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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>Z. Liu);</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>SysDO: A Domain-Level Ontology for Cross-Domain System Design in Aircraft Manufacturing</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Zhengyu Liu</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Sina Namaki-Araghi</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Arkopaul Sarkar</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Amine Karoui</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Rebeca Arista</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Mohamed Hedi Karray</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Airbus SAS</institution>
          ,
          <addr-line>31700 Blagnac, Midi-Pyrénées</addr-line>
          ,
          <country country="FR">France</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Université de Technologie Tarbes Occitanie Pyrénées</institution>
          ,
          <addr-line>65000 Tarbes</addr-line>
          ,
          <country country="FR">France</country>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>University of Seville</institution>
          ,
          <addr-line>41092 Seville</addr-line>
          ,
          <country country="ES">Spain</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2025</year>
      </pub-date>
      <volume>000</volume>
      <fpage>0</fpage>
      <lpage>0002</lpage>
      <abstract>
        <p>System design in complex manufacturing industries like aeronautics faces challenges of semantic fragmentation across diferent layers, such as operational, functional, logical, and technical. Existing ontologies lack domainspecific semantics to unify multi-layer interdependencies, leading to interoperability gaps and traceability issues in model-based systems engineering (MBSE). To address this, we propose the System Design Ontology (SysDO), a domain-level ontology extending BFO/IOF-core to formalize cross-layer relationships, ports, functions, and processes. SysDO bridges semantic discontinuities by integrating SysML-aligned hierarchical perspectives (global, factory, hangar, station) and enabling tool-agnostic interoperability. Evaluated through competency questions on an aircraft manufacturing case study, the query results from the knowledge graph under the SysDO schema confirm its utility in retrieving activities, components, and system structures across layers.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Ontology</kwd>
        <kwd>Design model</kwd>
        <kwd>MBSE</kwd>
        <kwd>Manufacturing system design</kwd>
        <kwd>Semantic Web</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        System design serves as the backbone of system engineering—a discipline ubiquitous across domains
like manufacturing, software, and business [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. In complex manufacturing industries specifically, the
integration of multi-level hierarchies and multi-view perspectives directly impacts eficiency and cost.
In aeronautics manufacturing, for instance, fragmented system models lead to semantic discontinuities:
operational requirements fail to propagate coherently to technical implementations, cross-departmental
collaboration is hindered by the lack of interoperability, and traceability of errors and defaults gets
impeded. Current model-based systems engineering (MBSE) approaches, while structured, struggle
with heterogeneous tool silos: SysML models for functional design, CAD tools for physical layouts,
and simulation suites for discrete event simulation. All of them operate in isolation, forcing manual
reconciliations and risking design drift. Even within the system design itself, requirements, functions,
operations, and technical specifications remain insuficiently orchestrated.
      </p>
      <p>Existing ontological solutions for Systems Engineering (SE) have ofered valuable insights, yet
have not fully resolved these gaps. A primary limitation is that they are often case-specific and lack
extensibility to more generalized scenarios. Another frequently witnessed limit is that they tend to
focus on the specific perspectives, such as one from the operational, functional, logical, and technical
views, without adequately integrating the critical relationships and constraints between these views.
These approaches cannot retrieve and represent the totality of information of a complex system design
model, where relationships and constraints among multiple views are critical for understanding system
behavior, cause traceability, and overall architectural integrity.</p>
      <p>In this research, we develop the System Design Ontology (SysDO) in order to overcome these
limitations. SysDO formalizes relationships and interdependencies across Operational, Functional,
Logical, and Technical layers to enable tool-agnostic interoperability. The proposed ontology is a
domain-level ontology, which is an extension of BFO as a top-level ontology and IOF-core as a mid-level
ontology, tested in the frame of the CORAC-DGAC Excelab project1. SysDO includes specifications
of ports, functions, and processes in the system design. It is evaluated by competency questions that
query a representative case of an aircraft manufacturing system design model provided by Airbus.</p>
      <p>
        This work follows LOT4OCES methodology [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], and the structure is as follows: requirements and
competency questions [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] are defined in Section 2, related work is reviewed in Section 3. SysDO’s
classes and properties are presented in Section 4 with a minimum example. It is then evaluated in the
context of aerospace manufacturing in Section 5. Finally, limitations and future work are discussed in
Section 6.
      </p>
    </sec>
    <sec id="sec-2">
      <title>2. Requirements</title>
      <p>
        To address these fragmentation challenges, we derive requirements focused on integrating certain layers
in the MORFLT framework[
        <xref ref-type="bibr" rid="ref4">4</xref>
        ][
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. This research focuses on models’ heterogeneity and aims to improve
their interoperability within aircraft manufacturing systems, following the SysML v1 language2. Such
production systems are characterized by hierarchical organization and structured interactions across
multiple scopes, such as factory level and station levels, as well as diferent perspectives. The ontology
is supposed to support precise semantic representation of entities and relationships in the product and
system design, thereby enhancing model interoperability and supporting eficient system integration
without dependence on any specific tool or language.
      </p>
      <p>The requirements for our ontology development are based on SysML v1 and placed in the MORFLT
framework (Mission – Operational – Requirements – Functional – Logical – Technical). MORFLT is a
structured approach in systems engineering deployed in industry in complex systems such as vehicle
and aircraft manufacturing. However, for the purpose of this research, we explicitly focus on the
Operational, Functional, Logical, and Technical layers (O, F, L, T), omitting Mission and Requirements.
These selected layers are recognized among most existing system design approaches. They represent
distinct yet interconnected viewpoints in system design, from abstract operational needs to concrete
implementation:</p>
      <p>The Operational layer characterizes the system’s intended use and behaviour by analyzing user
needs, actors, activities, and scenarios under real-world constraints (e.g., performance, functionality,
safety).</p>
      <p>The Functional layer defines the functions the system must have to fulfil operational needs.
Functional need descriptions are considered included in this layer.</p>
      <p>The Logical layer structures the established functions into a technology-independent system
architecture of components and interfaces.</p>
      <p>The Technical layer translates the logical architecture into deployable implementations, integrating
technical choices, physical architecture, and constraints to produce the system design.</p>
      <p>The relationships and constraints among these layers are supposed to be interconnected for trade-of,
deduction and co-engineering, while in practice, they are often isolated by information silos. To bridge
these gaps and enable efective integration across these layers, the ontology must explicitly formalize
the interdependencies and traceability between operational, functional, logical, and technical entities
and relationships. This ensures that constraints, design decisions, and system behaviors can be traced
coherently across layers, addressing the fragmentation inherent in siloed development of models from
diferent perspectives. By establishing these cross-layer relationships, the ontology should act as a
unifying framework to support co-engineering, trade-of analysis, and holistic system validation.
1https://skyreal.tech/news/skyreal-integrates-the-excelab-project-of-the-dgac/
2https://www.omg.org/spec/SysML/</p>
      <p>
        We formulated a set of illustrative competency questions (CQs) from Airbus’s trainer aircraft
production line as part of requirement engineering for the ontology [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. A subset of the complete list of
CQs is provided as follows to minimally address information from various aspects of system design, for
example, structural composition, functional decomposition, material flows between components, and
activity sequences:
      </p>
      <p>CQ1: What are the preceding activity and next activity of trimming during sheet press forming?
CQ2: Which hangar has the function manufacturing elementary parts of wings?
CQ3: What are function parts of the elementary metallic part manufacturing system?
CQ4: What type of input and output materials for the subactivities in surface protection small in
the elementary metallic part manufacturing system?</p>
      <p>CQ5: What resources are used for the final assembly system of the wing?
CQ6: What are the subactivities of sheet press forming? What is the duration of each subactivity?
While these CQs require only the retrieval of explicitly asserted design data, their combination—and,
at times, the inference of new facts—is necessary to address higher-level questions that support critical
decision-making. For example, a “make or buy” analysis requires aggregating parts-level cost data,
production sequences, and alternative material-flow scenarios to compute total production cost. These
higher-order questions lie beyond the scope of this paper and are not included in this paper for brevity.
Despite that these CQs are written in phrasings preferred by domain experts (e.g., designers, architects),
SysDO mostly admits SysML-specific terms as parent classes, which can be extended with various
domain-level terms. In section 5, we show how these CQs are reformulated using these domain-level
terms.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Related work</title>
      <p>Ontologies have been widely adopted in diverse domains, including system design, to ensure semantic
consistency and interoperability across heterogeneous models and domains. In this section, similar
works are presented within the scope of system design and SysML. Other related works are also
introduced in this section to support this study.</p>
      <p>
        In the early work before 2015, Wagner et al. formalized the mapping of State Analysis methodology
to SysML in [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ], providing a structured ontology for capturing and verifying system states, enabling
precise architectural constraints and semantics verification. Graves discussed in [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ] integrating SysML
with OWL, ofering a practical approach to representing SysML block diagrams semantically in OWL
to maintain design fidelity and facilitate ontology-based analysis.
      </p>
      <p>
        In the recent decade, a system engineering reference ontology has been developed in [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ],
extending BFO as a top-level ontology. It focuses on establishing the context and objectives of the digital
artifacts being developed in system engineering processes, while integrating their content into a
uniifed and coherent terminology. An ontology-based requirement verification approach is proposed in
[
        <xref ref-type="bibr" rid="ref9">9</xref>
        ], facilitating automated reasoning and verification in the early design stages of complex systems.
This approach addresses design ambiguity and traceability issues, ensuring requirements are clearly
formalized and verifiable through ontology reasoning. Lu et al. developed a scenario-based ontology
within an MBSE tool chain in [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ]. It formalizes simulation implementations and model information for
automated integration and verification purposes, demonstrating significant enhancements in simulation
processes. Wardhana et al. introduced in [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ] an automatic transformation method converting SysML
Requirement Diagrams into OWL ontologies, enhancing semantic clarity and facilitating knowledge
reuse and analysis across system designs. Zheng et al. proposed in [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ] a semantic-driven tradespace
framework integrating requirement management, architecture definition, and manufacturing system
design through an application ontology, validated in aircraft fuselage assembly case studies. There
are other notable works, including [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ], focusing on developing ontologies for system and process
modeling; however, we could not further discuss them due to the page limit.
      </p>
      <p>
        Aside from the previously mentioned domain-level and application-level ontologies, top-level
ontologies like Basic Formal Ontology (BFO) [
        <xref ref-type="bibr" rid="ref14">14</xref>
        ] and mid-level ontologies like Industry Ontology Foundry
(IOF) [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ] ofer relatively high-level interpretation of general entities but lack domain-specific semantics
for system design. Consequently, top-level and mid-level ontologies can provide theoretical foundations
and reference frameworks. Still, domain-specific refinement is needed to capture diverse system design
information fully in the context of manufacturing.
      </p>
      <p>
        Additionally, the Ontology Definition Metamodel (ODM) by OMG [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ] is a standardized framework
facilitating integration between ontology modeling and model-driven architectures (MDA). It aligns
ontology languages such as OWL and RDF with UML-based modeling frameworks, ensuring semantic
clarity and tool interoperability.
      </p>
      <p>
        The previously mentioned work advances the understanding of the semantic consistency and
interoperability in system design, but also reveals certain limits. One of the limits is that they tend to focus on
a single view, e.g., [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ] and [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ] focus on requirements, [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ] focuses on system states. For complex system
design, this incomplete handling of multiple interconnected aspects ( e.g., technical and behavioral)
and inadequate representation of multi-domain or multi-level relationships among them. This issue
has been highlighted within the current era of digital transformation as one of the primary scientific
challenges in developing relevant services to obtain holistic transparency for decision-makers, where
neglecting interoperability among diferent digital models across an organization could lead to failure
in such projects due to the accumulation of digital model silos [17].
      </p>
    </sec>
    <sec id="sec-4">
      <title>4. Ontology Design</title>
      <p>
        We developed the System Design Ontology (SysDO3) to represent the entities and relationships models
from diferent perspectives and bridge semantic gaps across manufacturing system layers. SysDO is
a Domain-Level Ontology (DLO) built upon Basic Formal Ontology (BFO) [
        <xref ref-type="bibr" rid="ref14">14</xref>
        ] as Top-Level
Ontology (TLO) and Industry Ontology Foundry Core (IOF-core) [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ] as Mid-Level Ontology (MLO). The
inheritance relationships among them are shown in Figure 1 and further illustrated below:
• BFO is a widely adopted TLO that provides a set of general and abstract classes, properties, and
rules from a philosophical point of view. It distinguishes Continuants (entities enduring through
time, e.g., physical components) and Occurrents (processual entities, e.g., material flows). BFO
provides most of the superclasses and super-properties in IOF-Core, which are inherited indirectly
in SysDO. Additionally, some BFO classes are directly inherited as a superclass in SysDO, for
example, bfo: function and bfo: site.
• IOF-core extends BFO as MLO to formalize mid-level industrial concepts in multiple domains. It
introduces core classes and properties such as iof-core: planned process, iof-core: informational
content entity, and iof-core: prescribes, which bridge abstract BFO categories to domain-specific
semantics. For instance, IOF-core’s planned process class refines BFO’s process to represent a
protocol-driven process governed by constraints and schedules and prescribed by some
specifications. Flow is defined in SysDO as a subclass of iof-core: planned process, formalizing material or
information transfers in manufacturing workflows.
• We develop SysDO as DLO to further extend the concepts of BFO and IOF-core in system design.
      </p>
      <p>The classes and properties defined in SysDO focus on scenarios including hierarchical system
decomposition, flow constraints, and cross-layer dependencies.</p>
      <p>The classes and properties in SysDO are explained further in detail in the following tables:
informationrelated classes in Table 1, function-related classes in Table 2, process-related classes in Table 3 and
object properties in Table 4.</p>
      <p>In Table 1, we present the SysDO classes that are subclasses of iof-core: informational content entity.
This iof-core: informational content entity is defined as a content or pattern that conveys information
about some entity, independent of how it is physically or digitally expressed. Its existence depends
3available on GitHub https://github.com/PICS-LGP/SysDO-System-Design-Ontology/tree/main
Figure 1: System Design Ontology (SysDO) overview
on physical or digital artifacts (e.g., books, PDF documents), yet its essence is not tied to specific
dependencies or carriers. In SysDO, we defined:
• sysdo:Function specification : An information content entity that prescribes one or a set of
functions to be carried out within a system through the execution of one or multiple processes.
For example, the content of a specification document defines the structural joining functions
required for aeroplane fuselage assembly. We further defined receiving function specification and
sending function specification for ports presented in Table 2.
• sysdo:Flow specification : A plan specification that prescribes transferring materials,
information, or energy between functions or components. For example, a logistics plan detailing the
movement of the fuselage from the stamping area to the assembly line.
• sysdo:Precedence specification : A plan specification that defines the order or dependency
between functions. For example, a work instruction stating that the wing must be installed only
after it has passed all the quality control phases.</p>
      <p>In Table 2, we focus on port and function:
• sysdo:Port: A site within a system that serves as an interaction point for data, command, material,
or energy exchange. The exchange in ports can be either between processes or entities. For
example, a software module with an incoming port for receiving sensor data and an outgoing port
for transmitting control signals to an actuator. sysdo:incoming port and sysdo:outgoing port are
defined as subclasses of sysdo: port with specified sysdo:receiving function and sending function.
• sysdo:Port function and sysdo:system function: These two are subclasses of function. Function
is a BFO class, defined as a realizable disposition that exists due to an entity’s physical make-up,
designed to be activated under specific conditions. bfo:function is further interpreted in IOF-core,
defined as a capability which is the “primary purpose for which the entity was created or evolved”.
In SysDO, sysdo:system function and sysdo:port function are derived to represent the intended
capability of a system and a port, respectively.</p>
      <p>Table 3 focuses on process-related content. SysDO process-related classes are mainly developed
under the IOF-Core class planned process, which is a subclass of the BFO class process. Process is defined
as an occurrent that unfolds over time and involves at least one material entity as a participant during
some moment of its duration. Planned process is a process that follows a specific plan, such as a protocol
or instruction. It is characterized by intentional guidance rather than occurring spontaneously or by
chance. In SysDO, we have:
• sysdo:Flow: A connector representing the transfer of material, information between system
components prescribed by a flow specification . Flows are classified into material flow and
information flow , depending on the medium of the flow. Material flow refers to an existing IOF-Core
class material location change process to avoid redundancy. Control flow is defined as a subclass of
information flow as the control signal is considered a specific type of information.
• sysdo:Source process and sink process: A source process initiates a flow, while a sink process
terminates it. A source process has no incoming flow and serves as the starting point of a sequence,
whereas a sink process receives the final flow, marking the end of the sequence. Depending on
the nature of the flow involved, these processes can be categorized as either information (control)
or material. A control source process triggers the execution of activities, while a control sink process
deactivates them. Similarly, a material source process introduces material into the sequence, and a
material sink process removes it from the sequence. In SysDO, we also defined sibling classes such
as joint, fork, and merge processes. However, they are not discussed here due to the page limit.
sysdo:has logical
subsystem at some time</p>
      <p>As shown in Table 4, we introduce a set of object properties to model structural and behavioral
relations among functions, systems, and processes. Object properties link instances of classes to other
instances, unlike data properties, which link instances to literals (e.g., strings, numbers). In SysDO, we
have:
• sysdo:has function part at some time: relates two functions where one is a functional part that
enables the other. As an example, the function “body joining” has a function part “spot welding”.
• sysdo:has process part at some time: relates two processes where one is a subprocess that
composes the other. As an example, the process “chassis manufacturing” has process part “chassis
fabrication” and “quality control”.
• sysdo:has subsystem at some time: Relates two systems, where one system is a subsystem part
of another. For example, in the human body, the digestive system has a subsystem, the stomach,
and the circulatory system has a subsystem, the heart.
• sysdo:has input state and sysdo:has output state: Associates a process with its entry process
boundary and exit process boundary, respectively. Process boundary is a BFO class; it is defined
as a temporal part of a process and the smallest temporal process part without its own temporal
part. It is often used to mark instantaneous changes.</p>
      <p>In order to better explain how to apply the classes and properties in the SysDO ontology, we present
a minimum example in Figure 2 to show how to instantiate ontology classes and properties. In this
example, there are two processes in a material flow sequence: a material source process (Wing reception
at inspection) and a material sink process (Wing dispatch from inspection). In real-world applications,
other processes are involved between the source process and the sink process (e.g., static strength
tests, fatigue strength tests), with intermediate transformation stages to represent a meaningful quality
control sequence. However, this simplified layout was intentionally chosen to provide a more explicit
demonstration of core ontological relationships.</p>
      <p>• 1. Process system participation
– Each process (Wing reception at inspection, Wing dispatch from inspection) has its
corresponding participant system (instances: Wing reception system, Wing dispatch system).
– Systems implement system functions (e.g., Wing reception), which are realized by their
associated processes. For example, Wing reception realized by Wing reception at inspection.
• 2. Material flow process sequencing
– Wing reception at inspection (source) transmits material to Wing dispatch from inspection
(sink) through process boundaries:
∗ Wing reception Out: Output process boundary of Wing reception at inspection
∗ Wing dispatch In: Input process boundary of Wing dispatch from inspection
– Each boundary involves participant ports (e.g., Wing reception port Out, Wing dispatch
port In), which fulfil specific port functions (e.g., sending function Wing reception send out,
receiving function Wing dispatch receive in) to enable material transfer.</p>
    </sec>
    <sec id="sec-5">
      <title>5. Evaluation</title>
      <p>In this section, we evaluate the developed ontology by answering the Competency Questions (CQ) posed
in Section 2. The evaluation aims to demonstrate the ontology’s expressiveness, practical relevance,
and its capacity to resolve semantic interoperability and traceability across diferent MORFLT layers in
complex aircraft manufacturing systems.</p>
      <p>Specifically, this evaluation is based on a scenario involving an aircraft manufacturing system provided
by Airbus, modelled in Cameo4. The design model is structured into four hierarchical levels—global,
factory, hangar, and station—and analysed through four distinct views: operational, functional, logical
and technical. The focus of these views aligns with the four layers (O, F,L, T) from MORFLT introduced
4https://www.3ds.com/products/catia/no-magic/cameo-systems-modeler
in Section 2. Figure 3 presents the general architecture of the aircraft production design model. Note
that this diagram is simplified for readability. Some branches and instances, for example, those at hangar
level and station level, are omitted in the layout. In each of the four views, there is a corresponding
decomposition, e.g., functional decomposition. The parthood relationships are described by a specific
object property, based on the ontological class the instance belongs to. For example, in the functional
view, an instance is parsed as a “sysdo: system function”, and its corresponding object property linked
to the subfunctions is therefore “sysdo: has function part”. Between diferent views, corresponding
instances are linked as follows (the inverse object properties not shown in Figure 3 for brevity):
Operation - Technical are linked by “bfo: occurs in” or reversely by “bfo: environs”.
Operation - Function are linked by “bfo: realizes” or reversely by “bfo: has realization”.
Function - Logical are linked by “iof-core: has function” or reversely by “iof-core: function of”.</p>
      <p>Logical - Technical are linked by “sysdo: has logical subsystem” or reversely by “sysdo: is logical
subsystem of”.</p>
      <p>The model contains multiple diagrams from diferent views (e.g., decompositions of functions,
sequence flows of operations) and various system levels (e.g., factory, hangar). For example, Figure 4
is a SysML internal block diagram that illustrates the technical view of aircraft manufacturing at the
global level, describing the allocation of manufacturing processes in diferent factories, as an example
of one of the diverse diagrams in the Airbus design model.</p>
      <p>We developed parsers to convert the system design model from Cameo into a knowledge graph
format under the SysDO schema, enabling querying with SPARQL [18]. Note that the transformation
of SysML models into RDF (Abox construction) poses challenges by itself, such as model-to-ontology
alignment, tool-specific serialization, and consistency checks. These challenges go beyond the scope of
this paper and are not discussed here.</p>
      <p>In Table 5, we presented the CQs in Section 2 translated into SPARQL5. Owing to space limitations,
Table 5 only presents a subset of the CQs, specifically those with the shortest SPARQL translations.
The complete queries and corresponding returns are available on GitHub6 as well as the complete set
of SysDO ontology. SPARQL enables retrieval and manipulation by structured access to the RDF file,
which is the SysDO-based knowledge graph in our case. These queries assess the ontology’s capability
to answer questions about activities, sub-activities, and system structures across diferent MORFLT
layers. These queries are sent to the knowledge graphs as input (feasible on multiple software and
environments, for example, GraphDB7 as a graph database) to get output as answers to CQs. The
correctness of the answers is used to evaluate the quality of the ontology. Due to proprietary restrictions
on Airbus data, the full ABox can not be released to the public. However, an anonymized demo version
of the parsed knowledge graph is available in the same GitHub repository.</p>
      <p>Table 6 summarizes expected versus actual query results: In CQ2 (Hangar-level activities), the
retrieval of “Hangar” shows that the SysDO-based query can identify activities with their associated
locations across diverse levels (e.g., factories, hangars). In CQ5 (System resources), the identification of
associated resources in final aircraft assembly, such as “Bufer 1” and “Final wing assembly”, validates
the model’s ability to represent system-resource associations via sysdo:hasLogicalSubSystemAtAllTimes.
In CQ6 (Sub-activities and durations), the extraction of sub-activities like “Trimming” and “Sheet press
5https://www.w3.org/TR/sparql11-query/
6https://github.com/PICS-LGP/SysDO-System-Design-Ontology/tree/main
7https://graphdb.ontotext.com/
forming” along with their durations (e.g., “30min”, “5min”) demonstrates the model’s capability to
handle nested functional processes and corresponding attributes (e.g., temporal).</p>
      <p>To conclude, the ontology successfully provides the expected answers to the competency questions
to demonstrate that semantic traceability is improved by SysDO across system design layers. It can
bridge model silos and support interoperability in SysML-based engineering tools.</p>
    </sec>
    <sec id="sec-6">
      <title>6. Conclusion</title>
      <p>We presented the System Design Ontology (SysDO), a domain-level ontology designed to bridge semantic
fragmentation across operational (O), functional (F), logical (L), and technical (T) layers in complex
manufacturing systems. By extending the Basic Formal Ontology (BFO) and Industrial Ontology
Foundry Core (IOF-core), SysDO formalizes cross-layer relationships, ports, functions, and processes
while aligning with hierarchical perspectives (global, factory, hangar, station) and addressing diferent
perspectives (e.g., operational, technical, functional). Evaluation through competency questions (CQs)
on an aeronautics manufacturing case study confirmed SysDO’s ability to retrieve activities, components,
and system structures across layers, demonstrating its potential to improve semantic traceability and
tool-agnostic interoperability.</p>
      <p>Despite its contributions, SysDO reveals certain limitations. Firstly, it does not cover all the layers of
the MORFLT framework. Currently, the Mission layer and Requirement layer are missing. Thus, the
traceability is partial from high-level requirement analysis to technical implementations at this stage
of SysDO. Secondly, some classes and axioms in SysDO need refinement, while others risk creating
unnecessary redundancies. For example, the classification of processes (fort, joint, merge) remains the
same for material flow and information. Additionally, the real-world deployment of SysDO relies on
parsers (e.g., Cameo-to-RDF parsers) that transform models into RDF files or knowledge graphs under
the SysDO schema. These parsers remain experimental and require further development and testing in
diferent domains.</p>
      <p>
        Future work will focus on refining the SysDO classes and properties. Following LOT4OCES
methodology [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], we will refine process logic by establishing concise axioms to better model sequences,
concurrencies, and dependencies among processes. We also plan to integrate the layers of Mission and
Requirements into SysDO to formalize top-down traceability from business objectives to technical specs,
aligning with MORFLT’s full scope. We are also working on connecting the system design ontology to
the simulation ontology, thereby improving interoperability between static design models and dynamic
simulation models. We look forward to testing SysDO in various scenarios from other fields to enhance
its broader applicability and generic utility.
      </p>
      <sec id="sec-6-1">
        <title>Acknowledgements</title>
        <p>This work is performed within the EXCELAB project, funded by the Civil Aviation Research Council
(CORAC) of the French Civil Aviation Authority (DGAC). The authors express gratitude to Airbus and
other aircraft manufacturer project partners (Dassault Aviation, Daher Aerospace, Airbus Atlantic and
Liebherr Aerospace Toulouse) for their support and contribution.</p>
      </sec>
      <sec id="sec-6-2">
        <title>Disclosure of Interests</title>
        <p>Since September 2024, Mohamed Hedi KARRAY has joined the European Innovation Council and SMEs
Executive Agency. The views expressed in this publication are the authors’ responsibility and do not
necessarily reflect the views of the European Commission nor of the European Innovation Council
and SMEs Executive Agency. The European Commission, the European Innovation Council, and SMEs
Executive Agency are not liable for any consequences stemming from the reuse of this publication.</p>
      </sec>
      <sec id="sec-6-3">
        <title>Declaration on Generative AI</title>
        <p>During the preparation of this work, the author(s) used ChatGPT and Grammarly exclusively to:
Grammar and spelling check, Paraphrase and reword. After using this tool/service, the author(s)
reviewed and edited the content as needed and take(s) full responsibility for the publication’s content.
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[18] J. Pérez, M. Arenas, C. Gutierrez, Semantics and complexity of sparql, ACM Transactions on
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