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Background: The Systems Engineering and Software Engineering disciplines are highly intertwined in most modern Systems of Systems (SoS), and particularly so in industries such as defense, transportation, energy and health care. However, the combination of these disciplines during the architecting of SoS seems to be especially challenging; the literature suggests that major integration and operational issues are often linked to ambiguities and gaps between system-level and software-level architectures. Aims: The objective of this paper is to empirically investigate: 1) the state of practice on the interplay between these two disciplines in the architecting process of systems with SoS characteristics; 2) the problems perceived due to this interplay during said archi-tecting process; and 3) the problems arising due to the particular characteristics of SoS systems. Method: We conducted a questionnaire-based online survey among practitioners from industries in the aforementioned domains, having a background on Systems Engineering, Software Engineering or both, and experience in the architecting of systems with SoS characteristics. The survey combined multiple-choice and open-ended questions, and the data collected from the 60 respondents were analyzed using quantitative and qualitative methods. Results: We found that although in most cases the software archi-tecting process is governed by system-level requirements, the way requirements were specified by systems engineers, and the lack of domain-knowledge of software engineers, often lead to misinterpretations at software level. Furthermore, we found that unclear and/or incomplete specifications could be a common cause of technical debt in SoS projects, which is caused, in part, by insufficient interface definitions. It also appears that while the SoS concept has been adopted by some practitioners in the field, the same is not true about the existing and growing body of knowledge on the subject in Software Engineering resulting in recurring problems with system integration. Finally, while not directly related to the interplay of the two disciplines, the survey also indicates that low-level hardware components, despite being identified as the root cause of undesired emergent behavior, are often not considered when modeling or simulating the system. Conclusions: The survey indicates the need for tighter collaboration between the two disciplines, structured around concrete guidelines and practices for reconciling their differences. A number of open issues identified by this study require further investigation.
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A Survey on the Interplay between Soware Engineering and
Systems Engineering during SoS Architecting
Héctor Cadavid
University of Groningen
Groningen, the Netherlands
Vasilios Andrikopoulos
University of Groningen
Groningen, the Netherlands
Paris Avgeriou
University of Groningen
Groningen, the Netherlands
John Klein
Gloucester, Massachusetts
The Systems Engineering and Software Engineer-
ing disciplines are highly intertwined in most modern Systems of
Systems (SoS), and particularly so in industries such as defense,
transportation, energy and health care. However, the combination
of these disciplines during the architecting of SoS seems to be es-
pecially challenging; the literature suggests that major integration
and operational issues are often linked to ambiguities and gaps
between system-level and software-level architectures.
The objective of this paper is to empirically investigate: 1)
the state of practice on the interplay between these two disciplines
in the architecting process of systems with SoS characteristics;
2) the problems perceived due to this interplay during said archi-
tecting process; and 3) the problems arising due to the particular
characteristics of SoS systems.
We conducted a questionnaire-based online survey among
practitioners from industries in the aforementioned domains, hav-
ing a background on Systems Engineering, Software Engineering
or both, and experience in the architecting of systems with SoS
characteristics. The survey combined multiple-choice and open-
ended questions, and the data collected from the 60 respondents
were analyzed using quantitative and qualitative methods.
We found that although in most cases the software archi-
tecting process is governed by system-level requirements, the way
requirements were specied by systems engineers, and the lack of
domain-knowledge of software engineers, often lead to misinter-
pretations at software level. Furthermore, we found that unclear
and/or incomplete specications could be a common cause of tech-
nical debt in SoS projects, which is caused, in part, by insucient
interface denitions. It also appears that while the SoS concept has
been adopted by some practitioners in the eld, the same is not true
Also with Escuela Colombiana de Ingeniería.
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about the existing and growing body of knowledge on the subject in
Software Engineering resulting in recurring problems with system
integration. Finally, while not directly related to the interplay of the
two disciplines, the survey also indicates that low-level hardware
components, despite being identied as the root cause of undesired
emergent behavior, are often not considered when modeling or
simulating the system.
The survey indicates the need for tighter collabo-
ration between the two disciplines, structured around concrete
guidelines and practices for reconciling their dierences. A number
of open issues identied by this study require further investigation.
Software and its engineering Software architectures
large-scale systems.
systems of systems, architecting, practitioners survey
ACM Reference Format:
Héctor Cadavid, Vasilios Andrikopoulos, Paris Avgeriou, and John Klein.
2020. A Survey on the Interplay between Software Engineering and Systems
Engineering during SoS Architecting. In ESEM ’20: ACM / IEEE International
Symposium on Empirical Software Engineering and Measurement (ESEM)
(ESEM ’20), October 8–9, 2020, Bari, Italy. ACM, New York, NY, USA, 11 pages.
The concept of System of Systems (SoS) is used across applica-
tion domains like defense, automotive, energy and health care to
describe a family of systems that cooperate to provide new capabil-
ities [
]. Strictly speaking, most systems could be considered as
SoS, since they can be decomposed into smaller subsystems [
however, the engineered SoS — in contrast to a naturally occurring
one like an ecosystem — is often distinguished by some degree
of operational and managerial independence of its constituents, as
proposed by Maier’s seminal paper [
]. The SoS paradigm is of
strategic importance in industry, as it promotes the cooperation
among already operational systems towards the delivery of new
capabilities [5].
The architecting process of an SoS, compared with other en-
gineered systems, must address a unique set of challenges. For
ESEM ’20, October 8–9, 2020, Bari, Italy Cadavid, et al.
instance, architecting an SoS involves the adaptation and integra-
tion of existing and usually heterogeneous independent systems as
constituent systems of the SoS. Such integration should enable the
fulllment of the SoS mission or capabilities through cooperation
between its constituent systems [
]. However, those constituent
systems are fundamentally independent, and their own needs must
also be balanced with the needs of the SoS that they are integrated
into [
]. At the same time, the architecting process of most modern
engineered SoS must follow the complementary perspectives of
two related but distinct disciplines: Systems Engineering (SE) and
Software Engineering (SWE). Historically, the development of SoS
has usually been driven by SE processes [
] due to the integration
of physical (e.g. mechanical, electronic) constituent systems. How-
ever, software is now not only pervasive and abundant, but also a
critical element of the performance and features oered by most
modern engineered systems [17, 35].
Unfortunately, the interplay between the two disciplines has
proven problematic. Integration and operational problems in SoS
are often linked to inconsistencies or gaps between the system-level
and the software-level architectural elements created, respectively,
by these two disciplines [
]. This seems to be a consequence of
the way SE and SWE have evolved over time: starting with common
roots but becoming misaligned due to their separate evolutionary
paths [
]. The dierences in their approaches make the architec-
ture perspectives dicult to synchronize, and as Sheard et al. [
reported, these dierences can interfere with each discipline’s prac-
tices. For example, in a project using a SE decomposition approach,
the design and development of the software components of the sys-
tem may become distributed across several physical sub-systems
and assigned to independent development teams or contractors. In
that case, the architectural concerns of the system (e.g. performance,
reliability, security) would be dicult to address in a unied way
at the software level.
The need to reconcile the SE and SWE disciplines has driven a
number of initiatives to integrate them at a development process
level. For instance, the ISO 15288 standard for SE processes [
] in-
cludes suggestions for its integration with ISO 12207-compliant [
SWE processes. However, most methodologies and guidelines tai-
lored for SoS are mostly SE-centered and lack guidelines for the
integration of SWE architecting practices. Prominent examples of
such methodologies and guidelines are the Systems Engineering
Guide for SoS [
], the ISO/IEC 21839 standard [
], and the results
of the FP7
projects DANSE [
] and AMADEOS [
Nevertheless, none of these approaches prescribes practices to align
software-level with system-level architectures, as they consider
software as just another type of constituent system and not as a
cross-cutting element of an SoS.
Therefore, to contribute to the improvement of the architecting
processes of engineered SoS, we believe it is important to address
the problems posed by the interplay between SWE and the SE dis-
ciplines. There is little up-to-date evidence about these problems in
‘traditional’ engineered systems, and to the best of our knowledge,
no evidence at all for the particular case of SoS. This work addresses
this gap by identifying, from the perspective of practitioners from
Seventh framework programme of the European Commission for research and tech-
nological development including demonstration activities
both disciplines, the challenges that arise from the interplay of these
two disciplines when architecting systems with SoS characteristics.
To this end, this paper reports on the design, execution and main
ndings of an online survey of practitioners working on complex
systems with SoS characteristics that took place between December
2019 and February 2020.
The rest of this paper is structured as follows: Section 2 summa-
rizes the state of the art on the interplay between SE and SWE in
and out of the context of SoS systems. Section 3 presents the design
of the practitioner survey, and Section 4 summarizes its results. Sec-
tion 5 discusses the relevance of our ndings for practitioners and
researchers, and outlines open issues for further research. Finally,
Section 6 concludes this study.
The interplay between SE and SWE in the context of SoS archi-
tecting has not been widely studied. We found only two studies
exploring this issue, each focused on a particular scenario. Boehm
et al. [8] focused on the acquisition and integration of constituent
systems, and proposed an approach to address the problem of un-
derperforming SE in the domain of defense caused by the traditional
hardware-centered systems engineering and subsystem acquisition
practices. Gagliardi et al. [
] proposed an evaluation method for
SoS and software architectures to address the problem of lack of
attention of quality attributes caused by the diversity of notations
used for system and software elements of SoS.
Beyond the context of architecting in the specic domain of
SoS, there is related work exploring the problems between these
two disciplines in general and specic interdisciplinary problems
in the architecting process of systems. Here, we provide a brief
description of both categories. In one of the earliest works in the
rst category, Sommerville [
] pointed out how failed case studies
like the DIA Baggage System [
] were caused not only by soft-
ware problems, but by how software was integrated in the systems
engineering process. He proposed the introduction of systems en-
gineering concepts in computer science courses as an approach
to tackle this integration problem. Much later, Fairley et al. [
discussed how software engineers’ lack of qualications on SE con-
cepts limited their participation in system-level decision making.
Like Sommerville, they proposed to address this problem at its
roots by integrating SWE topics in SE curricula. This, and Fair-
leys’s follow-up works on alternative development models for SE
and SWE process articulation, led to the recently published book
Systems-Engineering for Software-enabled systems [17].
In the second category of related work, Maier’s paper on System
and Software Architecture reconciliation [
] is one of the earliest
studies that takes an architectural perspective on the SE-SWE inter-
relation problem. In this work, which later would become part of The
art of systems architecting book [
], Maier pointed out the problems
caused by mismatches between the architectural structures used by
the traditional, hardware-centered systems engineering and those
used by modern software engineering.
In recent years, INCOSE
has promoted an empirical approach
to tackle the problems between these two disciplines. For instance,
Pyster et al. [
] reported on a workshop co-sponsored by INCOSE
2International Council on Systems Engineering
A Survey on the Interplay between Soware Engineering and Systems Engineering during SoS Architecting ESEM ’20, October 8–9, 2020, Bari, Italy
with 29 professionals from academia and industry described as a
“cross section of systems and software engineering community”,
held to identify said problems, and the challenges created by them.
Subsequently, INCOSE approved the charter of the Systems and
Software Interface Working group (SaSIWG), and recently published
a series of problem-related ndings identied through its members
interaction [39, 40].
3.1 Study goal and research questions
The goal of this study is to identify the problems related to the
interplay between SE and SWE disciplines during SoS architecting
in practice. We used the ve parameters proposed by the Goal-
Question-Metric (GQM) goal template [6] for a precise denition:
the architecting process of complex engineered systems
with SoS characteristics
for the purpose
of collecting and
characterizing the perceived challenges
with respect to
the in-
terplay between the Systems and Software Engineering disciplines
from the viewpoint of
experts with practical experience and
background in Systems Engineering, Software Engineering or
in the context of
application domains where said inter-
play takes place such as defense, energy, transportation and health.
The rst parameter — the Object under study, focuses on sys-
tems with SoS characteristics, rather than systems self-identied
as SoS; this is because of the unclear boundaries of SoS as a con-
cept. For instance, not all systems that present SoS characteristics
self-identify with this label [
]; some adopt a related term (e.g.
Cyber-Physical Systems or Software-intensive Systems [
]). This
could be due to the debate regarding whether an SoS is a distinct
class of systems [
], or whether it is an optional viewpoint for
complex systems [
]. On the other hand, there are many cases of
mis-classifying systems as SoS, as noted by Maier [
]. This prob-
lem is suggested, for example, by the way SoS as a concept is used in
some secondary studies in the eld [
], with no references to any
of the multiple existing denitions or sets of characteristics [
As a way to deal with these semantic ambiguities, we instead adopt
the SoS characteristics from Firesmith’s model [
] to classify the
systems used as reference for this study (see Section 3.2.1):
Constituent System Autonomy
The degree to which the con-
stituents are operationally independent, i.e. with a purpose of
their own.
Constituent System Governance
The degree to which the con-
stituents are managed, owned or operated by a higher-level au-
Constituent System Heterogeneity
The degree to which the
constituents dier from each other in terms of functionality or
Constituent System Physical distribution
The degree to which
the constituents exist in geographically disperse locations.
SoS Complexity
The degree to which the SoS is dicult to un-
derstand and analyze.
SoS Evolution
The degree to which the SoS requirements change
over time.
SoS Emergence
The degree to which desired or undesired be-
haviors emerge from the cooperation between the constituent
Based on the goal described above, we dened the following
research questions:
What challenges do practitioners face as a consequence of the
interplay between the Software Engineering and Systems
Engineering disciplines during SoS architecture analysis,
synthesis and evaluation?
What challenges do practitioners face in SoS architecting
when dealing with the emergent behavior of SoS, and the
autonomy of their constituent systems (ConS)?
The rst research question (RQ1) seeks to identify the problems
faced by practitioners due to the mismatches between the SE and
SWE disciplines in the architecting process of an SoS. Specically,
we adopt the reference architecting process of Hofmeister et al. [
which considers three activities: (1) analysis—dealing with system
requirements, (2) synthesis—the way architectural decisions are
taken, and (3) evaluation of such architectural decisions. We con-
sider each of these three activities from the standpoint of both
systems and software engineering. The second research question
(RQ2), aims to identify relevant challenges in the architecting pro-
cess explicitly linked to two of the SoS characteristics: emergent
behavior and autonomy of the constituents of the system. We have
selected these two as they are the most distinctive characteristics
of SoS [21, 28].
3.2 Research method
To answer the research questions, we conducted a questionnaire-
based survey to collect insights from practitioners with experience
in the architecting of systems with SoS characteristics. The survey
research method was selected because the research questions re-
quire a broad overview of the studied object (architecting of systems
with SoS characteristics) and examination of knowledge, attitudes
and behaviors related to it (interdisciplinary problems experienced
by practitioners) [
]. More specically, we use the online survey
method to obtain information from as wide a sample as possible
from the population of practitioners and researchers with prac-
tical experience. We adopted the guidelines of Kitchenham and
Peeger [25] and followed the prescribed steps:
(1) Setting the objectives, as described in Section 3.1.
(2) Designing the survey.
(3) Developing the survey instrument.
(4) Obtaining valid data.
(5) Analyzing the data.
3.2.1 Survey design and development. The questionnaire designed
for this study has 24 questions, which include both multiple-choice
and open-ended questions, divided into three sets. The rst set
focuses on the background of the respondents, and it is included to
characterize the demographics of the survey sample. The second
set begins by asking respondents to think about the most complex
system they have been involved in the last 10 years. That system
will be used as a reference to answer the rest of the questions in
the survey. The questions in the second set focus on identifying
ESEM ’20, October 8–9, 2020, Bari, Italy Cadavid, et al.
the characteristics of the selected system and the disciplines, ap-
proaches and terms used in the corresponding project. To prole
the selected system in terms of the SoS characteristics discussed in
Section 3.1, questions in this set used a slider widget to allow to
allow respondents to select a continuous value between 0 and 5 for
each characteristic. The third and nal set of questions collect data
about the architecture practices used and problems observed by the
respondent while working on the selected system. The complete
questionnaire is available in the study replication package
. This is
the version of the questionnaire that was actually used for the sur-
vey, following a few iterations of pilot studies for its improvement,
as discussed further in Section 3.3.
3.2.2 Obtaining data. The survey was developed and distributed
through the Qualtrics.XM platform [
]. The target population of
this study was experts with a background in Software Engineering,
Systems Engineering or both, who have been involved in engineer-
ing projects for systems with SoS characteristics. This background
and experience makes the target population rather specic; hence,
it is not trivial to obtain a representative sample. Consequently, we
followed a non-probabilistic sampling that combined convenience
and snowballing sampling [
]. More specically, an invitation to
participate and to further disseminate the survey was distributed
by email across the personal networks of the authors to contacts
who worked in industries like the ones mentioned in the study goal.
In addition, the survey was promoted through posts on relevant
LinkedIn groups and other social media platforms, the mailing list
of INCOSE’s Systems and Software-Interface working group which
had 54 members, and through publicity iers at the INCOSE’s Inter-
national Workshop (held on January 25th/2020). Moreover, the rst
author manually searched for publicly available email addresses of
practitioners who were likely to t the inclusion criteria, based on
LinkedIn prole and group membership information. As a result,
281 additional contacts were identied and then invited to partici-
pate in the survey, through a series of personalized emails which
described the survey, the average completion time, and linked to the
questionnaire itself. Two follow-up reminder messages were sent to
the potential respondents between mid-January and mid-February,
2020. This resulted in a total of 76 responses.
3.2.3 Analyzing the data. The data obtained from the survey were
analyzed with a combination of quantitative and qualitative meth-
ods. The responses to the open-ended questions were analyzed
using Qualitative Content Analysis (QCA) [16] following an induc-
tive approach, which involved open coding, creating categories,
and abstraction. The responses to closed-ended questions, on the
other hand, were analyzed following quantitative analysis meth-
ods, including data visualization and statistical analysis [
]. More
specically, descriptive statistics, including frequencies and per-
centages, were used to describe the characteristics of the sample,
and the relationships between the variables. Since there were no
hypotheses to test, no statistical testing was employed.
3.3 Threats to validity
In the following we discuss the perceived threats to the validity of
this study and the steps taken to mitigate them. We use Runeson
and Höst [
] as a guide for this purpose. We note that, as the
nature of this study is exploratory and did not investigate causal
relationships, it is not subject to internal validity threats.
Construct validity. Construct validity refers to the degree to
which the operational measures, in this case the online survey,
reect what the researchers have in mind and are consistent with
the research questions. To improve the validity of the study in this
respect, we piloted two consecutive versions of the survey, each
with a dierent set of respondents, for a total of 7 respondents.
These respondents were selected according to the survey goal (see
Section 3.1), and could be described as experienced practitioners
and researchers with background in Systems Engineering (3), and
both Systems Engineering and Software Engineering (4). The pilot
survey respondents provided key feedback on the wording and the
consistency of the questions, particularly the ones that involved
Systems Engineering-related terms. This allowed us to minimize
potential miscommunication issues. The authors have also itera-
tively rened the study design to ensure that all aspects of the study
were clear prior to commencing the survey.
External validity. External validity is concerned with the degree
to which the ndings can be generalized from the sample to the
population. The non-probabilistic sampling design used for data
collection is a potential threat for the external validity of the study.
For instance, there is a risk of a biased sample, which is not represen-
tative of the target population, or with a dominant participation of
a certain sector. To mitigate this threat, the survey was distributed
not only through the personal networks of the authors, but also
through organizations and social media platforms that address sys-
tems and software engineers from dierent application domains.
The demographic information of the participants reported in Sec-
tion 4.1, including the application areas of the organization they
belong to, attests to the representativeness of our sample. However,
we also have to acknowledge that our ndings cannot be general-
ized beyond the population our sample represents, e.g. in systems
that do not exhibit SoS characteristics or in application domains
outside those in Fig. 3.
Reliability. Reliability refers to the extent the data and the anal-
ysis are dependent on the specic researchers. The mature and
generally-accepted guidelines dened by Kitchenham and Peeger [
were followed for this purpose; the analysis of the respondents’
responses can also be veried externally by means of the available
replication package. Given the exploratory nature of this study, we
did not use advanced statistics-based analysis approaches; instead,
we used a combination of quantitative and qualitative methods.
To mitigate researcher bias in this process, three of the four au-
thors were involved in the quantitative data analysis for consensus-
building purposes; these authors also came to an agreement about
the interpretations drawn from the analysis. Finally, the same au-
thors were involved in the qualitative data analysis: the rst author
performed it using the QCA methodology [
], while its outcome
was validated for consistency by the other two.
A Survey on the Interplay between Soware Engineering and Systems Engineering during SoS Architecting ESEM ’20, October 8–9, 2020, Bari, Italy
14 12
Number of projects
Years of experience
Years of experience
14 12
Number of projects
Figure 1: Right: years of experience of the respondents. Le:
number of engineering projects respondents worked on
Figure 2: Distribution of the selected engineering practice
areas across the survey respondents as an Euler diagram
4.1 Demographics
A total of 76 responses were collected between December 20, 2019
and February 25, 2020. From this initial data set, 16 responses were
excluded before proceeding with the analysis: 15 responses were
incomplete and 1 response was from a respondent that indicated
zero years and projects as experience. Hence, the nal data set
contains 60 responses from practitioners with a mean of 20.8 years
of experience who have participated on average in 24.4 engineering
projects, shown in Fig. 1. Three outlier respondents claimed expe-
rience of more than 90 projects each, which makes the standard
deviation of the number of projects nearly double that of the years
of experience (22.8 vs 11.19).
Figure 2 shows the engineering practice areas of the respondents.
The areas most frequently reported were Systems Engineering (73%)
and Software Engineering (65%). Respondents were able to select
more than one practice area. The Euler diagram shows that a to-
tal of 57 respondents (95%) identied themselves as Systems Engi-
neers (30%), Software Engineers (22%) or both (43%). The remaining
3 respondents, added areas related to systems or software engi-
neering, as entries in ‘Other’: Computer systems designer,Software
Systems Engineering and Software-reliant Systems Engineering. All
the selected responses came from practitioners that t the target
population described in the study goal.
The respondents’ organizational aliations are shown in the top
part of Fig. 3. Multiple selections were allowed. Many respondents
(78%) identied with companies. Fewer respondents (around 20%)
also identied their organizations as research institutes, universi-
ties, or government agencies. The bottom part of Fig. 3, shows the
application areas of the respondents’ organizations. The results of
this survey are representative of domains such as transportation
0 5 10 15 20 25 30 35 40 45 50
Consumer Products
Disaster Recovery
Figure 3: Organizations that respondents are aliated with.
Top: organization type; Boom: application areas of the or-
Figure 4: Distribution of project characteristics as violin plot
(48%), defense (45%), energy (30%) and manufacturing (25%). This
aligns with the study’s context: application domains where SoS ar-
chitecting requires an interplay between the systems and software
engineering disciplines.
4.2 Reference projects
As described in Section 3.2.1, respondents were asked to select a ref-
erence system to complete the survey and prole the characteristics
of that system. Figure 4 shows the distribution of response values for
each characteristic. Values for the Size, Complexity and Heterogene-
ity characteristics show that the sample of systems explored in this
study represents large, highly complex systems, whose constituents
are very heterogeneous. The response values for the Emergence,
Governance and Autonomy characteristics are spread throughout
the value range, indicating projects with dierent degrees of control
on the constituent systems.
Respondents were also asked whether the selected project self-
identied its system as a System of Systems. Of the 60 responses, 37
used the label ‘SoS’ to describe the system, whereas 23 used other
terms such as Complex System,Software Intensive System and Em-
bedded System.
However, by comparing the distribution of the
characteristics of the systems that self-identify as SoS with
the ones that do not, shown in Fig. 5, there are only minor
ESEM ’20, October 8–9, 2020, Bari, Italy Cadavid, et al.
Figure 5: Distribution of project characteristics: systems self-
identied as SoS vs. not self-identied ones
dierences (Finding 1)
, and they appear mostly in the distribu-
tions of Size,Evolution and Complexity values. This appears to
justify our decision to survey practitioners irrespective of whether
they use the term ‘SoS’ for their systems, and instead focus on
ensuring the presence of SoS characteristics.
Furthermore, it is worth noting that out of the 37 systems self-
identied as SoS, only 10 applied well-known SoS-specic guide-
lines (e.g. DoD guidelines for SoS [
] or the ISO/IEC/IEEE 21839–
40 [
]), and none made reference to any of the guidelines or frame-
works proposed, in recent years, by research in the eld of SoS
(e.g. [
This suggests a low adoption by practitioners of
SoS-specic guidelines, and an even lower adoption of the
research produced in the domain of SoS (Finding 2).
4.3 Questions related to RQ1
4.3.1 Requirements at system and soware level. Q 3.1 of the sur-
vey, which focused on the architecting phase of Analysis, asked
respondents how system-level requirements and software-level re-
quirements were related to each other in the system selected by them
during the second set of questions (see Section 3.2.1). The responses
are summarized in Table 1. In most cases, software-level require-
ments are linked to system requirements (71%), either by being
explicitly derived from them (39%) or based partially on them (32%).
Figure 6, however, shows that there are no signicant dierences in
the characteristics between the systems developed following each
approach. It appears that the choice of approach is not related to
the characteristics of the system; further investigation is necessary.
In a follow-up question, respondents were asked an open-ended
question about the problems posed by the way system-level and
software-level requirements were related to each other. Six codes
emerged as the most prominent ones after applying QCA to the
responses. Two of the most frequent codes, Teams Coordination
Challenges and Assumptions About Other Disciplines, seem to
be related, in the sense that the former could be reinforcing the latter.
That is to say, due to the challenges of coordination and communi-
cation between interdisciplinary teams, there could be assumptions
Table 1: Frequency of the responses given to Q 3.1: relation
of system– and software–level requirements
Response Frequency
Software-level requirements were derived from system-
level requirements
Software-level requirements were elicited by taking into
consideration, among others, system-level requirements
Software-level and system-level requirements were elicited
independently by separate teams
Software-level and system-level requirements were elicited
simultaneously by the same team
Other 6
Figure 6: System characteristics of the two most common re-
sponses to Q 3.1
about how the other party would address the requirements, instead
of agreements. Incomplete System Reqirements (which includes
vague or poorly documented requirements) and Lack of Domain
Knowledge from the Software Engineers correspond to the prob-
lems that lead to misinterpretation of system-level requirements
at the software architecture level.
These two problems (incom-
plete systems requirements and lack of domain knowledge)
are particularly important: for most of the systems consid-
ered in this survey, software-level requirements are derived
from or based on system-level requirements (Finding 3)
, as
discussed above. The remaining two codes are Lack of System-
level Perspective by the teams and organizations involved, and
perhaps even more interestingly Interdisciplinary Differences
resulting in conicting or over-restrictive requirements coming
from the system level.
4.3.2 Architectural decisions at system and soware level. Q 3.2,
related to the architecting activity of Synthesis, asked respondents
how the architectural decisions were taken for the selected project,
at system and software level. Table 2 shows that most of the re-
sponses (77%) are nearly evenly distributed between two oppo-
site approaches: Decisions are taken separately by independent
A Survey on the Interplay between Soware Engineering and Systems Engineering during SoS Architecting ESEM ’20, October 8–9, 2020, Bari, Italy
Table 2: Frequency of the responses given to Q 3.2: how were
architectural decisions at dierent levels taken
Response Frequency
System-level and software-level architectural decisions
were taken independently, by separate teams
System-level and software-level architectural decisions
were taken, together, by the same team
Architectural decisions were taken at system level only
(there was no intentionally designed software architecture)
Other 10
systems-engineering and software engineering teams (41%), or
taken together by an interdisciplinary team (36%).
The high ratio
of systems where architectural decisions were taken inde-
pendently by teams from the two disciplines is noteworthy,
because intuitively, decisions taken independently could be
problematic in many cases. (Finding 4)
Q 3.3 asked about the problems posed by the way architectural
decisions were taken at both system and software level. Applying
QCA to the responses shows that the most common problems can
be classied as related to: integration (70% of responses in total),
documentation (53%) and operation (43%). The problems reported
by the respondents as ‘Other’ and coded as Unsatisfied reqire-
ments and Bugs/issues caused by under-scrutinized complex
interactions were counted as operation-related problems, and
included in the above percentage. Likewise, Third-party compo-
nents inconsistencies and Poor documentation, also reported
by the respondents as other problems, were counted as integration
and documentation-related problems, respectively. An observation
that requires further investigation is that respondents that selected
both the SE and SWE practice areas report more problems with
the architectural decisions (49% of all cases reported) compared
to respondents with other backgrounds. It may be that their un-
derstanding and experience in both practice areas allows them to
diagnose issues that otherwise would go unnoticed until much later;
this is the subject for a separate, future study.
Another observation is that
both of the most frequently re-
ported approaches for making architectural decisions, i.e. in
separate or interdisciplinary mixed teams, report a very high
rate of integration problems (Finding 5)
. As shown in Fig. 7,
both approaches report similar frequency of documentation prob-
lems, but surprisingly operational problems were reported for only
33% of systems where teams from dierent disciplines worked sep-
arately, compared to 48% of systems using interdisciplinary teams.
This may be simply due to reduced visibility of the overall opera-
tional situation in compartmentalized teams.
4.3.3 Architecture evaluation at system and soware level. The ques-
tions related to the architecting activity of Evaluation asked how
system-level (Q 3.4) and software-level (Q 3.5) architectural decisions
were evaluated with respect to functional and non-functional require-
ments, and what problems were posed by combining these two eval-
uation approaches (Q 3.6). The responses to Q 3.4, summarized in
Table 3, show that simulations and prototyping were the most
Figure 7: Problems reported given the approach followed for
architectural decision making, normalized (Q 3.3)
Table 3: Frequency of the responses given to Q 3.4: evalua-
tion of architectural decisions at system level
Response Frequency
Simulation-based evaluation 21
Prototype-based evaluation 17
Evaluation in production 16
Formal/mathematical evaluation 11
The architectural decisions were not evaluated 4
Do not know 7
Other 14
Table 4: Frequency of the responses given to Q 3.5: evalua-
tion of architectural decisions at software level
Response Frequency
Software architecture was evaluated against the system re-
quirements, after the system requirements and architecture
were established
Software architecture was considered as implicitly evalu-
ated by the the system architecture validation
Software architecture was evaluated evaluated against a
set of requirements that are not related to the system re-
There was no architecture evaluation in the project 4
Do not know 9
Other 8
frequently reported approaches for system-level architectural de-
cision evaluation. The responses to Q 3.5, summarized in Table 4,
on the other hand, show that in most cases (53%), the evaluation
of software-related architectural decisions were subordinated to
the system-level architecture: The evaluation was either based on
system-level requirements (33%), or considered as implicitly evalu-
ated by the system-level architecture validation (20%).
related architectural decisions, from the evaluation stand-
point, appear to have lower priority compared to the system-
related decisions. (Finding 6)
From these results, it is also worth
noting that approaches that would be expected to be more frequent,
such as the scenarios-based [
] ones, were mentioned as Other
approaches by a limited amount of respondents.
In the Euler diagram of Fig. 8, there appear two phenomena on
how the dierent system-level evaluation approaches were com-
bined. First, for 17% of the systems, the system-level architectural
ESEM ’20, October 8–9, 2020, Bari, Italy Cadavid, et al.
Figure 8: Distribution of the selected approaches for System-
level architecture evaluation
Figure 9: Distribution of Software–level architecture evalu-
ation approaches given the followed System-level architec-
ture evaluation approaches
decisions were evaluated only when the system became operational
(i.e. the entire SoS running in a production environment). Second, in
most cases, a combination of two or more system-level evaluation ap-
proaches took place. Further related phenomena can be identied in
Fig. 9, which shows the distribution of the approaches followed for
the evaluation of software-level architectural decisions, given the
approaches followed for the system-level ones. While Evaluation in
Production must include some evaluation of the software, for each
of the other three evaluation approaches there were a portion of
projects that reported doing no evaluation of software architecture
decisions. Furthermore,
in most of the systems that used a for-
mal approach for the validation of their architecture, there
was no separate evaluation at software-architecture level, or
it was considered as implicitly evaluated. (Finding 7)
Regarding the problems arising by combining system-level and
software-level evaluation approaches (Q 3.6), the QCA analysis cat-
egorized the 22 free-text responses in four codes: Architecture
Patching,Insufficient Evaluation,Evaluation Criteria and
Evaluation Complexity. It is interesting that the responses linked
to the most frequent problem category, Architecture Patching,
were not related to the evaluation process per se, but to the eort
required to address the issues found by the evaluation. Some re-
sponses suggest that a major part of the cost of these architecture
patches is due to the lack of clarity about which level (system or
software) to make the changes. Moreover, it is noteworthy that the
architectural evaluation of the systems linked to these responses
was either performed late in the process (in production) or through
throw-away prototypes.
A number of respondents also report Insufficient Evaluation
due to informal evaluation procedures, insucient attention, or lack
of learning from the evaluation. Finally, the categories Evaluation
Complexity and Evaluation Criteria both identify challenges
in performing an evaluation. The rst includes responses that de-
scribe how the complexity of the architectural descriptions and the
processes involved in the system operation makes the evaluation
process equally complex. Evaluation Criteria includes responses
that describe the challenges on their denition given the need for
addressing both system- and software-level elements.
4.4 Questions related to RQ2
The results presented in this section concern the problems posed by
the interplay between SWE and the SE disciplines while addressing
two of the most distinctive characteristics of an SoS [
]: Emergent
Behavior of an SoS and the Independence of its constituents. These
questions were presented only to the respondents who scored these
characteristics higher than 0 for their reference system.
4.4.1 Emergent behavior. Q 4.1 asked respondents whose system
presented some degree of emergence (54 out of 60), whether this
characteristic was an architectural concern, and if so, at which levels
(system or software level, or both) it was addressed. As seen on Table 5,
only 13% of this subset reported that emergence was not an archi-
tecture concern, whereas in most of the cases (43%) emergence was
addressed as an architectural concern at both system and software
level architectures. Only in a small fraction of the cases emergence-
related architectural concerns were addressed exclusively at either
the system or software level (7% and 4% respectively).
In the follow-up question (Q 4.2), respondents were asked an
open-ended question about the problems posed by the way that emer-
gence was addressed. QCA was performed on the responses and
3 codes linked to requirements-related problems emerged as the
most prominent ones. The rst, Modeling and Simulation Limi-
tations, includes quotes on how the limitations of the modeling
approaches for highly complex systems and the imperfectness of the
simulation approaches make it dicult to anticipate and address un-
desired emergent behaviors. The second code, Subsystems-related
Emergence Causes includes quotes that describe problems at the
Constituent System level related to undesired emergent behaviors,
particularly failures and timing problems with low level hardware
components. Together, the quotes linked to these two codes suggest
low level hardware components, despite being one of the
root causes of undesired emergent behavior, are sometimes
not considered in the architecting process of SoS. Further-
more, this could be due to limitations of the modeling and
simulation approaches, where such low-level components
are not considered due to the granularity level of such ap-
proaches. This is particularly important since simulation is
the most common approach to evaluate architectural deci-
sions at system level (Finding 8), as discussed in Section 4.3.3.
Finally, quotes linked to the third code, Time and Resources
Problems, describe both resource-related causes (insuciently allo-
cated time and resources) and consequences of undesired emergent
behavior (added costs, rework eort).
4.4.2 Autonomy/Independence. The interdisciplinary problems be-
tween SE and SWE related to the characteristic of independence of
SoS constituents are explored through questions Q 4.3,Q 4.4 and
A Survey on the Interplay between Soware Engineering and Systems Engineering during SoS Architecting ESEM ’20, October 8–9, 2020, Bari, Italy
Table 5: Frequency of the responses given to Q 4.1: desired
or undesired emergent behavior as an architectural concern,
and means to address it
Response Frequency
Emergent behaviour was addressed by both system-level
and software-level architecture
Emergent behaviour was a concern, but it was not ad-
dressed by the architecture
Emergent behaviour was not a concern 7
Emergent behaviour was addressed only by system-level
Emergent behaviour was addressed only by software-level
Other 8
Q 4.5. These problems are explored from the perspective of the
interfaces and interface specications of the constituent systems.
More specically, Q 4.3 asked the respondents about the existence
of interface specications of the system’s constituents and the de-
tails provided in the specications. All 60 respondents scored the
characteristics of Autonomy or Governance (corresponding to Op-
erational and Managerial independence, respectively) above zero
for their reference systems, and so these questions were presented
to all respondents. However, only 28 respondents provided informa-
tion about the details provided in the interface specications and
only 3 respondents reported cases where all specication elements
(syntactic, behavioral and QoS) were present.
Q 4.4 asked respondents about the kind of problems posed (if
any) at system and software architecture level by the integration of
independent constituents. Out of the 60 respondents, 13 identied
integration problems at software level due to loose or inconsistent
specications. 17 identied problems at system level due to incom-
plete specications; 7 of those responses did not oer any further
clarication, while the remaining 10 responses reported incom-
plete specications, irrespective of what and how many interface
specication types were developed.
In the follow-up question (Q 4.5), respondents were asked an
open-ended question about the problems posed by the changes or evo-
lution of the independent constituents, given the way their interfaces
were provided. QCA was performed on the 24 responses and one
of the most common codes was Incomplete Interface Specifica-
tions. Despite its prominence, Incomplete Interface Specifica-
tions can be seen as a cause of problems as the constituent systems
change or evolve, rather than a problem per se. However, since 50%
of the respondents reported some kind of problems due to incom-
plete or inconsistent interfaces (Q 4.4), the results of the qualitative
analysis on this question suggest that
the unclear/incomplete
interface specication problems faced during the system in-
tegration remain an issue as the independent constituents
evolve. This suggests that unclear/incomplete interface spec-
ication problems could be a cause of technical debt in SoS.
(Finding 9)
Another common code, Conguration Management,
provides further insight into problems that arise as the constituent
systems evolve. These quotes describe how
inadequate congura-
tion management of interface specications and the lack of
policies for their life-cycle lead to specications that were
out-of-sync with reality. Moreover, communication of the
specication changes to the interested parties might not be
considered as part of the conguration management process.
(Finding 10)
The remaining two codes reect issues related to
the management of change: how resources are allocated (Change
Costs) or the way the changes are approached (Hardware–Software
Changes Balance).
This survey collected data about the problems posed by the interplay
between the SE and SWE disciplines during SoS architecting in
practice. Each respondent was asked to characterize their reference
system along 8 dimensions. We discovered that there were only
minor dierences in these characterizations between respondents
that labeled their system as SoS and those that did not. (
Finding 1
This, together with the strikingly low adoption of SoS-specic
guidelines, frameworks and tools for system development even in
systems explicitly identifying as SoS (
Finding 2
), points to a state
of practice that seemingly fails to take advantage of the existing body
of knowledge about SoS and the accruing benets from it. This gap
between research eorts and industrial needs is something that this
and other empirical studies of SoS and SE/SWE interplay, which
are scarce at the moment could and should contribute to address.
Looking at the research questions, RQ1 focused on SoS archi-
tecture analysis, synthesis and evaluation. The results show that
software requirements are in most cases subordinate to system-level
requirements. Although this is not surprising, our study highlighted
major issues in the software part of the system when its require-
ments are derived or based on higher-level system requirements
Finding 3
); consider for example, the cycle of interdisciplinary co-
ordination problems (also reported in other studies e.g., in [
]) and
assumptions made about each other’s discipline leading to missed
requirements. In other cases, misinterpretations of the system-level
requirements are reported, either due to their incompleteness or a
lack of domain knowledge of the software engineers. Problems like
the lack of domain knowledge, or the lack of ‘system-perspective’
have been recognized since the earliest related literature [
However, the fact that software engineers are perceiving the in-
completeness of system-level requirements as a cause of misinter-
pretation urges further research towards requirement specication
approaches that are more balanced for both disciplines.
Considering how architectural design decisions at the system
and software level are taken, we found that in many systems (41%)
such decisions were taken by separate teams working indepen-
dently at each level. Intuitively, this approach is more likely to
be linked to problems in a project, however it turns out that the
distribution of integration and documentation issues—the most
frequent ones overall—are almost identical when compared to the
systems whose design decisions were taken by interdisciplinary
teams working together (
Finding 4
). This suggests that there may
be forces common to both approaches that cause these problems, with
further study warranted to identify the root causes of the problems.
The high percentage of integration problems (above 70%) reported
Finding 5
)further reinforces our previous point about the impor-
tance of bridging the gap between research and industry. For instance,
ESEM ’20, October 8–9, 2020, Bari, Italy Cadavid, et al.
a signicant number of studies on SoS interoperability have already
been reported [
] but barely ever used. Furthermore, more than
50% of systems using either architecture decision approach (inter-
disciplinary vs. separate), report documentation-related problems.
This suggests that even with a closer cooperation between the two
disciplines, the consistency of the architecture documentation is
still problematic. It might therefore be worth developing an archi-
tecture description language or framework for better capturing details
at both levels, while reconciling the terminology dierences.
Turning to the evaluation phase of the architecting process, we
found that system-level architectural decisions are evaluated, in
most cases, through a combination of prototyping and simulation
approaches. However, the architectural decisions at software level,
despite being taken independently in many cases, are almost ex-
clusively validated against system-level requirements (
Finding 6
or even considered as implicitly evaluated, particularly in systems
evaluated using a formal approach (
Finding 7
). This suggests that
in most SoS governed by a systems engineering process, the evalu-
ation process might not be considering the software requirements
(esp. non-functional requirements) when they are not explicitly
linked to a higher-level system requirement. This is worth explor-
ing further through studying the implications of not integrating
software-specic architecture evaluation methods in higher-level sys-
tem evaluation processes, as well as ways to integrate such evaluation
We also explored the interdisciplinary problems linked to the
independence of SoS constituents and the behaviors that emerge
from the constituents’ cooperation [
]. The results of the survey
show very few problems explicitly linked to the interplay of SE and
SWE disciplines when dealing with undesired emergent behavior.
However, the results reveal another issue to investigate further: fail-
ures of low-level hardware subsystems, which are not considered in the
modeling or simulation environments due to their granularity level,
are a common cause of undesired emergent behavior (
Finding 8
Furthermore, it is worth exploring to what extent software subsys-
tems are causing emergent behavior, because (like low-level hardware
subsystems) they might not be included in higher-level system models
and simulations.
Finally, the characteristic of constituent system independence
was explored from the perspective of the interfaces provided for
the integration of the independent constituents. We found that the
problem of incomplete specications is reported both early in the
integration process and during system evolution. This seems to
be a common cause of technical debt in SoS projects (
Finding 9
Interestingly, another problem identied in this study could be the
key to address this kind of technical debt: insucient interface
specications management (
Finding 10
). As suggested by some
of the respondents, interface management in SoS should not only
become mandatory, but it needs to go beyond tracking and con-
trolling documentation changes to consider the full life cycle of
interfaces and the distribution/communication of changes to the
involved parties. An extension to the interface management processes
dened in well-known engineering bodies of knowledge [
], con-
sidering the aforementioned life cycle and distribution elements, and
the hardware-software interfacing problems discussed in previous
works (e.g. [17]), is worth exploring further.
Overall, we feel that software engineering as a discipline, when
applied in the context of larger systems and particularly SoS, must
address the interplay with other disciplines and move towards using
standardized practices. We would like to note in particular that most
of the works that explore the interdisciplinary problems between SE
and SWE, like the ones discussed in Section 2, actually come from
the SE community. For instance, although the Systems Engineering
Body of Knowledge (SEBOK) [
] acknowledges the interdisciplinary
challenges with the software engineering discipline, the Software
Engineering Body of Knowledge (SWEBOK) [
] makes very few
references to other engineering disciplines. The research topics
derived from this study and other similar empirical studies in the
eld could contribute signicantly to this underrepresented aspect
of the software engineering discipline.
The Systems Engineering (SE) and Software Engineering (SWE)
disciplines are highly interdependent in the development of modern
SoS in industries like defense, automotive, energy and health care.
However, the literature suggests that the gaps or inconsistencies
between the architecting approaches followed by each discipline
often cause system-wide problems in the resulting systems. This is,
to the best of our knowledge, the rst empirical study that explores
the problems experienced by practitioners in the architecting pro-
cess of SoS when both disciplines are involved. For this purpose
we designed, piloted and carried out an online questionnaire-based
practitioner survey. We obtained a total of 60 pertinent responses.
The results of this study revealed predominant problems related
to three architecting artifacts that could benet from further in-
terdisciplinary research, namely requirements specications across
system and software level, architectural description languages for the
documentation of the system, and interface specications to enable
the independent evolution of the constituent systems. In addition,
the ndings of this study also show persistent issues with SoS ar-
chitecting resulting in integration diculties and an apparent low
priority given to the evaluation of software-specic architectural
decisions. In combination with the reported very low adoption of
the existing body of knowledge, such issues are a cause of concern
and a call for further interdisciplinary research between SE and
SWE. Last but not least, this study also uncovered a phenomenon
linked to undesired emergent behavior worthy of further explo-
ration: limitations of current system-level modeling and simulation
approaches due to their exclusion of low-level components.
In addition to working on the open research issues identied
in Section 5, in the future we plan to conduct further empirical
studies oriented towards the identication of SE/SWE architecting
harmonization practices in SoS and their relation to the problems
identied in this study.
This work was supported by ITEA3 and RVO under grant agreement No.
17038 VISDOM (
The authors would also like to thank the participants to the pilot studies
of this work for their invaluable help: Rochus Keller, Osasai Macauly, Sally
C. Muscarella, Philippe Krutchen, Lars de Groot, Remco Poelarends and
Sarah Sheard, and the anonymous reviewers for their comments.
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This chapter defines the overall tool-supported “AMADEOS architectural framework”, with its main building blocks and interfaces. It particularly focuses on Structure, Dependability, Security, Emergence, and Multi-criticality viewpoints of an SoS.
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In an effort to explore the relationship between the disciplines of systems engineering and software engineering, professionals from academia, industry, and government gathered for a workshop to deliberate on the current state, to acknowledge areas of inter-dependence, to identify relevant challenges, and to propose recommendations for addressing those challenges with respect to four topical areas: 1) Development Approaches, 2) Technical, 3) People, and 4) Education. This paper presents the deliberations and recommendations that emerged from that workshop, and the proposed project to be launched.
(Elsevier's Share link, available until December 12th, 2019: ) Context: The term System of Systems (SoS) has increasingly been used in a wide variety of domains to describe those systems composed of independent constituent systems that collaborate towards a mission that they could not accomplish on their own. There is a significant volume of research by the software architecture community that aims to overcome the challenges involved in architecting SoS, as evidenced by the number of secondary studies in the field published so far. However, the boundaries of such research do not seem to be well defined, at least partially, due to the emergence of SoS-adjacent areas of interest like the Internet of Things. Objective: This paper aims to investigate the current state of research on SoS architecting by synthesizing the demographic data, assessing the quality and the coverage of architecting activities and software quality attributes by the research, and distilling a concept map that reflects a community-wide understanding of the concept of SoS. Method: We conduct what is, to the best of our understanding, the first tertiary study on SoS architecting. Such tertiary study was based on five research questions, and was performed by following the guidelines of Kitchenham et al. In all, 19 secondary studies were evaluated, which is comparable to other tertiary studies. Results: The study illustrates a state of disconnection in the research community, with research gaps in the coverage of particular phases and quality attributes. Furthermore, a more effective approach in classifying systems as SoS is required, as the means of resolving conceptual and terminological overlaps with the related domains. Conclusions: Despite the amount of research in the area of SoS architecting, more coordinated and systematic targeted efforts are required in order to address the identified issues with the current state of research.
While the phrase “system-of-systems” is commonly seen, there is less agreement on what they are, how they may be distinguished from “conventional” systems, or how their development differs from other systems. This paper proposes a definition, a limited taxonomy, and a basic set of architecting principles to assist in their design. As it turns out, the term system-of-systems is infelicitous for the taxonomic grouping. The grouping might be better termed “collaborative systems.” The paper also discusses the value of recognizing the classification in system design, and some of the problems induced by misclassification. One consequence of the classification is the identification of principal structuring heuristics for system-of-systems. Another is an understanding that, in most cases, the architecture of a system-of-systems is communications. The architecture is nonphysical, it is the set of standards that allow meaningful communication among the components. This is illustrated through existing and proposed systems. © 1999 John Wiley & Sons, Inc. Syst Eng 1: 267–284, 1998
This book presents Systems Engineering from a modern, multidisciplinary engineering approach, providing the understanding that all aspects of systems design, systems, software, test, security, maintenance and the full life-cycle must be factored in to any large-scale system design; up front, not factored in later. It lays out a step-by-step approach to systems-of-systems architectural design, describing in detail the documentation flow throughout the systems engineering design process. It provides a straightforward look and the entire systems engineering process, providing realistic case studies, examples, and design problems that will enable students to gain a firm grasp on the fundamentals of modern systems engineering. Included is a comprehensive design problem that weaves throughout the entire text book, concluding with a complete top-level systems architecture for a real-world design problem.
For a large-scale system of systems (SoS), severe integration and run-time problems can arise due to inconsistencies, ambiguities, and gaps in how quality attributes (such as reliability) are addressed in the underlying systems. This is exacerbated in contexts where major system and software elements of the SoS are developed concurrently and oftentimes independently. Using a defense system scenario, this article outlines a uniform approach for capturing quality attribute requirements as augmentations to mission threads early in the development process and for analyzing SoS, system, and software architectures against these mission thread augmentations.