10th System of Systems Engineering Conference, 2015
A key element differentiating traditional systems from systems of systems is governance. While sy... more A key element differentiating traditional systems from systems of systems is governance. While systems are characterized by belonging to a single governing authority, systems within a system of systems are often independently governed or governed by fully empowered entities. Such independence is a necessary condition for the autonomy of each constituent system and for enabling the concept of belonging. At the same time, the capability to be autonomous and the voluntary nature of belonging, enables a constituent system to voluntarily abandon the system of systems it belongs to as well. Yet, research has not addressed so far the implications and modeling of intended abandonment into the operational effectiveness of a system of systems. This paper presents the concept of system abandonment as a philosophical necessity in the definition of systems of systems, it discusses some visions to measure the risk of abandonment, and proposes a way forward to explore mitigation techniques.
Requirement engineering is the cornerstone of systems engineering. Numerous large scale engineere... more Requirement engineering is the cornerstone of systems engineering. Numerous large scale engineered systems face schedule delays, cost overruns and performance shortfalls that can be traced back to the requirements they need to fulfill. In fact, previous research has demonstrated strong relationship between requirements and systems affordability. This paper summarizes and puts into context the authors’ novel contributions in three domains of requirements engineering: systems theory, complexity science, and systems methodologies. The authors propose new theorems and their proofs on requirements affecting affordability, propose a new complexity metric at requirement stage that measures the complexity limit of the system at conceptual stage (even before a specific design is determined), and propose two methodologies to elicit excess-free requirement sets and to identify conflicting requirements more effectively. The paper showcases the value of structuring a research in such a manner, i.e. from theory to practice, enabling strengthening the bounds between theorists and practitioners.
Systems engineering has been successfully applied to a wide variety of industries, which include... more Systems engineering has been successfully applied to a wide variety of industries, which include defense, space, energy, or transportation. All those systems have in common that they are engineered systems and/or socio-technical ones. Yet, systems engineering is considered both an art and a science. Therefore, could systems engineering be or have been applied in the domain of art, even if not done explicitly? Being one of the authors of this paper a systems engineer and the other one a music composer, this paper reports on the reflections of mutual discussions about how each of us of carried out our activities in our respective domain. Interestingly, it turns out that engineering a space system and creating a film original score abstractly follow the same set of principles and practices.
The term solution space is widely used in the engineering community; yet there is little known ab... more The term solution space is widely used in the engineering community; yet there is little known about their evolution. Theoretical research in the field of systems science indicates that requirements can only reduce the solution space. Yet, some authors state that on the contrary requirements can be used to expand to or open new solution spaces. Furthermore, some practitioners defend that the requirement to use a previously nonexistent technology would actually increase the solution space or move it to a new area, while others state that more requirements make life more difficult. Who is right then? The present paper provides initial answers to this question using systems theory. In order to achieve this, the present paper differentiates between various types of solutions spaces, which depend on the systems they include. Finally, the paper provides practical examples to showcase the results of the theoretical findings within real contexts.
Conventional approaches to system design use requirements as boundary conditions against which th... more Conventional approaches to system design use requirements as boundary conditions against which the design activity occurs. Decisions at a given level of the architecture decomposition can result in a flowing down of conflicting requirements, which are easy to fulfill in isolation but extremely difficult when dealt with simultaneously. Designing against such sets of requirements considerably limits system affordability. Conventional approaches to identifying these conflicts are either time efficient, yet ineffective, or effective, but time consuming. This paper proposes a novel method that sits between those extremes. It enables quick identification of conflicts, while still maintaining a good level of effectiveness. The proposed method, which is called the tension matrix, is built on three pillars: 1) heuristics to identify conflicting requirements, aimed at reducing completeness uncertainty; 2) targeted modeling; and 3) elemental decomposition. The effectiveness of the method was validated with a case study, on which a combination of retrospective assessment with a prospective analysis was employed. The results confirmed that the proposed tension matrix and the concept of elemental decomposition provide higher levels of effectiveness in identifying conflicting requirements, before initiating architectural or design activities, than conventional approaches.
Conventional approaches to system design use requirements as boundary conditions against which t... more Conventional approaches to system design use requirements as boundary conditions against which the design activity occurs. Decisions at a given level of the architecture decomposition can result in the flowing down of conflicting requirements, which are easy to fulfill in isolation but extremely difficult when dealt with simultaneously. Designing against such sets of requirements considerably limits system affordability. Identification of such conflicts is usually performed in industry by subject matter experts. Such evaluations are primarily driven by experience. As a result, effectiveness in identifying conflicting requirements is strongly dependent on the person making the assessment. We propose in this paper a set of heuristics that supports identification of conflicting requirements by providing direction and focus in the identification effort. The heuristics have been derived from a combination of literature review and experience from practitioners. In particular, a set of practitioners was interviewed orally and through a questionnaire in order to abstract and generalize their individual experiences.
Requirements are known as a key element in the success of a system and its development: they defi... more Requirements are known as a key element in the success of a system and its development: they define what a system is expected to do; more generally, they establish the boundaries of the problem to be solved. During elicitation a categorization template is usually employed in order to ensure completeness. The same categories are used during design in order to ease the understanding of the designers with respect to what needs to be achieved. In order to harmonize this process space agencies have standardized categorization models based on their heritage, being the ones developed by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) widely used. However, these categorization models present a major flaw: they do not fulfil the partition criterion. As a consequence, these categorization models facilitate the existence of overlapping requirements, which increases the necessary effort to manage and control requirements and increase the probability of inconsistent information. In addition, both models have been defined following a designer-perspective, i.e. requirements are organized according to design needs or attributes, and consequently they facilitate the elicitation of design-dependent requirements, which constraint (reduce) the solution space without satisfying new needs. The reduction in size of the solution space increases the difficulty to find better solutions and the time required to explore the solution space for a satisfactory solution. As a result, affordability is threatened. Would it be then possible to classify requirements differently so that they facilitate the elicitation of constraint-free specifications, thus promoting system affordability? The present research tests categorization models that fulfil the partition criterion as alternatives to traditional models and proves how they can support the elicitation of design-independent requirements for space systems and the identification of self-imposed constraints that do not support the satisfaction of new needs, or in other words, that maximize the solution space for a given amount of needs.
The architecting and development of systems of systems is highly complex. As a result, traditiona... more The architecting and development of systems of systems is highly complex. As a result, traditional methods based on point design approaches and detailed compliance analyses become highly ineffective. In addition, such approaches present a major drawback: it is impossible to know or even to assess with a sufficient level of confidence whether the projected solution lays within an optimal region in the solution space. Aiming at coping with complexity in a more effective manner when addressing systems of systems, this paper presents a 4-element framework that has been successfully applied to the architecting of the Space Weather System of Systems. In particular, the framework encompasses the following elements: (1) Architectural patterns were employed to define the set of potential architectures; (2) Morphological boxes were employed to define all instantiated architectures or system designs; (3) Tradespace exploration was employed to identify the Pareto frontier, i.e., the set of optimal solutions within the solution space; and (4) Normalisation of key requirements was employed to avoid regression to the mean flaws when performing comparative analyses between different architectures. In addition, this methodology was supported by simple system models and fast simulation tools, based on automating performance computation and architecture generation.
There is an increasing interest in Model-Based Systems Engineering (MBSE) practices in academia a... more There is an increasing interest in Model-Based Systems Engineering (MBSE) practices in academia and industry. The majority of research and adoption in industry is relevant to the early phases of the system life-cycle, where model-based design is expected to provide improved results during the system development. However, little attention has been paid to the application of such methodology to later phases of the development, and in particular to system integration and verification of the actual manufactured system, which continues to be done in the traditional document-centric environment. This paper proposes a model-centric environment for system integration and verification activities at the end of the development cycle and presents lessons learnt from its application to an actual space project.
Conventional approaches to system design use requirements as boundary conditions against which th... more Conventional approaches to system design use requirements as boundary conditions against which the design activity occurs. Decisions at a given level of the architecture decomposition can result in the flowing down of conflicting requirements, which are easy to fulfill in isolation but extremely difficult when dealt with simultaneously. Designing against such sets of requirements considerably limits system affordability. Existing research on the evaluation of such conflicts primarily seek to determine the level of conflicts between pairs of requirements. We assert in this paper that these methods are incomplete and using traditional methodologies can result in missing significant conflicts between groups of requirements. We provide a mathematical proof for this assertion and present two case studies that support the mathematical proof. We present the concept of “order of conflict.” The objective of this paper is to prove why pairwise-based conflicting requirements identification and analysis methods based on pairwise comparisons are flawed.
The present research suggests that the size of the solution space, which for a given set of stake... more The present research suggests that the size of the solution space, which for a given set of stakeholder needs is delimited by system requirements, relates to the probability of finding affordable solutions. As a result, the effectiveness of tradespace exploration techniques is limited by its size and internal ordering. Therefore, we suggest that there exist models to elicit and use requirements that, for a given set of stakeholder needs, could facilitate the maximization of the solution space so that the probability of finding more affordable solutions during tradespace exploration is also maximized. The present research proposes a mathematical model of the requirements elicitation process that facilitates defining performance objectives for the requirements elicitation process in striving for system affordability. The uniqueness of this research lays on two elements. First, the requirements elicitation process is mathematically modeled so that their objectives with respect to the effects on the solution space can be mathematically, and thus rigorously, described. Second, the system of interest focuses on the definition of the solution space as a driver for system affordability instead of on its actual exploration. The present research closes therefore the loop between stakeholder needs, system requirements, solution spaces, and system affordability. The results of the present research are generalized to discrete requirements, fuzzy requirements, and continuous requirements or value functions.
10th System of Systems Engineering Conference, 2015
A key element differentiating traditional systems from systems of systems is governance. While sy... more A key element differentiating traditional systems from systems of systems is governance. While systems are characterized by belonging to a single governing authority, systems within a system of systems are often independently governed or governed by fully empowered entities. Such independence is a necessary condition for the autonomy of each constituent system and for enabling the concept of belonging. At the same time, the capability to be autonomous and the voluntary nature of belonging, enables a constituent system to voluntarily abandon the system of systems it belongs to as well. Yet, research has not addressed so far the implications and modeling of intended abandonment into the operational effectiveness of a system of systems. This paper presents the concept of system abandonment as a philosophical necessity in the definition of systems of systems, it discusses some visions to measure the risk of abandonment, and proposes a way forward to explore mitigation techniques.
Requirement engineering is the cornerstone of systems engineering. Numerous large scale engineere... more Requirement engineering is the cornerstone of systems engineering. Numerous large scale engineered systems face schedule delays, cost overruns and performance shortfalls that can be traced back to the requirements they need to fulfill. In fact, previous research has demonstrated strong relationship between requirements and systems affordability. This paper summarizes and puts into context the authors’ novel contributions in three domains of requirements engineering: systems theory, complexity science, and systems methodologies. The authors propose new theorems and their proofs on requirements affecting affordability, propose a new complexity metric at requirement stage that measures the complexity limit of the system at conceptual stage (even before a specific design is determined), and propose two methodologies to elicit excess-free requirement sets and to identify conflicting requirements more effectively. The paper showcases the value of structuring a research in such a manner, i.e. from theory to practice, enabling strengthening the bounds between theorists and practitioners.
Systems engineering has been successfully applied to a wide variety of industries, which include... more Systems engineering has been successfully applied to a wide variety of industries, which include defense, space, energy, or transportation. All those systems have in common that they are engineered systems and/or socio-technical ones. Yet, systems engineering is considered both an art and a science. Therefore, could systems engineering be or have been applied in the domain of art, even if not done explicitly? Being one of the authors of this paper a systems engineer and the other one a music composer, this paper reports on the reflections of mutual discussions about how each of us of carried out our activities in our respective domain. Interestingly, it turns out that engineering a space system and creating a film original score abstractly follow the same set of principles and practices.
The term solution space is widely used in the engineering community; yet there is little known ab... more The term solution space is widely used in the engineering community; yet there is little known about their evolution. Theoretical research in the field of systems science indicates that requirements can only reduce the solution space. Yet, some authors state that on the contrary requirements can be used to expand to or open new solution spaces. Furthermore, some practitioners defend that the requirement to use a previously nonexistent technology would actually increase the solution space or move it to a new area, while others state that more requirements make life more difficult. Who is right then? The present paper provides initial answers to this question using systems theory. In order to achieve this, the present paper differentiates between various types of solutions spaces, which depend on the systems they include. Finally, the paper provides practical examples to showcase the results of the theoretical findings within real contexts.
Conventional approaches to system design use requirements as boundary conditions against which th... more Conventional approaches to system design use requirements as boundary conditions against which the design activity occurs. Decisions at a given level of the architecture decomposition can result in a flowing down of conflicting requirements, which are easy to fulfill in isolation but extremely difficult when dealt with simultaneously. Designing against such sets of requirements considerably limits system affordability. Conventional approaches to identifying these conflicts are either time efficient, yet ineffective, or effective, but time consuming. This paper proposes a novel method that sits between those extremes. It enables quick identification of conflicts, while still maintaining a good level of effectiveness. The proposed method, which is called the tension matrix, is built on three pillars: 1) heuristics to identify conflicting requirements, aimed at reducing completeness uncertainty; 2) targeted modeling; and 3) elemental decomposition. The effectiveness of the method was validated with a case study, on which a combination of retrospective assessment with a prospective analysis was employed. The results confirmed that the proposed tension matrix and the concept of elemental decomposition provide higher levels of effectiveness in identifying conflicting requirements, before initiating architectural or design activities, than conventional approaches.
Conventional approaches to system design use requirements as boundary conditions against which t... more Conventional approaches to system design use requirements as boundary conditions against which the design activity occurs. Decisions at a given level of the architecture decomposition can result in the flowing down of conflicting requirements, which are easy to fulfill in isolation but extremely difficult when dealt with simultaneously. Designing against such sets of requirements considerably limits system affordability. Identification of such conflicts is usually performed in industry by subject matter experts. Such evaluations are primarily driven by experience. As a result, effectiveness in identifying conflicting requirements is strongly dependent on the person making the assessment. We propose in this paper a set of heuristics that supports identification of conflicting requirements by providing direction and focus in the identification effort. The heuristics have been derived from a combination of literature review and experience from practitioners. In particular, a set of practitioners was interviewed orally and through a questionnaire in order to abstract and generalize their individual experiences.
Requirements are known as a key element in the success of a system and its development: they defi... more Requirements are known as a key element in the success of a system and its development: they define what a system is expected to do; more generally, they establish the boundaries of the problem to be solved. During elicitation a categorization template is usually employed in order to ensure completeness. The same categories are used during design in order to ease the understanding of the designers with respect to what needs to be achieved. In order to harmonize this process space agencies have standardized categorization models based on their heritage, being the ones developed by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) widely used. However, these categorization models present a major flaw: they do not fulfil the partition criterion. As a consequence, these categorization models facilitate the existence of overlapping requirements, which increases the necessary effort to manage and control requirements and increase the probability of inconsistent information. In addition, both models have been defined following a designer-perspective, i.e. requirements are organized according to design needs or attributes, and consequently they facilitate the elicitation of design-dependent requirements, which constraint (reduce) the solution space without satisfying new needs. The reduction in size of the solution space increases the difficulty to find better solutions and the time required to explore the solution space for a satisfactory solution. As a result, affordability is threatened. Would it be then possible to classify requirements differently so that they facilitate the elicitation of constraint-free specifications, thus promoting system affordability? The present research tests categorization models that fulfil the partition criterion as alternatives to traditional models and proves how they can support the elicitation of design-independent requirements for space systems and the identification of self-imposed constraints that do not support the satisfaction of new needs, or in other words, that maximize the solution space for a given amount of needs.
The architecting and development of systems of systems is highly complex. As a result, traditiona... more The architecting and development of systems of systems is highly complex. As a result, traditional methods based on point design approaches and detailed compliance analyses become highly ineffective. In addition, such approaches present a major drawback: it is impossible to know or even to assess with a sufficient level of confidence whether the projected solution lays within an optimal region in the solution space. Aiming at coping with complexity in a more effective manner when addressing systems of systems, this paper presents a 4-element framework that has been successfully applied to the architecting of the Space Weather System of Systems. In particular, the framework encompasses the following elements: (1) Architectural patterns were employed to define the set of potential architectures; (2) Morphological boxes were employed to define all instantiated architectures or system designs; (3) Tradespace exploration was employed to identify the Pareto frontier, i.e., the set of optimal solutions within the solution space; and (4) Normalisation of key requirements was employed to avoid regression to the mean flaws when performing comparative analyses between different architectures. In addition, this methodology was supported by simple system models and fast simulation tools, based on automating performance computation and architecture generation.
There is an increasing interest in Model-Based Systems Engineering (MBSE) practices in academia a... more There is an increasing interest in Model-Based Systems Engineering (MBSE) practices in academia and industry. The majority of research and adoption in industry is relevant to the early phases of the system life-cycle, where model-based design is expected to provide improved results during the system development. However, little attention has been paid to the application of such methodology to later phases of the development, and in particular to system integration and verification of the actual manufactured system, which continues to be done in the traditional document-centric environment. This paper proposes a model-centric environment for system integration and verification activities at the end of the development cycle and presents lessons learnt from its application to an actual space project.
Conventional approaches to system design use requirements as boundary conditions against which th... more Conventional approaches to system design use requirements as boundary conditions against which the design activity occurs. Decisions at a given level of the architecture decomposition can result in the flowing down of conflicting requirements, which are easy to fulfill in isolation but extremely difficult when dealt with simultaneously. Designing against such sets of requirements considerably limits system affordability. Existing research on the evaluation of such conflicts primarily seek to determine the level of conflicts between pairs of requirements. We assert in this paper that these methods are incomplete and using traditional methodologies can result in missing significant conflicts between groups of requirements. We provide a mathematical proof for this assertion and present two case studies that support the mathematical proof. We present the concept of “order of conflict.” The objective of this paper is to prove why pairwise-based conflicting requirements identification and analysis methods based on pairwise comparisons are flawed.
The present research suggests that the size of the solution space, which for a given set of stake... more The present research suggests that the size of the solution space, which for a given set of stakeholder needs is delimited by system requirements, relates to the probability of finding affordable solutions. As a result, the effectiveness of tradespace exploration techniques is limited by its size and internal ordering. Therefore, we suggest that there exist models to elicit and use requirements that, for a given set of stakeholder needs, could facilitate the maximization of the solution space so that the probability of finding more affordable solutions during tradespace exploration is also maximized. The present research proposes a mathematical model of the requirements elicitation process that facilitates defining performance objectives for the requirements elicitation process in striving for system affordability. The uniqueness of this research lays on two elements. First, the requirements elicitation process is mathematically modeled so that their objectives with respect to the effects on the solution space can be mathematically, and thus rigorously, described. Second, the system of interest focuses on the definition of the solution space as a driver for system affordability instead of on its actual exploration. The present research closes therefore the loop between stakeholder needs, system requirements, solution spaces, and system affordability. The results of the present research are generalized to discrete requirements, fuzzy requirements, and continuous requirements or value functions.
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Papers by Alejandro Salado