of the problem context to the beginnings of solution definition.
  
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Facing the potential number of system elements that constitute the physical architecture, sets of system elements can be grouped to form systems. The decomposition of the SoI (highest level) may include the decomposition of several layers of systems (intermediate levels of systems) until technological system elements (lowest level) are defined. Any layer of the decomposition may include systems and non-decomposable technological system elements.
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Facing the potential number of system elements that constitute the physical architecture, sets of system elements can be grouped to form systems. The decomposition of the SoI (highest level) may include the decomposition of several layers of systems (intermediate levels of systems) until technological system elements (lowest level) are defined. Any layer of the decomposition may include systems and non-decomposable technological system elements. The relationship between each layer is {{Term|Recursion (glossary)|recursive}}; as a system element is also an engineered system it can be characterized in its turn using the previous views in its own context.  
  
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Because a system element is primarily an engineered system, it can be characterized in its turn using the previous views in its own context. The notion of system as described and defined here is recursive, see the discussion of systems and engineered system contexts in [[What is a System?]] article.  
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The logical and physical representations of the system architecture are mapped onto each other. The interactions between system elements are defined by interfaces whose complexity strongly depends on the way the system architecture and design is defined. The relationships between the outputs of concept definition and the system solution, as well as the range of other views of a system that are available to describe a more complete set of characteristics between the system elements are discussed further in the [[Logical Architecture Model Development]] and [[Physical Architecture Model Development]] sections of system definition.
  
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The logical and physical representations of the system architecture are mapped onto each other. The interactions between system elements are defined by interfaces whose complexity strongly depends on the way the system architecture and design is defined.  The relationships between the outputs of concept definition and the system solution, as well as the range of other views of a system that are available to describe a more complete set of characteristics between the system elements are discussed further in the [[Logical Architecture Development]] and [[Physical Architecture Development]] sections of the KA.
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==System Synthesis and Decomposition==
  
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==Top-Down and Recursive Approach to System Decomposition==
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System definition is managed through methodical {{Term|Synthesis (glossary)|synthesis}} of the SoI into systems and system elements.  Solution synthesis may be top down or bottom up, as discussed in [[Synthesizing Possible Solutions]].  However it is done, as the system architecture definition advances, a decomposition of systems and system elements emerges, this forms a system breakdown structure (SBS). For project management purposes, every system of the SBS may be included in a ''building block'', a notion introduced in (ANSI/EIA 1998), also called ''system blocks''. 
  
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System definition is managed through methodical top-down decomposition of the SoI into systems and system elements.  As the system architecture definition advances, emerging systems and system elements form a system breakdown structure (SBS). For project management purposes, every system of the SBS may be included in a ''building block'', a notion introduced in (ANSI/EIA 1998), also called ''system block''. 
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{{Term|Stakeholder Requirement (glossary)|Stakeholder requirements}} and {{Term|System Requirement (glossary)|system requirements}} exist at all layers of the SBS. In ISO/IEC/IEEE 29148 ''Systems and software engineering - Requirements Engineering ''(ISO 2011), these layers are known as levels of abstraction. Along with systematically introducing layers of systems, the architecture and design process manages the transformation of the [[System Requirements|system requirements]] through levels of abstraction.  Figure 1 illustrates this approach.
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[[Stakeholder Requirement (glossary)|Stakeholder requirements]] and [[System Requirement (glossary)|system requirements]] exist at all layers of the SBS. In ISO/IEC/IEEE (2011), these layers are known as levels of abstraction. Along with systematically introducing layers of systems, the architecture and design process manages the transformation of the [[System Requirements|system requirements]] through levels of abstraction.  Figure 1 illustrates this approach.
 
  
 
[[File:SEBoKv05_KA-SystDef_Top-down_development_of_design_and_requirements.png|thumb|center|500px|center|'''Figure 1. Top-down Development of Architecture and Design, and Requirements (Faisandier 2012).''' Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.]]
 
[[File:SEBoKv05_KA-SystDef_Top-down_development_of_design_and_requirements.png|thumb|center|500px|center|'''Figure 1. Top-down Development of Architecture and Design, and Requirements (Faisandier 2012).''' Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.]]
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* At the SoI level, the system architecture is developed which serves to identify systems and system elements and establishes how they operate together to address the SoI requirements.  
 
* At the SoI level, the system architecture is developed which serves to identify systems and system elements and establishes how they operate together to address the SoI requirements.  
  
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This approach is applied recursively for each level of abstraction/decomposition recognizing that the same generic processes are applied at multiple levels of abstraction. Figure 2 below portrays the engineering that occurs in each system block. As necessary, system elements are defined through sets of system element requirements, which become inputs to other system blocks (''level n+1''). The approach is then recursively applied using the system definition processes.
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This approach is applied recursively for each level of abstraction/decomposition recognizing that the same generic processes are applied at multiple levels of abstraction. At any level of this decomposition one or more solution options may be presented as system architectures.  The process by which the solution which best fits the system requirements, associated stakeholder needs and wider life cycle concerns is selected and justified is discussed in the [[System Analysis]] process.
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Figure 2 below portrays the engineering that occurs in each system block. As necessary, system elements are defined through sets of system element requirements, which become inputs to other system blocks (''level n+1''). The approach is then recursively applied using the system definition processes.
  
 
[[File:Recursive_Instantiation_of_Def_Process_AF_071112.png|thumb|center|700px|center|'''Figure 2. Recursive Instantiation of Definition Processes (Faisandier 2012).''' Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.]]
 
[[File:Recursive_Instantiation_of_Def_Process_AF_071112.png|thumb|center|700px|center|'''Figure 2. Recursive Instantiation of Definition Processes (Faisandier 2012).''' Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.]]
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At the ''n+1'' level, the systems or system elements may also collect other stakeholder requirements that are directly pertinent to this level of architecture and design. Processes within each system are generic, but unique in local purpose, scope and context.
 
At the ''n+1'' level, the systems or system elements may also collect other stakeholder requirements that are directly pertinent to this level of architecture and design. Processes within each system are generic, but unique in local purpose, scope and context.
  
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See the articles [[Applying Life Cycle Processes]] for a discussion of the iterative and recursive application of system requirements and architecture processes, and [[Life Cycle Processes and Enterprise Need]] for further detail on the transformation of needs and requirements from the business or enterprise and stakeholder levels of abstraction addressed in Concept Definition to the system and system element level of abstraction addressed in System Definition.
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See [[Applying Life Cycle Processes]] for a discussion of the iterative and recursive application of system requirements and architecture processes, and [[Life Cycle Processes and Enterprise Need]] for further detail on the transformation of needs and requirements to system and system element levels of abstraction.
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==System Design==
 
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In industrial practices, the term ''design'' is often used to mean both [[Architecture (glossary)]] and [[Design (glossary)]] as defined in the SEBoK. In the recent past, professionals used the term ''design'' when they dealt with simpler technological products - ones that do not include several different and interconnected technological components such as hardware, software, operators, services, etc. In the development of new multi-technology products and services, professionals have recognized the usefulness of the notion of ''system'' in dealing with [[Complexity (glossary)]] (interconnections level, multi-techno, emergence, etc.).  
 
  
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It was due to complexity that structuring the elements that comprise a system became necessary. This structure explains the functional, behavioral, temporal, physical, and other aspects of a system as previously described. Practitioners found the term ''structure'' inadequate to describe all of these aspects of a system. The terms ''architecture'' and ''architectural design'' have been used for approximately 30 years, especially in software intensive systems and other domains, such as the space industry. The set of different types and interrelated structures can be understood as the architecture of the system.
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The different aspects of how {{Term|Systems Thinking (glossary)|systems thinking}} is applicable to system definition are discussed in SEBoK Part 2. In particular, see discussion of the recursive nature of systems and engineered system contexts in [[Engineered System Context]]; the contrast between top-down and bottom up approaches in [[Synthesizing Possible Solutions]] and the role of solution architecture options and selection in [[Analysis and Selection between Alternative Solutions]].  
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The trend today is to consider system architecture and system design as different sets of activities. Attempts are made to define separate concurrent processes, but they are strongly intertwined:
 
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* System design includes activities to conceive a system that answers a specific, intended purpose, using principles and concepts; it includes assessments and decisions to select elements that compose the system, fit the architecture of the system, and comply with traded-off system requirements. It is the complete set of detailed models, properties, and/or characteristics described into a form suitable for implementation.
 
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* System architecture is more abstract, conceptualization-oriented, global, and focused on mission success and on high level structure in (sub)systems. It may also be applied to more than one system, in some cases forming the common structure, pattern, and set of requirements for classes or families of similar or related systems.
 
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System design is intended to be the link between the system architecture (at whatever point this milestone is defined in the specific application of the systems engineering process) and the implementation of technological system elements that compose the physical architecture of the system.
 
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These related processes are presented together in the present version of the SEBoK, though effort has been made to distinguish between the corresponding activities.
 
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==General System Architecture and Design Principles and Concepts==
 
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===otion of Interface===
 
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The notion of [[Interface (glossary)|interface]] is one of the most important to consider when defining the architecture of a system. The fundamental aspect of an interface is functional and is defined as inputs and outputs of functions. As functions are performed by physical elements (system elements), inputs/outputs of functions are also carried by physical elements; these are called physical interfaces. Consequentially, both functional and physical aspects are considered in the notion of interface.  A detailed analysis of an interface shows the function ''“send”'' located in one system element, the function ''“receive”'' located in the other one, and the function ''“carry"'' as being performed by the physical interface that supports the input/output flow (see Figure 5).
 
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[[File:SEBoKv075_KA-SystDef_Complete_Interface_Representation.png|400px|thumb|center|'''Figure 4. Complete Interface Representation (Faisandier 2012).''' Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.]]  
 
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In the context of complex exchanges between system elements, particularly in software-intensive systems, a protocol is seen as a physical interface that carries exchanges of data.
 
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===Reuse of System Elements===
 
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Systems engineers frequently utilize existing system elements. This reuse constraint has to be identified as a system requirement and carefully taken into account during architecture and design. One can distinguish three general cases involving system element reuse, as shown in Table 1.
 
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<center>
 
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{|
 
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|+'''Table 1. System Element Re-use Cases (Faisandier 2012).''' Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.
 
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!Re-use Case
 
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!Actions and Comments
 
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|-
 
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|'''Case 1:''' The requirements of the system element are up-to-date and it will be re-used with no modification required.
 
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|
 
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* The system architecture to be designed will have to adapt to the boundaries, interfaces, functions, effectiveness, and behavior of the re-used system element.
 
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* If the system element is not adapted, it is probable that costs, complexity, and risks will increase.
 
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|-
 
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|'''Case 2:''' The requirements of the system element are up-to-date and it will be re-used with possible modifications.
 
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* The system architecture to be designed is flexible enough to accommodate the boundaries, interfaces, functions, effectiveness, and behavior of the re-used system element.
 
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* The design of the reused system element, including its test reports and other documentation, will be evaluated and potentially redesigned.
 
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|-
 
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|'''Case 3:''' The requirements are not up-to-date or do not exist.
 
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* It is necessary to reverse engineer the system element to identify its boundaries, interfaces, functions, performances, and behavior.
 
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* This is a difficult activity, since the extant documentation for the re-used system element is likely unavailable or insufficient.
 
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* Reverse engineering is expensive in terms of both time and money, and brings with it increased risk.
 
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|}
 
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</center>
 
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There is a common idea that reuse is ''free''; however, if not approached correctly, reuse may introduce risks that can be significant for the project (costs, deadlines, complexity).
 
  
 
==References==  
 
==References==  
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===Works Cited===
 
===Works Cited===
  
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ANSI/IEEE. 2000. ''Recommended Practice for Architectural Description for Software-Intensive Systems''. New York, NY, USA: American National Standards Institute (ANSI)/Institute of Electrical and Electronics Engineers (IEEE), ANSI/IEEE 1471-2000.
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ANSI/EIA. 1998. ''Processes for Engineering a System''. Philadelphia, PA, USA: American National Standards Institute (ANSI)/Electronic Industries Association (EIA), ANSI/EIA-632-1998.
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ANSI/EIA. 1998. ''Processes for Engineering a System''. Philadelphia, PA, USA: American National Standards Institute (ANSI)/Electronic Industries Association (EIA), ANSI/EIA-632-1998.  
 
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DOD. 2010. ''DOD Architecture Framework.'' Version 2.02. Arlington, VA, USA: US Department of Defense.  Available at: http://cio-nii.defense.gov/sites/dodaf20/
 
  
 
Faisandier, A. 2012. ''Systems Architecture and Design.'' Belberaud, France: Sinergy'Com.
 
Faisandier, A. 2012. ''Systems Architecture and Design.'' Belberaud, France: Sinergy'Com.
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INCOSE. 2012. ''INCOSE Systems Engineering Handbook,'' Version 3.2.2. San Diego, CA, USA: International Council on Systems Engineering (INCOSE), INCOSE-TP-2003-002-03.2.2.
 
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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. ISO/IEC/IEEE 15288:2015.
 
  
 
ISO/IEC/IEEE. 2011. ''Systems and software engineering - Requirements Engineering''. Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission/ Institute of Electrical and Electronics Engineers (IEEE), (IEC), ISO/IEC/IEEE 29148.
 
ISO/IEC/IEEE. 2011. ''Systems and software engineering - Requirements Engineering''. Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission/ Institute of Electrical and Electronics Engineers (IEEE), (IEC), ISO/IEC/IEEE 29148.
  
 
ISO/IEC/IEEE. 2011. ''Systems and software engineering - Architecture description.'' Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC)/Institute of Electrical and Electronics Engineers (IEEE), ISO/IEC/IEEE 42010.
 
ISO/IEC/IEEE. 2011. ''Systems and software engineering - Architecture description.'' Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC)/Institute of Electrical and Electronics Engineers (IEEE), ISO/IEC/IEEE 42010.
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Maier, M., and E. Rechtin. 2009. ''The Art of Systems Architecting.'' 3rd ed. Boca Raton, FL, USA: CRC Press.
 
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MOD. 2010. ''MOD Architecture Framework.''  Version 1.2.004. UK Ministry of Defence.  Available at: http://www.mod.uk/DefenceInternet/AboutDefence/WhatWeDo/InformationManagement/MODAF/.
 
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Stevens, R., P. Brook, K. Jackson, and S. Arnold. 1998. ''Systems Engineering - Coping with Complexity''. Englewood Cliffs, NJ, USA: Prentice-Hall.
 
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Wilkinson, M., A. James, M. Emes, P. King, P. Bryant. 2010. “Belief Systems in Systems Architecting: Method and Preliminary Applications." Presented at the IEEE SMC Society’s 5th International Conference on System of Systems Engineering (SoSE). 22nd-24th June 2010.  Loughborough University, UK.
 
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Wilkinson, M.K. 2010. “Z8: Systems Architecture”, in Z-guide series. INCOSE UK, available from INCOSE UK at: http://www.incoseonline.org.uk/Program_Files/Publications/zGuides.aspx?CatID=Publications.
 
  
 
===Primary References===
 
===Primary References===
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Blanchard, B.S., and W.J. Fabrycky. 2005. ''[[Systems Engineering and Analysis]].'' 4th ed. Prentice-Hall International Series in Industrial and Systems Engineering. Englewood Cliffs, NJ, USA: Prentice-Hall.  
 
Blanchard, B.S., and W.J. Fabrycky. 2005. ''[[Systems Engineering and Analysis]].'' 4th ed. Prentice-Hall International Series in Industrial and Systems Engineering. Englewood Cliffs, NJ, USA: Prentice-Hall.  
  
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INCOSE. 2012. ''[[INCOSE Systems Engineering Handbook]]: A Guide for System Life Cycle Processes and Activities''.  Version 3.2.2. San Diego, CA, USA: International Council on Systems Engineering (INCOSE), INCOSE-TP-2003-002-03.2.2.
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INCOSE. 2015. '[[INCOSE Systems Engineering Handbook|Systems Engineering Handbook]]: A Guide for System Life Cycle Processes and Activities', version 4.0. Hoboken, NJ, USA: John Wiley and Sons, Inc, ISBN: 978-1-118-99940-0
  
 
ISO/IEC. 2007. ''[[ISO/IEC 26702|Systems Engineering – Application and Management of The Systems Engineering Process]]''. Geneva, Switzerland: International Organization for Standards (ISO)/International Electrotechnical Commission (IEC), [[ISO/IEC 26702]]:2007.
 
ISO/IEC. 2007. ''[[ISO/IEC 26702|Systems Engineering – Application and Management of The Systems Engineering Process]]''. Geneva, Switzerland: International Organization for Standards (ISO)/International Electrotechnical Commission (IEC), [[ISO/IEC 26702]]:2007.
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Buede, D.M. 2009. ''The Engineering Design of Systems: Models and Methods''. 2nd ed. Hoboken, NJ, USA: John Wiley & Sons Inc.  
 
Buede, D.M. 2009. ''The Engineering Design of Systems: Models and Methods''. 2nd ed. Hoboken, NJ, USA: John Wiley & Sons Inc.  
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DoD. 2010. ''DOD Architecture Framework.'' Version 2.02.  Arlington, VA, USA: US Department of Defense. Available at: http://cio-nii.defense.gov/sites/dodaf20/
 
  
 
Faisandier, A. 2012. ''Systems Architecture and Design''. Belberaud, France: Sinergy'Com.
 
Faisandier, A. 2012. ''Systems Architecture and Design''. Belberaud, France: Sinergy'Com.
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MOD. 2010. ''MOD Architecture Framework,'' Version 1.2.004. UK Ministry of Defence. Available at: http://www.mod.uk/DefenceInternet/AboutDefence/WhatWeDo/InformationManagement/MODAF/.
 
MOD. 2010. ''MOD Architecture Framework,'' Version 1.2.004. UK Ministry of Defence. Available at: http://www.mod.uk/DefenceInternet/AboutDefence/WhatWeDo/InformationManagement/MODAF/.
  
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Stevens, R., P. Brook, K. Jackson, S. Arnold. 1998. ''Systems Engineering - Coping with Complexity''. Englewood Cliffs, NJ, USA: Prentice-Hall.
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Wilkinson, M., A. James, M. Emes, P. King, P. Bryant. 2010. ''Belief Systems in Systems Architecting: Method and Preliminary Applications''. paper presented at the IEEE SMC Society’s 5th International Conference on System of Systems Engineering (SoSE). 22nd-24th June 2010.  Loughborough University, UK.
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[[Category:Part 3]][[Category:Knowledge Area]][[Category:System Definition]]
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Revision as of 09:07, 28 October 2019

Lead Authors: Alan Faisandier, Garry Roedler, Contributing Author: Rick Adcock

System definitionSystem definition activities are conducted to create and describe in detail a system-of-interestsystem-of-interest (SoI) to satisfy an identified need. The activities are grouped and described as generic processes. which consist of system requirements definition, system architecture definition, system design definition and system analysis. The architecture definition of the system may include the development of related logical architecture models and physical architecture models. During and/or at the end of any iteration, gap analysis is performed to ensure that all system requirements have been mapped to the architecture and design.

System definition activities build on the artifacts and decisions from concept definitionconcept definition, primarily the articulation of the missionmission of the (SoI), the needs and requirements of stakeholdersneeds and requirements of stakeholders, and preliminary operational concepts. See Life Cycle Processes and Enterprise Need for further detail on the transformation of needs and requirements from the business or enterprise and stakeholder levels of abstraction addressed in concept definition to the system and system element level of abstraction addressed in system definition.

The products of system definition activities (system requirements, architecture and design) are inputs to system realizationsystem realization.

The specific activities and sequence of system definition activities and their involvement with the life cycle activities of any system, and in particular the close integration with concept definition and system realization activities, will be dependent upon the type of life cycle modellife cycle model being utilized. See Applying Life Cycle Processes for further discussion of the concurrent, iterative and recursive nature of these relationships.

Topics

Each part of the SEBoK is divided into knowledge areas (KAs), which are groupings of information with a related theme. The KAs in turn are divided into topics. This KA contains the following topics:

See the article Matrix of Implementation Examples for a mapping of case studies and vignettes included in Part 7 to topics covered in Part 3.

System Views and System Elements

An engineered systemengineered system solution to a defined concept includes a set of engineering elements, characteristics, and properties. These elements are grouped in two ways:

  • Needs and requirements views
  • Architecture and design views

Architecture views include the identification of the boundary and interfaces of a system-of-interest (SoI)system-of-interest (SoI), which may then be further refined as a collection of system elementssystem elements and their relationships.

Needs and Requirements Views

Requirements provide an overall view of the purposepurpose and missionmission which the system as a whole is intended to satisfy, as well as a technology-independent view of that the system solutions(s) should do. They are conventionally organized into two types:

  • System requirementsSystem requirements, which describe the functions which the system as a whole should fulfill in order to satisfy the stakeholder requirements and are expressed in an appropriate set of views, and non-functional requirements expressing the levels of safety, security, reliability, etc., which are called for. These collectively form the basis for verificationverification later in the life cycle.

System requirements and stakeholder requirements are closely related. Neither can be considered complete until consistency between the two has been achieved, as demonstrated by traceability, for which a number of iterations may be needed.

The process activities that are used to identify, engineer and manage system requirements are described further in the System Requirements article in the KA.

Architecture and Design Views

A given engineered system is one solution that could address/answer a problem or an opportunity (represented through requirements views); the solution may be more or less complexcomplex. A complex solution cannot be comprehended with a single view or model, because of the characteristics or properties of the problem/solution (see system complexity). The characteristics are structured as types or entities; types are related to each other. An instantiation of the set of types can be understood as THE architecture of the system. The majority of interpretations of system architecture are based on the fairly intangible notion of structure. Therefore, the system architecture and design is formally represented with sets of types or entities such as functions, interfaces, resource flow items, information elements, physical elements, nodes, links, etc. These entities may possess attributes/characteristics such as dimensions, environmental resilience, availability, reliability, learnability, execution efficiency, etc. The entities are interrelated by the means of relationships and are generally grouped into sets to represent views/models of the system architecture and design.

ViewpointsViewpoints and viewsviews are sometimes specified in architecture frameworksarchitecture frameworks. Views are usually generated from models. Many systems engineering practices use logical and physical views for modeling the system architecture and design.

  • The logical view of the architecturelogical view of the architecture supports the logical operation of the system all along its life cycle, and may include functional, behavioral, and temporal views/models. Operational scenarios refine the mission into a collection of functionsfunctions and dynamic structures that describe how the mission is performed (behavior).
  • The physical view of the architecturephysical view of the architecture is a set of system elementssystem elements performing the functions of the system. Those system elements can be either material or immaterial (e.g., equipment made of hardware, software and/or human roles).

The boundary of the system architecture depends on what engineers include within the scope of the SoI and outside of it. This decision marks the transition from the characterization of the problem context to the beginnings of solution definition.

Facing the potential number of system elements that constitute the physical architecture, sets of system elements can be grouped to form systems. The decomposition of the SoI (highest level) may include the decomposition of several layers of systems (intermediate levels of systems) until technological system elements (lowest level) are defined. Any layer of the decomposition may include systems and non-decomposable technological system elements. The relationship between each layer is recursiverecursive; as a system element is also an engineered system it can be characterized in its turn using the previous views in its own context.

The logical and physical representations of the system architecture are mapped onto each other. The interactions between system elements are defined by interfaces whose complexity strongly depends on the way the system architecture and design is defined. The relationships between the outputs of concept definition and the system solution, as well as the range of other views of a system that are available to describe a more complete set of characteristics between the system elements are discussed further in the Logical Architecture Model Development and Physical Architecture Model Development sections of system definition.

System Synthesis and Decomposition

System definition is managed through methodical synthesissynthesis of the SoI into systems and system elements. Solution synthesis may be top down or bottom up, as discussed in Synthesizing Possible Solutions. However it is done, as the system architecture definition advances, a decomposition of systems and system elements emerges, this forms a system breakdown structure (SBS). For project management purposes, every system of the SBS may be included in a building block, a notion introduced in (ANSI/EIA 1998), also called system blocks.

Stakeholder requirementsStakeholder requirements and system requirementssystem requirements exist at all layers of the SBS. In ISO/IEC/IEEE 29148 Systems and software engineering - Requirements Engineering (ISO 2011), these layers are known as levels of abstraction. Along with systematically introducing layers of systems, the architecture and design process manages the transformation of the system requirements through levels of abstraction. Figure 1 illustrates this approach.

Figure 1. Top-down Development of Architecture and Design, and Requirements (Faisandier 2012). Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.

As shown in Figure 1

  • The white ovals represent requirements at decreasing levels of abstraction, and the arrows represent the transformation of those requirements through the levels using the architecture and design process. Stakeholder expressions of needs, expectations, and constraints are transformed into stakeholder requirements.
  • The next transformation crosses the boundary between the problem and solution areas by converting stakeholder requirements into system requirements, reflecting the bounded solution space.
  • At the SoI level, the system architecture is developed which serves to identify systems and system elements and establishes how they operate together to address the SoI requirements.

This approach is applied recursively for each level of abstraction/decomposition recognizing that the same generic processes are applied at multiple levels of abstraction. At any level of this decomposition one or more solution options may be presented as system architectures. The process by which the solution which best fits the system requirements, associated stakeholder needs and wider life cycle concerns is selected and justified is discussed in the System Analysis process.

Figure 2 below portrays the engineering that occurs in each system block. As necessary, system elements are defined through sets of system element requirements, which become inputs to other system blocks (level n+1). The approach is then recursively applied using the system definition processes.

Figure 2. Recursive Instantiation of Definition Processes (Faisandier 2012). Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.

At the n+1 level, the systems or system elements may also collect other stakeholder requirements that are directly pertinent to this level of architecture and design. Processes within each system are generic, but unique in local purpose, scope and context.

See Applying Life Cycle Processes for a discussion of the iterative and recursive application of system requirements and architecture processes, and Life Cycle Processes and Enterprise Need for further detail on the transformation of needs and requirements to system and system element levels of abstraction.

The different aspects of how systems thinkingsystems thinking is applicable to system definition are discussed in SEBoK Part 2. In particular, see discussion of the recursive nature of systems and engineered system contexts in Engineered System Context; the contrast between top-down and bottom up approaches in Synthesizing Possible Solutions and the role of solution architecture options and selection in Analysis and Selection between Alternative Solutions.

References

Works Cited

ANSI/EIA. 1998. Processes for Engineering a System. Philadelphia, PA, USA: American National Standards Institute (ANSI)/Electronic Industries Association (EIA), ANSI/EIA-632-1998.

Faisandier, A. 2012. Systems Architecture and Design. Belberaud, France: Sinergy'Com.

ISO/IEC/IEEE. 2011. Systems and software engineering - Requirements Engineering. Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission/ Institute of Electrical and Electronics Engineers (IEEE), (IEC), ISO/IEC/IEEE 29148.

ISO/IEC/IEEE. 2011. Systems and software engineering - Architecture description. Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC)/Institute of Electrical and Electronics Engineers (IEEE), ISO/IEC/IEEE 42010.

Primary References

ANSI/EIA. 1998. Processes for Engineering a System. Philadelphia, PA, USA: American National Standards Institute (ANSI)/Electronic Industries Association (EIA), ANSI/EIA 632-1998.

Blanchard, B.S., and W.J. Fabrycky. 2005. Systems Engineering and Analysis. 4th ed. Prentice-Hall International Series in Industrial and Systems Engineering. Englewood Cliffs, NJ, USA: Prentice-Hall.

INCOSE. 2015. 'Systems Engineering Handbook: A Guide for System Life Cycle Processes and Activities', version 4.0. Hoboken, NJ, USA: John Wiley and Sons, Inc, ISBN: 978-1-118-99940-0

ISO/IEC. 2007. Systems Engineering – Application and Management of The Systems Engineering Process. Geneva, Switzerland: International Organization for Standards (ISO)/International Electrotechnical Commission (IEC), ISO/IEC 26702:2007.

ISO/IEC/IEEE. 2015. Systems and Software Engineering - System Life Cycle Processes. Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC) / Institute of Electrical and Electronics Engineers. ISO/IEC/IEEE 15288:2015.

ISO/IEC/IEEE. 2011. Systems and Software Engineering - Requirements Engineering. Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission/ Institute of Electrical and Electronics Engineers (IEEE), (IEC), ISO/IEC/IEEE 29148.

ISO/IEC/IEEE. 2011. Systems and Software Engineering - Architecture Description. Geneva, Switzerland: International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC)/Institute of Electrical and Electronics Engineers (IEEE), ISO/IEC/IEEE 42010.

Martin, J.N. 1997. Systems Engineering Guidebook: A process for developing systems and products, 1st ed. Boca Raton, FL, USA: CRC Press.

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

Additional References

Baldwin, C.Y. and K.B. Clark. 2000. Design Rules. Cambridge, Mass: MIT Press.

Buede, D.M. 2009. The Engineering Design of Systems: Models and Methods. 2nd ed. Hoboken, NJ, USA: John Wiley & Sons Inc.

Faisandier, A. 2012. Systems Architecture and Design. Belberaud, France: Sinergy'Com.

Hatley, D.J., and I.A. Pirbhai. 1987. Strategies for Real-Time System Specification. New York, NY: Dorset House Pub.

MOD. 2010. MOD Architecture Framework, Version 1.2.004. UK Ministry of Defence. Available at: http://www.mod.uk/DefenceInternet/AboutDefence/WhatWeDo/InformationManagement/MODAF/.

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