Difference between revisions of "Physical Architecture Model Development"

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'''''Lead Authors:''''' ''Alan Faisandier, Rick Adcock''
 
'''''Lead Authors:''''' ''Alan Faisandier, Rick Adcock''
 
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Physical Architecture Model Development may be used as a task of the activity "Develop candidate architectures models and views," or a sub-process of the System Architecture Definition process (see '''[[System Architecture]]''' article). Its purpose is to elaborate models and views of a physical, concrete solution that accommodates the {{Term|Logical Architecture (glossary)|logical architecture}} model and satisfies and trades-off system requirements. Once a logical architecture model is defined (see [[Logical Architecture Model Development]]), concrete physical elements have to be identified that can support functional, behavioral, and temporal features as well as the expected properties of the system deduced from non-functional system requirements (e.g. constraint of replacement of obsolescence, and/or continued product support).
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The purpose of the System Design is to supplement the system architecture by providing information and data useful and necessary for implementation of the system elements. Design definition is the process of developing, expressing, documenting, and communicating the realization of the architecture of the system through a complete set of design characteristics described in a form suitable for implementation.
  
A {{Term|Physical Architecture (glossary)|physical architecture}} model is an arrangement of physical elements, ({{Term|System Element (glossary)|system elements}} and {{Term|Physical Interface (glossary)|physical interfaces}}) that provides the solution for a {{Term|Product (glossary)|product}}, {{Term|Service (glossary)|service}}, or {{Term|Enterprise (glossary)|enterprise}}. It is intended to satisfy logical architecture elements and system requirements ISO/IEC/IEEE 26702 (ISO 2007). It is implementable through technological system elements. {{Term|System Requirement (glossary)|System requirements}} are allocated to both the logical and physical architectures. The resulting system architecture is assessed with {{Term|System Analysis (glossary)|system analysis}} and when completed becomes the basis for {{Term|System Realization (glossary)|system realization}}.
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== Concepts and Principles ==
  
In some cases, particularly when multiple systems are to be defined to a common physical architecture model, one of the drivers for the physical architecture model may be interface standards; these physical interfaces may well be one of the most important concerns for these systems.  It is quite possible that such interface standards are mandated at a high level in the system requirements. On the other hand, it is equally possible for standards to be derived during physical architecture model development and these can be critical enablers for desirable engineering outcomes, such as: families of systems, technology insertion, interoperability and “open systems”. For example, today’s video, hi-fi, and computer systems have all benefited from adoption of interface standards.  Other examples exist in most fields of engineering from nuts and bolts, plumbing, electrical installations, rail gauges, TCP/IP, IT systems and software to modular defense and space systems.
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=== Design Notion ===
 +
In industrial practices, the term ''design'' is often used to mean both {{Term|Architecture (glossary)}} and {{Term|Design (glossary)}}. 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 {{Term|complexity (glossary)}} (interconnections level, multi-techno, emergence, etc.).
  
Note: The term ''Physical Architecture'' is a contraction of the expression ''Physical View of the System Architecture''.
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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 described in [[System Architecture]]. Practitioners found the term ''structure'' inadequate to describe all 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.
  
==Concepts and Principles==
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The trend today is to consider system architecture and system design as different and separate sets of activities, but concurrent and strongly intertwined.
  
===System Element, Physical Interface, and Physical Architecture Model===
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System design includes activities to conceive a set of system elements that answers a specific, intended purpose, using principles and concepts; it includes assessments and decisions to select system 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.
A system element is a discrete part of a system that can be implemented to fulfill design properties. A system element can be hardware, software, data, humans, processes (e.g., processes that provide a service to users), procedures (e.g., operator instructions), facilities, materials, and naturally occurring entities (e.g., water, organisms, and minerals), or any combination of these ISO/IEC/IEEE 15288 (ISO 2015). A {{Term|Physical Interface (glossary)|physical interface}} binds two system elements together; this is similar to a link or a connector. Table 1 provides some examples of system elements and physical interfaces.
 
  
{|
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=== Design Characteristics and Design Enablers ===
|+'''Table 1. Types of System Elements and Physical Interfaces.''' (SEBoK Original)
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Every technological domain or discipline owns its peculiar laws, rules, theories, and enablers concerning transformational, structural, behavioral, and temporal properties of its composing parts of materials, energy, or information. These specific parts and/or their compositions are described with typical design characteristics and enablers. These allow achieving the implementation of every system element through various transformations and exchanges required by design characteristics (e.g., operability level, reliability rate, speed, safeguard level) that have been assigned during the system architecture definition process.
!Element
 
!Product System
 
!Service System
 
!Enterprise System
 
|-
 
|'''System Element'''
 
|
 
* Hardware Parts (mechanics, electronics, electrical, plastic, chemical, etc.)
 
* Operator Roles
 
* Software Pieces
 
|
 
* Processes, Data Bases, Procedures, etc.
 
* Operator Roles
 
* Software Applications
 
|
 
* Corporate, Direction, Division, Department, Project, Technical Team, Leader, etc.
 
* IT Components
 
|-
 
|'''Physical Interface'''
 
|* Hardware Parts, Protocols, Procedures, etc.
 
|* Protocols, Documents, etc.
 
|* Protocols, Procedures, Documents, etc.
 
|}
 
 
 
A complex system composed of thousands of physical and/or intangible parts may be structured in several layers of {{Term|System (glossary)|systems}} and {{Term|System Element (glossary)|system elements}}. The number of elements in a level of the structure of one system is limited to only a few, in order to facilitate managing the system definition; a common guideline is ''five plus or minus two'' elements (see illustration in Figure 1).
 
 
 
[[File:SEBoKv075_KA-SystDef_Limited_nb_in_decomposition.png|500px|thumb|center|'''Figure 1. Layers of Systems and System Elements (Faisandier 2012).''' Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.]]
 
 
 
A physical architecture model is built from systems, system elements, and all necessary physical interfaces between these elements, as well as from external elements (neighboring or enabling systems and/or system elements in the considered layer and concerned elements in the context of the global system-of-interest) - see illustration in Figure 2.
 
 
 
[[File:SEBoKv075_KA-SystDef_Encapsulation.png|600px|thumb|center|'''Figure 2. Physical Architecture Model Representation (Faisandier 2012).''' Permission granted by Sinergy'Com. All other rights are reserved by the copyright owner.]]
 
 
 
===Design Property===
 
A {{Term|Design Property (glossary)|design property}} is a property that is obtained during system architecture and created through the assignment of non-functional requirements, estimates, analyses, calculations, simulations of a specific aspect, or through the definition of an existing element associated with a system element, a physical interface, and/or a physical architecture. If the defined element complies with a requirement, the design property will relate to (or may equal) the requirement. Otherwise, one has to identify any discrepancy that could modify the requirement or design property and detect any deviations.
 
 
 
Stakeholders have concerns that correspond to the expected behavior of a system within operational, environmental, and/or physical constraints as well as to more general life cycle constraints. {{Term|Stakeholder Requirement (glossary)|Stakeholder requirements}} and {{Term|System Requirement (glossary)|system requirements}} express these concerns as expected capabilities from the system (e.g., usability, interoperability, security, expandability, environment suitability, etc.). Architects and/or designers identify these capabilities from requirements and deduce corresponding quantitative or qualitative design properties to properly equip their physical architecture model (e.g., reliability, availability, maintainability, modularity, robustness, operability, climatic environment resistance, dimensions limits, etc.).  For further discussion on how some of these properties may be included in architecture and design, please see the article [[Systems Engineering and Specialty Engineering]] in the [[Related Disciplines]] knowledge area (KA).
 
  
===Allocation of Logical Elements to Physical Elements and Partitioning===
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The design definition provides the description of the design characteristics and design enablers necessary for implementation. Design characteristics include dimensions, shapes, materials, and data processing structures. Design enablers include formal expressions or equations, drawings, diagrams, tables of metrics with their values and margins, patterns, algorithms, and heuristics.
Developing a candidate physical architecture model for a system consists of first identifying the system elements that can perform functions of the logical architecture model as well as identifying the interfaces capable of carrying out the input-output flows and control flows. When identifying potential elements, a systems engineer needs to allocate design properties within the logical architecture; these properties are deduced from the [[System Requirements|system requirements]]. Partitioning and allocation are activities to decompose, gather, or separate functions in order to facilitate the identification of feasible system elements that support these functions. Either they exist and can be reused or re-purposed, or they can be developed and technically implemented.
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* Examples of generic design characteristics in mechanics of solids: shape, geometrical pattern, dimension, volume, surface, curves, resistance to forces, distribution of forces, weight, velocity of motion, temporal persistence
 +
* Examples of generic design characteristics in software: distribution of processing, data structures, data persistence, procedural abstraction, data abstraction, control abstraction, encapsulation, creational patterns (e.g., builder, factory, prototype, singleton), and structural patterns (e.g., adapter, bridge, composite, decorator, proxy)
  
Partitioning and allocation use criteria to find potential affinities between functions. Systems engineers use system requirements and/or design properties as criteria to assess and select candidate system elements and partitions of functions, such as similar transformations within the same technology, similar levels of efficiency, exchange of the same type of input-output flows (information, energy, and materials), centralized or distributed controls, execution with close frequency level, dependability conditions, environment resistance level, and other enterprise constraints.
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=== Relation with System Architecture ===
 +
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 model of the system.
  
A concurrent engineering approach is necessary when several different sets of technologies, knowledge, and skills are necessary to establish a candidate physical architecture model. This is particularly true during the partition and allocation of functions to various system elements, in which the systems engineer must account for compatibility issues and {{Term|Emergent Property (glossary)|emergent properties}}. (See SEBoK Part 2: [[Synthesizing Possible Solutions]] for a discussion of possible approaches.)
+
Design definition is driven by specified requirements, the system architecture, and more detailed analysis of performance and feasibility. It addresses the implementation technologies and their assimilation. Design provides the “how-” or “implement-to” level of the definition.
  
===Developing Candidate Physical Architecture Models===
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Design concerns every system element composed of implementation technologies, such as mechanics, electronics, software, chemistry, human operations and services for which specific engineering processes are needed. System design provides feedback to the parent system architecture to consolidate or confirm the allocation and partitioning of architectural characteristics and design properties to system elements.
The goal of physical architecture model development activities is to provide the best possible physical architecture model made of suitable systems, technological system elements, and physical interfaces (i.e., the architecture that answers, at best, all system requirements, depending on agreed limits or margins of each requirement). The best way to do this is to produce several candidate physical architecture models, assess and compare them, and then select the most suitable one.
 
  
A candidate physical architecture model is elaborated according to affinity criteria in order to build a set of system elements (i.e., separate, gather, connect, and disconnect the network of system elements and their physical interfaces). These criteria are the same as those used for partitioning and allocating functions to system elements. The physical architecture model development may be focused in different ways, for example, it may address:
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=== Design Descriptor ===
 +
A design descriptor is the set of generic design characteristics and of their possible values. If similar, but not exact system elements exist, it is possible to analyze these in order to identify their basic characteristics. Variations of the possible values of each characteristic determine potential candidate system elements.
  
*  Reduction in the number of physical interfaces
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=== Holistic Design ===
*  System elements that can be tested separately
+
Holistic design is an approach that considers the system being designed as an interconnected whole, which is also part of something larger. Holistic concepts can be applied to the system as a whole along with the system in its context (e.g., the enterprise or mission in which the system participates), as well as the design of mechanical devices, the layout of spaces, and so forth. This approach often incorporates concerns about the environment, considering how the design will impact the environment and attempting to reduce environmental impact. Holistic design is about more than merely trying to meet the system requirements.
*  Compatible technology
 
*  Measures of the proximity of elements in space
 
*  Ease of handling (weight, volume, and transportation facilities)
 
*  Optimization of resources shared between elements
 
*  Modularity (i.e. elements have low interdependence)
 
*  Resilience (i.e. elements which are highly reliable, maintainable or replaceable)
 
  
===Evaluating and Selecting the Preferred Candidate===
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== Process Approach ==
Viable physical architecture models enable all required functions or capabilities specified in the logical architecture model to be realized. Architecture and design activity includes evaluation to obtain a balance among design properties, costs, risks, etc. Generally, the physical architecture model of a system is determined more strongly by non-functional requirements (e.g., performance, safety, security, environmental conditions, constraints, etc.) than by functions. There may be many (physical) ways to establish functions but fewer ways of satisfying non-functional requirements. The preferred physical architecture model represents the selection of system elements, their physical relationships, and interfaces. Typically, this physical architecture will still leave further systems engineering to be undertaken to achieve a fully optimized system after any remaining trade-offs are made and algorithms and parameters of the system are finalized.
 
Certain analyses (efficiency, dependability, cost, risks, etc.) are required to get sufficient data that characterize the global behavior and structure of the candidate architectures in regard to system requirements; this is often broadly referred to as [[System Analysis|system analysis]]. Other analyses and assessments require knowledge and skills from the different involved technologies and specialties (mechanics, electronics, software, thermodynamics, electro-magnetic compatibility, safety, security etc.). They are performed through corresponding specialist analysis of the system.
 
  
===Legacy Systems and Systems of Systems===
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=== Purpose ===
Few systems come into existence or operate without interacting with others in a {{Term|System Context (glossary)|system context}}. These interactions may be with other operational systems, or maintenance and support systems, which in turn may be legacy (already in use) or future legacy (under development and likely to operate with the system of interest in the future).  
+
The purpose of the System Design process is to provide sufficient detailed data and information about the system and its system elements to enable the implementation consistent with architectural entities as defined in models and views of the system architecture (ISO/IEC/IEEE 15288 [ISO 2015]).  
  
The best chosen approach will be dependent on the strength of interactions between the {{Term|System-of-Interest (glossary)}} (SoI) and its wider context. While these interactions are small, they may be accounted for by defining a set of static external interface requirements (for example, technical standards) with which the system must comply, by including these as constraints in the system requirements and ensuring compliance through design assurance.
+
Generic inputs include architecture description of the parent system and system element requirements.
  
Where the interactions are more intense (for example, where continuous information is to be exchanged with other systems), these will have to be recognized as part of a {{Term|System of Systems (SoS) (glossary)|system of systems}} context and will instead be considered as part of an {{Term|Enterprise Systems Engineering (ESE) (glossary)|enterprise systems engineering}} approach.  
+
Generic outputs are the description of the design characteristics and design enablers necessary for implementation.
  
Another important consideration may be the sharing of technology or system elements between the SoI and other systems, often as part of a family of systems (many examples occur in automotive and aerospace industries) or the re-use of system elements from existing legacy. Here a degree of top-down or middle-out design work will be necessary to ensure the system of interest embodies the required system elements, while conforming as far as possible to the stakeholder and system requirements, with any compromises being understood and managed.
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=== Activities of the Process ===
 
 
If a System-of-Interest is intended to be used in one or more {{Term|Service System (glossary)|service systems}} or {{Term|System of Systems (SoS) (glossary)|system of systems}} configurations, this will affect its physical architecture model.  One of the features of these SoS is the late binding of component systems in use.  Such component systems must be architected with open or configurable interfaces, must have clearly defined functions packaged in such a way as to be relevant to the SoS using them, and must include some method by which they can be identified and included in the SoS when needed. 
 
 
 
Both service systems and SoS will be defined by a high-level physical architecture model, which will be utilized to define the relevant SoS relationships, interfaces, and constraints that should be included in [[Concept Definition]].  The results will be embedded in the stakeholder and system requirements and handled through interface agreements and across-project communication during development, realization, and use. 
 
 
 
See SEBoK Part 4: [[Applications of Systems Engineering]] for more information on special considerations for architecting SoS.
 
 
 
==Process Approach==
 
===Purpose===
 
The purpose of the Physical Architecture Model Development is to define, select, and synthesize a system physical architecture model which can support the logical architecture model. A physical architecture model will have specific properties to address stakeholder concerns or environmental issues and to satisfy system requirements.
 
 
 
Because of the evolution of the {{Term|System Context (glossary)|context of use}} or technological possibilities, the physical architecture which is composed of {{Term|System Element (glossary)|system elements}} is supposed to evolve along the life cycle of the system in order for it to continue to perform its mission within the limits of its required effectiveness. Depending on whether or not evolution impacts {{Term|Logical Architecture (glossary)|logical architecture}}  model elements, allocations to system elements may change. A physical architecture model is equipped with specific {{Term|Design Property (glossary)|design properties}} to continuously challenge the evolution.
 
 
 
'''Generic inputs''' include the selected logical architecture model, system requirements, generic patterns and properties that architects identify and utilize to answer requirements, outcomes from system analysis, and feedback from system verification and system validation.
 
 
 
'''Generic outputs''' are the selected physical architecture model, allocation matrix of functional elements to physical elements, traceability matrix with system requirements, stakeholder requirements of each system and system element composing the physical architecture model, and rejected solutions.
 
 
 
===Activities of the Process===
 
 
Major activities and tasks to be performed during this process include the following:
 
Major activities and tasks to be performed during this process include the following:
  
* Partition and allocate functional elements to system elements:
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==== 1. Initialize design definition ====
** Search for system elements or technologies able to perform functions and physical interfaces to carry input-output and control flows. Ensure system elements exist or can be engineered. Assess each potential system element using criteria deduced from design properties (themselves deduced from non-functional system requirements).
+
* Plan for technology management for the whole system. Identify the technologies (mechanics, electricity, electronics, software, biology, operators, etc.) that would compose and implement the system elements and their physical interfaces.
** Partition functional elements (functions, scenarios, input-outputs, triggers, etc.) using the given criteria and allocate partitioned sets to system elements (using the same criteria).
+
* Determine which technologies and system elements have a risk to become obsolete or evolve during the operation stage of the system. Plan for their potential replacement.
** When it is impossible to identify a system element that corresponds to a partitioned functional set, decompose the function until the identification of implementable system elements is possible.
+
* Identify types of design characteristics or properties for each technology of each system element.
** Check the compatibility of technologies and the compatibility of interfaces between selected system elements.
+
* Periodically assess design characteristics and adjust as the system evolves.
* Constitute candidate physical architecture models.
+
* Document the design definition strategy, including the need for and requirements of any enabling systems, products, or services to perform the design.
** Because partitioned sets of functions can be numerous, there are generally too many system elements. For defining controllable architectures, system elements have to be grouped into higher-level system elements known as system element groups, often called sub-systems in industry.
 
** Constitute several different system element groups corresponding to different combinations of elementary system elements. One set of system element groups plus one or several non-decomposable system elements forms a candidate physical architecture model of the considered system.
 
** Represent (using patterns) the physical architecture model of each system element group connecting its system elements with physical interfaces that carry input-output flows and triggers. Add physical interfaces as needed; in particular, add interfaces with external elements to the system element group.
 
** Represent the synthesized physical architecture of the considered system built from system element groups, non-decomposable systems, and physical interfaces inherited from the physical architecture model of system element groups.
 
** Enhance the physical architecture model with design properties such as modularity, evolution capability, adaptability to different environments, robustness, scalability, resistance to environmental conditions, etc.
 
** If possible, use executable architecture prototypes (e.g., hardware-software (HW-SW)-in-the-loop prototypes) for identifying potential deficiencies and correct the architecture as needed.
 
* Assess physical architecture model candidates and select the most suitable one:
 
** Use the system analysis process to perform assessments (see the [[System Analysis]] topic).
 
** Use the Decision Management process to support the trades and selection of the preferred alternative (see the [[Decision Management]] topic).
 
* Synthesize the selected physical architecture model:
 
** Formalize physical elements and properties. Verify that system requirements are satisfied and that the solution is realistic.
 
** Identify the derived physical and functional elements created for the necessity of architecture and design and the corresponding system requirements.
 
** Establish traceability between system requirements and physical elements as well as allocate matrices between functional and physical elements.
 
  
===Artifacts, Methods and Modeling Techniques===
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==== 2. Establish design characteristics and design enablers related to each system element ====
Physical architecture descriptions use modeling techniques to create and represent physical architectures. Some common physical models include structural blocks, mass, layout and other models. Modeling techniques may be:
+
* Perform, consolidate or detail system requirements allocation to system elements for all requirements and system elements not fully addressed in the System Architecture process (normally, every system requirement would have been transformed into architectural entities and architectural characteristics within the System Architecture process, which are then allocated to system elements through direct assignment or some partitioning).
 +
* Define the design characteristics relating to the architectural characteristics and check that they are implementable. Use design enablers, such as models (physical and analytical), design heuristics, etc. If the design characteristics are not feasible, then assess other design alternatives or implementation option, or perform trades of other system elements definition.
 +
* Define the interfaces that were not defined by the System Architecture process or that need to be refined as the design details evolve. This includes both internal interfaces between the system elements and the external interfaces with other systems.
 +
* Record the design characteristics of each system element within the applicable artifacts (they depend on the design methods and techniques used).
 +
* Provide rationale about selection of major implementation options and enablers.
  
*  Physical block diagrams (PBD)
+
==== 3. Assess alternatives for obtaining system elements ====
* SysML block definition diagrams (BDD)
+
* Identify existing implemented system elements (COTS/NDI, reused, or other non-developed system elements). Alternatives for new system elements to be developed may be studied.
* Internal block diagrams (IBD) (OMG 2010)
+
* Assess design options for the system element, using selection criteria that are derived from the design characteristics.
* Executable architecture prototyping
+
* Select the most appropriate alternatives.
* Etc.
+
* If the decision is made to develop the system element, the rest of the design definition process and the implementation process are used. If the decision is to buy or reuse a system element, the acquisition process may be used to obtain the system element.
  
Depending on the type of domain for which it is to be used (defense, enterprise, etc.), {{Term|Architecture Framework (glossary)|architecture frameworks}} may provide descriptions that can help to trade-off candidate architectures. Please see section 'Enterprise Architecture Frameworks & Methodologies' in [[Enterprise Systems Engineering Key Concepts]].
+
==== 4. Manage the design ====
 +
* Capture and maintain the rationale for all selections among alternatives and decisions for the design, architecture characteristics, design enablers, and sources of system elements.
 +
* Assess and control the evolution of the design characteristics, including the alignment with the architecture.
 +
* Establish and maintain traceability between design characteristics and architectural characteristics, and with requirements as necessary.
 +
* Provide baseline information for configuration management.
 +
* Maintain the design baseline and the design definition strategy.
  
==Practical Considerations==
+
== Practical Considerations ==
Key pitfalls and good practices related to physical architecture development are described in the next two sections.
+
Key pitfalls and proven practices related to system design are described in the next two sections.
 
 
===Pitfalls===
 
Some of the key pitfalls encountered in performing physical architecture model development are provided in Table 3.
 
  
 +
=== Pitfalls ===
 +
Some of the key pitfalls encountered in performing system design are provided in Table 1.
 
{|
 
{|
|+'''Table 3. Pitfalls with Physical Architecture Development.''' (SEBoK Original)
+
|+
 +
'''Table 1. Pitfalls with System Design.'''(SEBoK Original)
 
!Pitfall
 
!Pitfall
 
!Description
 
!Description
 
|-
 
|-
|Too Many Levels in a Single System Block
+
|'''Consider the design of each system element separately'''
|The current system block includes too many levels of decomposition. The right practice is that the physical architecture model of a system block is composed of one single level of systems and/or system elements.
+
|This would be conducted using heterogeneous implementation of a given technology or between technologies within the system-of-interest. The design strategy for the complete system is defined to find synergies and/or commonalities that could help operation and maintenance of system elements.
|-
 
|No Logical Architecture Model
 
|The developers perform a direct passage from system requirements to a physical architecture model without establishing a logical architecture model; this is a common wrong practice that mainly takes place when dealing with repeating systems and products because the functions are already known. The issue is that a function is always associated with input-output flows defined in a specific domain set. If the domain set changes, the performance of the function can become invalid.
 
|-
 
|Direct Allocation on Technologies
 
|At a high level of abstraction of multidisciplinary systems, directly allocating the functions onto technologies of the lowest level of abstraction, such as hardware or software, does not reflect a system comprehension. The right practice is to consider criteria to decompose the architecture into the appropriate number of levels, alternating logical and physical before reaching the technology level ( the last level of the system).
 
 
|}
 
|}
  
===Proven Practices===+
+
=== Proven Practices ===
 
+
Some proven practices gathered from the references are provided in Table 2.
Some proven practices gathered from the references are provided in Table 4.
 
 
 
 
{|
 
{|
|+'''Table 4. Proven Practices with Physical Architecture Development.''' (SEBoK Original)
+
|+
 +
'''Table 2. Proven Practices with System Design.'''(SEBoK Original)
 
!Practice
 
!Practice
 
!Description
 
!Description
 
|-
 
|-
|Modularity
+
|'''Architecture and design mutual support'''
|Restrict the number of interactions between the system elements and consider the modularity principle (maximum of consistency inside the system element, minimum of physical interfaces with outside) as the right way for architecting systems.
+
|Discipline engineers perform the design definition of each system element; they provide strong support (knowledge and competencies) to systems engineers or architects in the evaluation and selection of candidate system architectures and system elements. Inversely, systems engineers, or architects, must provide feedback to discipline engineers to improve knowledge and know-how.
|-
 
|Focus on Interfaces
 
|Focusing on interfaces rather than on system elements is another key element of a successful architecture and design for abstract levels of systems.
 
 
|}
 
|}
  
==References==
+
== References ==
===Works Cited===
 
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. ''[[ISO/IEC/IEEE 15288|Systems and Software Engineering -- System Life Cycle Processes]]''. Geneva, Switzerland: International Organisation for Standardisation (ISO) /International Electrotechnical Commissions (IEC)/ Institute of Electrical and Electronics Engineers (IEEE). ISO/IEC/IEEE 15288:2015.
+
=== Works Cited ===
 +
INCOSE. 2015. ''INCOSE Systems Engineering Handbook,'' Version 4. San Diego, CA, USA: International Council on Systems Engineering (INCOSE), INCOSE-<u>TP-2003-002-03.2.2</u>.
  
OMG. 2010. ''OMG Systems Modeling Language Specification'', version 1.2, July 2010. Available at: http://www.omg.org/technology/documents/spec_catalog.htm.
+
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 (IEEE). ISO/IEC/IEEE 15288:2015.
  
 
Faisandier, A. 2012. ''Systems Architecture and Design''. Belberaud, France: Sinergy'Com.
 
Faisandier, A. 2012. ''Systems Architecture and Design''. Belberaud, France: Sinergy'Com.
  
===Primary References===
+
=== Primary References ===
ANSI/IEEE. 2000. ''[[IEEE 1471|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.
 
  
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/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 (IEEE). ISO/IEC/IEEE 15288:2015.
 
ISO/IEC/IEEE. 2015. ''[[ISO/IEC/IEEE 15288|Systems and Software Engineering -- System Life Cycle Processes]]''. Geneva, Switzerland: International Organisation for Standardisation (ISO)/International Electrotechnical Commissions (IEC)/Institute of Electrical and Electronics Engineers (IEEE). ISO/IEC/IEEE 15288:2015.
 
ISO/IEC/IEEE. 2011. ''[[ISO/IEC/IEEE 42010|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]].
 
  
===Additional References===
+
Faisandier, A. 2012. ''Systems Architecture and Design''. Belberaud, France: Sinergy'Com.
  
Maier, M., and E. Rechtin. 2009. ''[[The Art of Systems Architecting]],'' 3rd ed. Boca Raton, FL, USA: CRC Press.
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=== Additional References ===
 +
Baldwin, C.Y. and K.B. Clark. 2000. ''Design Rules''. Cambridge, MA, USA: MIT Press.
  
Holland, J.H. 2006. "Studying Complex Adaptive Systems." ''Journal of Systems Science and Complexity.'' vol. 19, no. 1 pp. 1-8. Available at: http://hdl.handle.net/2027.42/41486.
+
Buede, D.M. 2009. ''The Engineering Design of Systems: Models and Methods''. 2nd ed. Hoboken, NJ, USA: John Wiley & Sons Inc.  
  
Thome, B. 1993. ''Systems Engineering, Principles & Practice of Computer-Based Systems Engineering.'' New York, NY, USA: Wiley.
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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/
  
The Open Group. 2011. ''TOGAF'', version 9.1. Hogeweg, The Netherlands: Van Haren Publishing. Accessed August 29, 2012. Available at: https://www2.opengroup.org/ogsys/jsp/publications/PublicationDetails.jsp?catalogno=g116.
 
 
Zachman, J. 2008. "John Zachman's Concise Definition of The Zachman Framework™." Zachman International Enterprise Architecture.  Accessed August 29, 2012.  Available at: http://www.zachman.com/about-the-zachman-framework.
 
 
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Revision as of 18:44, 1 February 2020


Lead Authors: Alan Faisandier, Rick Adcock


The purpose of the System Design is to supplement the system architecture by providing information and data useful and necessary for implementation of the system elements. Design definition is the process of developing, expressing, documenting, and communicating the realization of the architecture of the system through a complete set of design characteristics described in a form suitable for implementation.

Concepts and Principles

Design Notion

In industrial practices, the term design is often used to mean both architecturearchitecture and designdesign. 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 complexitycomplexity (interconnections level, multi-techno, emergence, etc.).

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 described in System Architecture. Practitioners found the term structure inadequate to describe all 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.

The trend today is to consider system architecture and system design as different and separate sets of activities, but concurrent and strongly intertwined.

System design includes activities to conceive a set of system elements that answers a specific, intended purpose, using principles and concepts; it includes assessments and decisions to select system 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.

Design Characteristics and Design Enablers

Every technological domain or discipline owns its peculiar laws, rules, theories, and enablers concerning transformational, structural, behavioral, and temporal properties of its composing parts of materials, energy, or information. These specific parts and/or their compositions are described with typical design characteristics and enablers. These allow achieving the implementation of every system element through various transformations and exchanges required by design characteristics (e.g., operability level, reliability rate, speed, safeguard level) that have been assigned during the system architecture definition process.

The design definition provides the description of the design characteristics and design enablers necessary for implementation. Design characteristics include dimensions, shapes, materials, and data processing structures. Design enablers include formal expressions or equations, drawings, diagrams, tables of metrics with their values and margins, patterns, algorithms, and heuristics.

  • Examples of generic design characteristics in mechanics of solids: shape, geometrical pattern, dimension, volume, surface, curves, resistance to forces, distribution of forces, weight, velocity of motion, temporal persistence
  • Examples of generic design characteristics in software: distribution of processing, data structures, data persistence, procedural abstraction, data abstraction, control abstraction, encapsulation, creational patterns (e.g., builder, factory, prototype, singleton), and structural patterns (e.g., adapter, bridge, composite, decorator, proxy)

Relation with System Architecture

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 model of the system.

Design definition is driven by specified requirements, the system architecture, and more detailed analysis of performance and feasibility. It addresses the implementation technologies and their assimilation. Design provides the “how-” or “implement-to” level of the definition.

Design concerns every system element composed of implementation technologies, such as mechanics, electronics, software, chemistry, human operations and services for which specific engineering processes are needed. System design provides feedback to the parent system architecture to consolidate or confirm the allocation and partitioning of architectural characteristics and design properties to system elements.

Design Descriptor

A design descriptor is the set of generic design characteristics and of their possible values. If similar, but not exact system elements exist, it is possible to analyze these in order to identify their basic characteristics. Variations of the possible values of each characteristic determine potential candidate system elements.

Holistic Design

Holistic design is an approach that considers the system being designed as an interconnected whole, which is also part of something larger. Holistic concepts can be applied to the system as a whole along with the system in its context (e.g., the enterprise or mission in which the system participates), as well as the design of mechanical devices, the layout of spaces, and so forth. This approach often incorporates concerns about the environment, considering how the design will impact the environment and attempting to reduce environmental impact. Holistic design is about more than merely trying to meet the system requirements.

Process Approach

Purpose

The purpose of the System Design process is to provide sufficient detailed data and information about the system and its system elements to enable the implementation consistent with architectural entities as defined in models and views of the system architecture (ISO/IEC/IEEE 15288 [ISO 2015]).

Generic inputs include architecture description of the parent system and system element requirements.

Generic outputs are the description of the design characteristics and design enablers necessary for implementation.

Activities of the Process

Major activities and tasks to be performed during this process include the following:

1. Initialize design definition

  • Plan for technology management for the whole system. Identify the technologies (mechanics, electricity, electronics, software, biology, operators, etc.) that would compose and implement the system elements and their physical interfaces.
  • Determine which technologies and system elements have a risk to become obsolete or evolve during the operation stage of the system. Plan for their potential replacement.
  • Identify types of design characteristics or properties for each technology of each system element.
  • Periodically assess design characteristics and adjust as the system evolves.
  • Document the design definition strategy, including the need for and requirements of any enabling systems, products, or services to perform the design.

2. Establish design characteristics and design enablers related to each system element

  • Perform, consolidate or detail system requirements allocation to system elements for all requirements and system elements not fully addressed in the System Architecture process (normally, every system requirement would have been transformed into architectural entities and architectural characteristics within the System Architecture process, which are then allocated to system elements through direct assignment or some partitioning).
  • Define the design characteristics relating to the architectural characteristics and check that they are implementable. Use design enablers, such as models (physical and analytical), design heuristics, etc. If the design characteristics are not feasible, then assess other design alternatives or implementation option, or perform trades of other system elements definition.
  • Define the interfaces that were not defined by the System Architecture process or that need to be refined as the design details evolve. This includes both internal interfaces between the system elements and the external interfaces with other systems.
  • Record the design characteristics of each system element within the applicable artifacts (they depend on the design methods and techniques used).
  • Provide rationale about selection of major implementation options and enablers.

3. Assess alternatives for obtaining system elements

  • Identify existing implemented system elements (COTS/NDI, reused, or other non-developed system elements). Alternatives for new system elements to be developed may be studied.
  • Assess design options for the system element, using selection criteria that are derived from the design characteristics.
  • Select the most appropriate alternatives.
  • If the decision is made to develop the system element, the rest of the design definition process and the implementation process are used. If the decision is to buy or reuse a system element, the acquisition process may be used to obtain the system element.

4. Manage the design

  • Capture and maintain the rationale for all selections among alternatives and decisions for the design, architecture characteristics, design enablers, and sources of system elements.
  • Assess and control the evolution of the design characteristics, including the alignment with the architecture.
  • Establish and maintain traceability between design characteristics and architectural characteristics, and with requirements as necessary.
  • Provide baseline information for configuration management.
  • Maintain the design baseline and the design definition strategy.

Practical Considerations

Key pitfalls and proven practices related to system design are described in the next two sections.

Pitfalls

Some of the key pitfalls encountered in performing system design are provided in Table 1.

Table 1. Pitfalls with System Design.(SEBoK Original)
Pitfall Description
Consider the design of each system element separately This would be conducted using heterogeneous implementation of a given technology or between technologies within the system-of-interest. The design strategy for the complete system is defined to find synergies and/or commonalities that could help operation and maintenance of system elements.

Proven Practices

Some proven practices gathered from the references are provided in Table 2.

Table 2. Proven Practices with System Design.(SEBoK Original)
Practice Description
Architecture and design mutual support Discipline engineers perform the design definition of each system element; they provide strong support (knowledge and competencies) to systems engineers or architects in the evaluation and selection of candidate system architectures and system elements. Inversely, systems engineers, or architects, must provide feedback to discipline engineers to improve knowledge and know-how.

References

Works Cited

INCOSE. 2015. INCOSE Systems Engineering Handbook, Version 4. San Diego, CA, USA: International Council on Systems Engineering (INCOSE), INCOSE-TP-2003-002-03.2.2.

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 (IEEE). ISO/IEC/IEEE 15288:2015.

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

Primary References

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 (IEEE). ISO/IEC/IEEE 15288:2015.

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

Additional References

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

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

DoD. 2010. DOD Architecture Framework. Version 2.02. Arlington, VA, USA: US Department of Defense. Available at: http://cio-nii.defense.gov/sites/dodaf20/


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