Linking Digital Twin Design and Ontologies with Model-Driven
Engineering: Application to Railway Infrastructure
Alexis Chartrain
1,2
, Gilles Dessagne
1
, No
¨
el Haddad
1
and David R. C. Hill
2
1
SNCF R
´
ESEAU, Direction G
´
en
´
erale Industrielle & Ing
´
enierie, F-93210 Saint-Denis, France
2
Universit
´
e Clermont – Auvergne, CNRS, Clermont – Auvergne INP, Mines de Saint-
´
Etienne,
LIMOS UMR CNRS 6158, F-63000 Clermont-Ferrand, France
{alexis.chartrain, gilles.dessagne, noel.haddad}@reseau.sncf.fr, david.hill@uca.fr
Keywords:
Digital Twin, Information System, Metamodels, Meta-Object Facility (MOF), Model-Driven Architecture
(MDA), Model-Driven Engineering (MDE), Object-Oriented Approach, Ontologies, Railway System.
Abstract:
In this position paper, we argue that ontologies, combined with Model-Driven Engineering (MDE) approach
and the object-oriented approach, could be leveraged to produce model-driven Digital Twins. This paper
presents our framework for the production of model-driven Digital Twins using the aforementioned approach.
Despite the interest in existing frameworks, this paper offers a new perspective that could help pave the way
towards a future standardized, generic framework and shows insights of application at the French Railway
Infrastructure Manager, SNCF R
´
ESEAU.
1 INTRODUCTION
The concept of “Digital Twin” first emerged in the
early 2000’s and has seen significant growth since
2015, as evidence by the increasing number of an-
nual publications on the topic, particularly from the
period between 2015 and 2017 (Barricelli et al., 2019;
Semeraro et al., 2021). Indeed, Digital Twins (DTs)
are seen as promising tools for monitoring, simulat-
ing, optimizing, and predicting the behaviour of a
real-world system or product, remotely from a virtual
counterpart that mirrors the actual system or prod-
uct. These capabilities are highly valued in cutting-
edge sectors, which is why DTs are gaining traction in
manufacturing (e.g., Industry 4.0, aerospace), health-
care (e.g., hospitals), transportation (shipping, avia-
tion, maritime, railways) (Barricelli et al., 2019; Se-
meraro et al., 2021; De Donato et al., 2023).
However, defining, designing, and developing a
DT is by no means straightforward. One major chal-
lenge is to deal with the numerous definitions stated
for the DT concept, which vary across sectors, appli-
cations, and use-cases. As a result, there is little con-
sensus on a universal definition of this concept within
the community, both in industry and academia (Tao
and Qi, 2019; Adamenko et al., 2020; Zhang et al.,
2021; VanDerHorn and Mahadevan, 2021; De Donato
et al., 2023; Chartrain et al., 2024). Nevertheless,
a clear definition is crucial to determine what needs
to be designed and developed. Furthermore, creat-
ing a DT requires models (Tao and Qi, 2019; Char-
train et al., 2024); however despite the existence of a
few frameworks, standards and methods for design-
ing and producing DTs (Segovia and Garcia-Alfaro,
2022; Haße et al., 2022), even fewer of these ap-
proaches are model-driven (Zhang et al., 2021).
In computer science, ontologies are considered
as specific, often formalized, conceptualizations ac-
counting for a particular view or vision of the world
(e.g., reality, domain of discourse) which are shared
among a group of people (Gruber, 1995; Guarino,
1998; Maedche, 2002; Gruber, 2008). They are pre-
sented as structured corpus of concepts in relation-
ship (i.e., semantic or taxonomic relations), modeled
in a language allowing further seamless exploitation
by computers. They are often represented by knowl-
edge graphs and formalized through languages such
as the Web Ontology Language (OWL), the Resource
Description Framework (RDF), or the Unified Mod-
eling Language (UML). A computer ontology is al-
ways built for a domain, but less frequently for a
set of domains of knowledge. Ontologies offer high-
potential solutions for analyzing domains, systems,
and products by formalizing their inherent concepts
and interrelationships, thereby providing the founda-
tion for related unifying models. DTs of these sys-
tems or products, considered as their digital repre-
sentations (i.e., a specific type of model) conform to
Chartrain, A., Dessagne, G., Haddad, N. and Hill, D.
Linking Digital Twin Design and Ontologies with Model-Driven Engineering: Application to Railway Infrastructure.
DOI: 10.5220/0013090200003838
Paper published under CC license (CC BY-NC-ND 4.0)
In Proceedings of the 16th International Joint Conference on Knowledge Discovery, Knowledge Engineering and Knowledge Management (IC3K 2024) - Volume 2: KEOD, pages 265-276
ISBN: 978-989-758-716-0; ISSN: 2184-3228
Proceedings Copyright © 2024 by SCITEPRESS Science and Technology Publications, Lda.
265
their related meta-models, following B
´
ezivin’s works
on Model-Driven Engineering (B
´
ezivin and Gerb
´
e,
2001; B
´
ezivin, 2004; B
´
ezivin, 2005).
In this paper, we argue that ontologies com-
bined with Model-Driven Engineering (MDE) stan-
dards and techniques, and the object-oriented ap-
proach could be leveraged to produce model-driven
DTs. This paper aims at presenting our proposal of
framework for the production of model-driven DTs
with the previously mentioned approach. Our goal is
not to dismiss existing frameworks, but to offer a new
perspective that could help pave the way toward a fu-
ture standardized, generic framework.
In section 2, we present an overview of DTs and
ontologies as part of the state of the art. We also pre-
cise the questions addressed in this paper regarding
the production of DTs. Then, in section 3, we intro-
duce our framework which aimed at facilitating the
production of DTs. This framework includes defini-
tions of the key concepts, basic object-oriented prin-
ciples, Model-Driven Engineering (MDE) standards,
ontologies, and the strong links between these ele-
ments. We also discuss the application of this frame-
work at SNCF R
´
ESEAU, the French Railway Infras-
tructure Manager, within the context of producing a
railway system DT as part of the company Informa-
tion System. We give a very concrete example of ap-
plication in railways dealing with turnouts and associ-
ated measurements, especially from the perspective of
monitoring point machines current consumption with
our DT. Finally, we conclude this paper in section 4.
2 DIGITAL TWIN AND
ONTOLOGIES: AN OVERVIEW
In this section, we present a brief state of the art re-
garding the two main topics of our paper: on the one
hand the concept of DT and, on the other hand on-
tologies in computer science. For both of these top-
ics, we proceed to a short overview of their historical
background and a review of existing definitions in the
literature including their main characteristics.
2.1 Where Does the Concept of Digital
Twin Comes From?
2.1.1 Historical Background and Definitions
The scientific community acknowledges Michael
Grieves as one of the first if not the first – author that
introduced the concept of “Digital Twin” in the liter-
ature (Kritzinger et al., 2018; Barricelli et al., 2019;
Madni et al., 2019; Semeraro et al., 2021; Segovia and
Garcia-Alfaro, 2022). Roots of this concept were in-
troduced in 2002 by Grieves, in his presentation slide
show for the formation of a Product Lifecycle Man-
agement (PLM) center, and more precisely in the well
known slide “Conceptual Ideal for PLM” (Grieves
and Vickers, 2017; Barricelli et al., 2019). Although
the concept was not yet designated as “Digital Twin”
at that time, all the elements of Grieves’ definition
were already stated (i.e., a real space, a virtual space,
and a data flow that connects the two spaces together)
(Grieves and Vickers, 2017). These elements, referred
as “Mirrored Spaces Model”, were then presented in
Grieves’ courses on PLM at the University of Michi-
gan in 2003. Grieves himself attributes to John Vick-
ers the origin of the term “Digital Twin”. Accord-
ing to the former, the latter has first proposed it in
the framework of their joint research works. The au-
thors have refined their concepts over the years from
“Conceptual Ideal for PLM” to “Digital Twin”, by
the way of “Mirrored Spaces Model” and “Informa-
tion Mirroring Model”. However, the essence of these
concepts remained mostly the same with the follow-
ing three main aspects: (1) a real space containing
physical products, (2) a virtual space containing vir-
tual products, and (3) a connection between the two
spaces, tying them together through an information
exchange achieved by a data flow (Grieves, 2015;
Grieves and Vickers, 2017).
In 2012, ten years after Grieves’ preliminary
works on the DT concept, NASA proposed their def-
inition in regards of their own needs: A Digital Twin
is an integrated multiphysics, multiscale, probabilis-
tic simulation of an as-built vehicle or system that
uses the best available physical models, sensor up-
dates, fleet history, etc., to mirror the life of its corre-
sponding flying twin. (Glaessgen and Stargel, 2012;
Barricelli et al., 2019).
In 2018, Kritzinger et al. refined the definition
of the DT concept with a proposal for a categoriza-
tion of the different integration levels of a physical
system with a corresponding virtual system (i.e., the
twin). According to the latter, three levels could be
distinguished, respectively named digital model, dig-
ital shadow, and digital twin (Kritzinger et al., 2018).
We detail each one of them thereafter.
A digital model is a digital representation of an ex-
isting or planned physical system without any au-
tomated information flow between the physical
system and its corresponding representation. In
this case, digital data regarding the physical sys-
tem could only be set manually in the virtual sys-
tem; consequently a change of state in one of the
system has no effect on the other.
DTO 2024 - Special Session on Ontologies for Digital Twin
266
A digital shadow is a virtual system (or digital
model) being automatically updated with a data
flow containing information about the physical
system (e.g., gathered with sensors) allowing a
possible control – in the monitoring sense – of the
physical system through the corresponding virtual
system.
A digital twin is a virtual system being both capable
of commanding (i.e., transmission of instructions)
and controlling (i.e., monitoring of up-to-date sta-
tuses such as in the digital shadow case) a physical
system.
To sum up Kritzinger’s position: a digital model is
a digital representation disconnected from any phys-
ical system; a digital shadow imply a one-way infor-
mation flow from a physical system to a correspond-
ing digital representation. Finally only the digital
twin runs a double-way information flow between a
physical system and a corresponding digital represen-
tation (Kritzinger et al., 2018; Segovia and Garcia-
Alfaro, 2022). In addition, (Aheleroff et al., 2021)
based their reasoning on the categorization proposed
in (Kritzinger et al., 2018), but add one more kind:
the digital twin predictive that uses the digital repre-
sentation to process data and perform simulations or
machine learning applications to make predictions.
Following from this position, (Wright and David-
son, 2020), defended in 2020 a clear distinction be-
tween the two notions of “model” and “Digital Twin”.
They argued that the existence of a physical system is
an indispensable condition for a related digital repre-
sentation to be designated by the term “Digital Twin”.
Otherwise, without any physical counterpart, the digi-
tal representation is simply designated as a “plain dig-
ital model”. However, this point of view should be
put in perspective with the PLM vision proposed by
(Grieves and Vickers, 2017) with different types of
DTs (e.g., Digital Twin Prototype, Digital Twin In-
stance) and the approach with further propose, both
embracing the whole lifecycle of the system within
the DT.
2.1.2 Characteristics and Functionalities
According to our previous analysis stated in (Char-
train et al., 2024), we propose to arrange the most
common characteristics and functionalities of DTs
described in the existing literature within the three fol-
lowing aspects:
1. A digital representation of a precise, designated,
system or product often assumed as physical
that interest a group of stakeholders, aiming at
digitally represent this system/product, possibly
in an up-to-date or pseudo real-time manner (Bar-
ricelli et al., 2019; Madni et al., 2019).
2. An information flow between an actual sys-
tem/product and a corresponding digital represen-
tation aiming at controlling (i.e., monitoring) and
eventually commanding the actual system from
its associated virtual counterpart (Grieves, 2015;
Kritzinger et al., 2018; Tao and Qi, 2019; Segovia
and Garcia-Alfaro, 2022).
3. Simulations, predictions, and decisions achieved
based on the current available knowledge of the
actual system (e.g., digital models, data) aim-
ing at anticipate the behaviour of this actual sys-
tem/product by predicting its future likely sta-
tuses as effectively as possible. This is per-
formed thanks to statistics, simulations, optimiza-
tions, and even artificial intelligence tools, based
on the digital representation of the actual sys-
tem/product (Barricelli et al., 2019; Segovia and
Garcia-Alfaro, 2022).
In this paper, we argue that the integration of the ac-
tual system within the corresponding DT and the pre-
dictions achieved thanks to the latter about the former,
both rely on the digital representation containing all
the necessary information to describe, manage, mon-
itor, control, and predict the behaviour of this actual
system of interest throughout its whole lifecycle. As a
result, the digital representation is the cornerstone of
the DT and will constitute our main focus from now
on.
2.2 Ontology or Ontologies?
2.2.1 Historical Background and Definitions
The term “Ontology” is a combination of the Ancient
Greek words ontos and logos, the former meaning
“being” or “what is”, and the latter meaning “treatise”
or “discourse”. Ontology is a branch of philosophy
that originates from Aristotle’s metaphysics, a disci-
pline interested in the study of the being considering
its intrinsic nature, characteristics, and organization;
broadly, the study of existence and reality focusing
on “what exists” (Maedche, 2002; Gruber, 2008).
We consider that the field of Ontology allows
practitioners of the discipline (e.g., philosophers) to
produce ontologies. Guarino, then Maedche high-
lighted the paramount importance of differentiating
the Ontology (i.e., the philosophical discipline) from
an ontology or ontologies in its plural form that
designate “a particular system of categories account-
ing for a certain vision of the world” (Guarino, 1998;
Maedche, 2002). As for Gruber, he thinks an ontol-
Linking Digital Twin Design and Ontologies with Model-Driven Engineering: Application to Railway Infrastructure
267
ogy in philosophy in a similar manner, that is as “a
systematic account of Existence” (Gruber, 1995).
Furthermore, nowadays ontologies are not only
contained to the field of philosophy anymore; it has
indeed considerably expanded to the field of com-
puter science over the past three to four decades.
We have recently seen various applications in Artifi-
cial Intelligence (e.g., machine learning, deep learn-
ing, Large Language Models), Computational Lin-
guistics, Knowledge Engineering (e.g., knowledge
representation, data/information modeling, object-
oriented analysis, shared digital libraries of reusable
concepts/knowledge components, Information Sys-
tems) and Database Theory (e.g., heterogeneous data
management, multi-database systems interoperabil-
ity) (Guarino, 1998; Gruber, 1995; Gruber, 2008).
Like philosophers, computer scientists are also pro-
ducing ontologies to organize and formalize their
knowledge, for example to better understand a do-
main. Computer scientists first and foremost use them
to make high-level languages computable. In addi-
tion, Knowledge Engineering and Database Theory
are promising fields that should be considered for the
design and the production of DTs, especially in the
framework of Information Systems. In the light of the
above, the need of better approaching the concept of
an ontology with a focus on computer science clearly
appears; therefore we establish a corpus of definitions
of an ontology in computer science in the next section.
2.2.2 The Concept of Ontology in Computer
Science
Probably one of the most famous definitions of an
ontology in computer science, is the following one
stated by Gruber: an ontology is an explicit speci-
fication of a conceptualization (Gruber, 1995; Gru-
ber, 2008). The so-called “conceptualization” is an
abstract, simplified view of the world that we wish to
represent for some purpose or an abstract, simpli-
fied view of a domain of discourse (Gruber, 1995;
Gruber, 2008; Aßmann et al., 2006; Valiente et al.,
2011). According to Guarino, then Maedche: an on-
tology refers to an engineering artifact, constituted by
a specific vocabulary used to describe a certain real-
ity, plus a set of explicit assumptions regarding the in-
tended meaning of the vocabulary words (Guarino,
1998; Maedche, 2002). As for Ben Sta et al., they
define an ontology as an explicit and formal shared
abstract view of a part of the real world. This view
is described by a whole [set] of tools as a vocabulary
formed of concepts, relations, axioms and rules of in-
ference” (Ben Sta et al., 2005).
The nature and the characteristics of an ontology
in computer science are for the most part, acknowl-
edged in the literature: it is a conceptualization with
shared, explicit, and possibly formal aspects. The dif-
ferent kinds of components of ontologies are: con-
cepts, relations, and axioms (Gruber, 1995; Ben Sta
et al., 2005; Aßmann et al., 2006; Gruber, 2008; Va-
liente et al., 2011).
Furthermore, ontologies are classified in several
levels depending on their scopes. According to (Guar-
ino, 1998) then (Maedche, 2002), there are: (1) top-
level ontologies, also known as upper-level ontolo-
gies, which describe common high-level concepts of
a general vocabulary (e.g., space, time, matter, object,
event, action) independent from any domain, task, or
problem; (2) domain ontologies and tasks ontologies,
which describe concepts related to the vocabulary of
a specific domain (e.g., railways) or a given task, by
specializing concepts from a top-level ontology; and
(3) application ontologies, linking domain and task
ontologies by describing the roles played by domain
entities through the performance of a given process,
activity, or task.
2.3 Still Problems
As stated in the introduction of this paper and already
highlighted in one of our previous publication, there
are still remaining open questions about DTs (Char-
train et al., 2024). First, it appears that hardly any
clear consensus on a generic, universal, definition of
the concept of Digital Twin exist to date among re-
searchers and practitioners in the community (Tao and
Qi, 2019; Barricelli et al., 2019; Adamenko et al.,
2020; Zhang et al., 2021; VanDerHorn and Mahade-
van, 2021; De Donato et al., 2023). To illustrate this
problem, let’s take the following example: among the
75 papers reviewed in (Barricelli et al., 2019), only 31
provided a definition of the DT concept, counting 29
different definitions in total. Depending on the defi-
nitions provided in the papers, these papers were then
categorized in the 6 following topics: (1) Integrated
system (2) Clone, counterpart (3) Ties, links
(4) Description, construct, information (5) Simu-
lation, test, prediction (6) Virtual, mirror, replica
(Barricelli et al., 2019). In addition, based on a cor-
pus of 150 papers and an analysis of 30 definitions of
the DT concept, (Semeraro et al., 2021) proposed a
classification of these definitions following five clus-
ters: (1) Lifecycle”, (2) Cyber-Physical Systems”,
(3) “Real and virtual spaces in loop”, (4) “Behaviour
modeling of a physical space”, (5) Virtual system
i.e., replication of a physical system. In (Chartrain
et al., 2024), we conjectured that numerous defini-
tions of the DT concept might exist because it is fore-
most approached with use-cases (e.g., lifecycle man-
DTO 2024 - Special Session on Ontologies for Digital Twin
268
agement, control/command, predictive maintenance)
and not by defining its very nature; according to Bar-
ricelli et al.: literature works have never described
in detail the characteristics of a generic DT. Indeed,
each state-of-the-art paper concentrates on the devel-
opment of few components of DTs (Barricelli et al.,
2019). In the next section, we will propose a generic
definition that we hope broad enough to embrace as
many cases as possible, and as reusable as possible.
We will then refine this definition to suit our objective
regarding the production of DTs with our framework.
Secondly, it appears as well that any DT requires
models to be produced (Tao and Qi, 2019; Tao et al.,
2022). In (Chartrain et al., 2024), we quoted Tao
and Qi: To build a digital twin of an object or sys-
tem, researchers must model its parts (Tao and Qi,
2019). We also underlined the importance of concep-
tual models (i.e., ontologies) since they contain all the
necessary semantics (i.e., concepts and relationships)
to create digital representations of systems accurately
from the desired point of view in DTs. Pieces of
information within digital representations are stored
through data, according to the structure of concepts
in related conceptual models.
A few frameworks and methods currently exist to
produce DTs: we could for instance cite the DT Ar-
chitecture Reference Model (Aheleroff et al., 2021),
the design principles for shared DTs in distributed
systems (Haße et al., 2022), the proposal for design,
modeling, and implementation (Segovia and Garcia-
Alfaro, 2022). Also, ISO standards were recently
published: ISO 23247:2021 focused on automation
& manufacturing, then ISO/IEC 30173:2023 with a
larger scope. However, these frameworks, methods,
and norms are only on early stages of maturation;
therefore there is hardly any consensus among the
community about which ones should be used in each
case in order to design and produce a DT (Tao and
Qi, 2019; Zhang et al., 2021; De Donato et al., 2023;
Segovia and Garcia-Alfaro, 2022). Regarding model-
driven DTs, only Zhang et al. describes a model-
based approach using MDE techniques to design a DT
considering its whole lifecycle (Zhang et al., 2021).
However, the latter doesn’t focus much on model-
ing choices i.e., what should be represented and how.
Based on requirements, the production of models con-
stitutes just a step in the whole framework proposed
to design a complete DT in (Zhang et al., 2021). Our
framework presented in the next section is our contri-
bution to mitigate this lack and initiate a bridge be-
tween DT designing and ontology engineering.
3 LINKING DIGITAL TWIN
DESIGN AND ONTOLOGIES
WITH MODEL-DRIVEN
ENGINEERING
In this section, we present our proposal of metamod-
eling framework regarding the design and the produc-
tion of a Digital Twin as part of an Information Sys-
tem, using ontologies, the object-oriented approach,
and existing standards coming from Model-Driven
Engineering (MDE). We first introduce the object-
oriented approach and the standards we are using,
secondly we propose our definitions of the key con-
cepts given this context and, thirdly we present our
complete proposal. Finally, we provide an example
of application at SNCF R
´
ESEAU, the French Railway
Infrastructure Manager.
3.1 World Modeling Approaches
3.1.1 Object-Oriented Approach
The object-oriented approach relies on the concepts
of instances and classes (Dahl and Nygaard, 1966).
The instance is constituted of a finite set of attributes
and a finite set of methods; each attribute is defined
by its name (i.e., a property name) and its associated
value; similarly, each method is defined by its name
(i.e., a function name) and its returned value.
In Object-Oriented Programming (OOP), an in-
stance is generated from a class that is, a common
structure containing generic attributes and methods
for instances. For that matter, a class could be consid-
ered as a model for instances: A class forms a model
for the creation of instances which are only individual
representations of this model. (Hill, 1996). Also, we
could draw a strong link between a class and a concept
in an ontology, considering their close definitions and
features. The concepts and relationships expressed in
computer science ontologies matches perfectly what
we need to represent through models, and more par-
ticularly when going to an upper modeling level, fur-
ther introduced with the concept of metamodel.
In the DT engineering perspective of our pro-
posal, our goal is to instantiate the digital represen-
tation from classes and to design the classes in ac-
cordance with the concepts inherent to the actual sys-
tem/product with an ontological approach. To do so,
we use existing Model-Driven Engineering (MDE)
standards provided by the Object Management Group
(OMG), further discussed thereafter.
Linking Digital Twin Design and Ontologies with Model-Driven Engineering: Application to Railway Infrastructure
269
3.1.2 Object Management Group Model-Driven
Standards
Our framework requires the use of two OMG stan-
dards: the Meta-Object Facility (MOF) on the top of
the metamodeling architecture and the Model-Driven
Architecture (MDA). It also requires the famous four-
layer metamodeling architecture, commonly illus-
trated with the “meta-pyramid”.
This metamodeling architecture contains four lev-
els respectively called M0, M1, M2, and M3 (B
´
ezivin
and Gerb
´
e, 2001). M0 is the ground level in which no
models are involved (i.e., 0 model = M0), it simply
designates the “real world” in which real systems or
products are contained. M1 is the first level of mod-
eling, embracing models of the real world. M2 is the
second level of modeling, concerned with metamod-
els as models of languages to produce models. Fi-
nally, M3 is the last level of modeling which contains
the unique metametamodel able to describe itself. It
is the MOF within the OMG standard (B
´
ezivin and
Gerb
´
e, 2001; B
´
ezivin, 2005). The M3 layer allows all
metamodels in M2 to be compatible with each other.
In our framework, we stick to B
´
ezivin’s 3+1 revis-
ited organization in which models in M1 represent a
real system in M0, models in M1 conform to meta-
models in M2, and lastly metamodels in M2 conform
to the MOF in M3, the MOF being self-conformant
(B
´
ezivin, 2005). This reflexivity is known as metacir-
cularity by specialists.
The MDA is a standard enabling the object-
oriented analysis, design, and programming in soft-
ware development, allowing an uncoupling of the re-
sults of these activities in three different kinds of mod-
els: (1) Computation Independent Models (CIM) that
are requirement models presenting an analysis of a
domain or a real-world system, through the formal-
ization of related concepts which could be drawn with
an ontology; (2) Platform Independent Models (PIM)
stating software design choices and solutions based
on the analysis in the CIM; and (3) Platform Spe-
cific Models (PSM) constituting object-oriented im-
plementation of the former models. We position all
these models at level M1 in the metamodeling archi-
tecture, this view is shared (Aßmann et al., 2006; Va-
liente et al., 2011). During the whole development
process, we consider that a CIM is transformed in one
or several PIMs, and that each PIM is transformed in
one or several PSMs, depending on the project needs.
This transformation relationship between models is
well documented in Favre’s works on MDE (Favre
and Nguyen, 2005).
3.2 Our Definitions of the Key Concepts
3.2.1 Digital Twin
To define what we have to design and produce, we
first start by defining the DT concept in a broad sense
that is, as an up-to-date digital representation of a sys-
tem of interest. This representation is shared among a
group of people (e.g., stakeholders working in collab-
oration). Furthermore, it can embrace all the neces-
sary pieces of information for describing (e.g., func-
tional models), monitoring/controlling, (e.g., statuses,
measures, alerts, warnings), commanding (e.g., or-
ders, instructions), and simulating (e.g., simulation
models, data) the actual system.
We consider that the integration of the physical
system within the corresponding digital representa-
tion depend on our use-cases and therefore may even
change over time. For example, the DT could contain
information about a system not yet produced, conse-
quently without an immediate physical reality e.g.,
Grieves’ Digital Twin Prototype (Grieves and Vick-
ers, 2017). We give another example: a DT could first
be designed to monitor a system, then upgraded later
to perform control/command, and finally augmented
afterwards to perform simulations based on the dig-
ital representation to inform decisions related to the
actual real-world system. The digital representation
should be capable of addressing all use-cases related
to every phase of the actual system lifecycle during
which we aim to work with the DT.
Hence, we argue that the heart of a DT lies in the
digital representation in the first place. As a result, we
propose to define a DT as follows:
Definition 1. Generic definition. A Digital Twin (DT)
is a shared up-to-date digital representation of a sys-
tem of interest (Chartrain et al., 2024).
Considering now an implementation perspective,
and using the object-oriented approach we have pre-
viously introduced:
Definition 2. Object-oriented technical definition. A
Digital Twin (i.e., as defined in 1) could be imple-
mented with a set of instances generated from a global
and systemic class model. This representation could
be stored in repositories and be accessible through
services (Chartrain et al., 2024).
Of course, this second definition is less generic
and may certainly not be reusable in every case;
it assumes that the design of the considered DT is
achieved with the object-oriented approach. When
using a model-driven approach, choices of other tech-
nical spaces are possible.
DTO 2024 - Special Session on Ontologies for Digital Twin
270
3.2.2 Concepts of (Meta-)Model, Megamodel,
and Ontology
To clearly grasp our framework, it is useful to pre-
cise definitions of the concepts of model, metamodel,
megamodel and ontology to remove any ambiguity.
We fit the definitions provided by Minsky and
B
´
ezivin for the concept of “model”. According to
the former author: To an observer B, an object A
is a model of an object A to the extent that B can
use A
to answer questions that interest him about A
(Minsky, 1965). As for Hill, B
´
ezivin and Gerb
´
e: a
model is a simplification of a system built with an in-
tended goal in mind. The model should be able to an-
swer questions in place of the actual system. (Hill,
1996; B
´
ezivin and Gerb
´
e, 2001). Moreover, a func-
tion of representation mapping models in M1 with
the actual systems they represent in M0 is defined in
(B
´
ezivin and Gerb
´
e, 2001; B
´
ezivin, 2005), then re-
fined in (Favre and Nguyen, 2005; Favre, 2006). This
function, often written µ and read “represents”, is
the essence of modeling; it is used from M1 to M0.
These definitions are sufficient regarding the scope of
this paper.
We rely on Favre’s contributions regarding the
definition of the concept of “metamodel”. Accord-
ing to the latter, a metamodel is a model of language
(i.e., a grammar) through which downer-level models
could be expressed. To be more specific, a metamodel
could either be defined as a model of a language of
models” or a model of a modeling language” (Favre
and Nguyen, 2005; Favre, 2006). B
´
ezivin and Favre
et al. both define a function of conformance, written
χ and read “conformsTo” or “conformantTo”. This
conformance relationship is used to link models to
metamodels from levels M1 to M2, metamodels to
the MOF from levels M2 to M3, and the MOF to it-
self at level M3 thanks to metacircularity (B
´
ezivin,
2005; Favre and Nguyen, 2005; Favre, 2006). The
conformance relationship maps a model with the cor-
responding grammar through which the model is ex-
pressed (Favre and Nguyen, 2005). Furthermore,
B
´
ezivin draw a parallel between the concept of meta-
model and the notion of ontology (B
´
ezivin, 2005).
Our framework requires the concept of “meg-
amodel”, first introduced by B
´
ezivin to define a
model which elements represent models, metamodels
and other global entities” according to (Favre, 2006).
We make use of this concept to express the major
relationships (i.e., representation, conformance, and
transformation) between systems, DT, models, meta-
models, and the MOF within the four metamodeling
layers. In addition, models could be transformed into
other models within these layers thanks to a common
metamodel; for that matter (Favre, 2006) introduced a
function of transformation, written τ and read “trans-
formedIn”.
Based on (Gruber, 1995; Guarino, 1998; Maed-
che, 2002; Gruber, 2008), we consider an ontology in
the computer science meaning. This supposed that, an
ontology is a set of concepts and axioms in relation-
ship with each other through semantic and taxonomic
relations. It represents a specific view of the world
(e.g., reality, particular domain) shared among a com-
munity. Concepts and relations in an ontology are ex-
plicitly expressed through a more or less formalized
language (e.g., OWL, UML) and axioms could be ex-
pressed with a mathematical or first-order logic for-
malism.
3.3 Our Generic Proposal
3.3.1 Synoptic Megamodel
We illustrate our proposal of framework for produc-
ing a DT with MDE through our synoptic megamodel
presented in Figure 1.
In our megamodel, the DT is a digital system at
level M1 that represents (i.e., µ) the actual real-
world system at level M0. Stakeholders can inter-
act with the actual system through its virtual coun-
terpart (e.g., system management, monitoring, con-
trol/command). The virtual system can also ad-
dress other use-cases regarding the actual system,
such as predictions through statistics or simulations.
The digital representation is constituted of a set of
digital objects, instanceOf a digital library of ob-
jects (i.e., concepts describing the actual system). A
chosen object-oriented PSM is embedded in this li-
brary. The digital representation and the digital li-
brary from which it is instantiated are both contained
at level M1. As stated in (B
´
ezivin, 2005), there is a
programming conformance relationship between in-
stances and classes. The same apply here between the
digital representation and the digital library, however
it is not explicitly shown in the diagrams since only
metamodeling conformance relationships are drawn.
This library programmed in a given PSM is the
last product of chain of transformations following the
MDA: first a CIM is defined to formalize all the nec-
essary concepts and relationships related to the real-
world system. The production of the CIM is compa-
rable to the establishment of a domain ontology. This
CIM is then transformedIn (i.e., τ) into one or sev-
eral PIMs in order to satisfy development constraints
and choices. Each PIM is a software solution that is
then transformedIn into one or several PSMs that
are implementation models. CIM, PIMs, and PSMs
are all contained at level M1.
Linking Digital Twin Design and Ontologies with Model-Driven Engineering: Application to Railway Infrastructure
271
M3
M2
M1
M0
MOF
Modeling Language
Metamodel
Object-Oriented Programming
Language Metamodel
CIM
(Domain Model)
PIM
(Design Model)
PSM +
Library of objects
Digital Twin
System of interst
(Actual real-world system)
χ: conformsTo
χ: conformsTo χ: conformsTo
χ: conformsTo χ: conformsTo
χ: conformsTo
instanceOf
µ: represents
τ: transformedIn τ: transformedIn
(generation)
Figure 1: Synoptic megamodel of our framework for producing a DT with MDA and the MOF.
The CIM and the PIMs conformsTo the meta-
model of the modeling languages they are expressed
with (e.g., OWL, UML). CIM and PIMs could be
expressed with the same or different modeling lan-
guages. The digital library of objects conformsTo the
metamodel of the object-oriented programming lan-
guage it is coded with. All these metamodels are con-
tained at level M2 and each of them conformsTo the
MOF at level M3.
3.3.2 Leveraging Ontologies to Formalize
Models
Following from the above, it clearly appears that the
very starting point of the production of the real-world
system digital representation, cornerstone of the DT,
is its corresponding domain model. The latter is ex-
pressed through as CIM using the MDA, as mentioned
previously. Then, one more question remains: how
could we produce this domain model? Since the do-
main is a formalization of a set of concepts in rela-
tionship describing the real-world, and more specif-
ically the scope concerned with the aforementioned
real-world system, it could be established such as an
ontology. This ontology would be a domain ontology,
according to Guarino’s well known classification of
ontologies (Guarino, 1998; Maedche, 2002).
Furthermore, this domain ontology will require
to commit from an upper-level ontology (i.e., also
known as top-level ontology) to reuse, refine, and
specialize really high-level concepts (Guarino, 1998;
Maedche, 2002). Several upper-level ontologies ex-
ist to date, one of the most popular is the Unified
Foundation Ontology (UFO) (Guizzardi, 2005). Oth-
ers could be mentioned such as Basic Formal Ontol-
ogy (BFO), Cyc, Descriptive Ontology for Linguistic
and Cognitive Engineering (DOLCE), General For-
mal Ontology (GFO), PROTo ONtology (PROTON),
Sowa’s Ontology, and Suggested Upper Merged On-
tology (SUMO). All these seven upper-level ontolo-
gies are compared in (Mascardi et al., 2007). We con-
jecture that the choice or the production of a top-level
ontology depends on ontological and epistemologi-
cal assumptions about what is reality and how do we
know what we know, including our knowledge about
reality. However, the scope of this paper is not to ad-
dress this question, but rather to open the discussion
on this subject.
3.4 Application at SNCF R
´
ESEAU
3.4.1 Applied Synoptic Megamodel
We present in Figure 2 the application of our proposal
of framework for producing a DT with MDE, previ-
ously presented in a generic way in Figure 1.
In our company, the actual system we aim at twin-
ing is the railway system. The Digital Twin, seen in
our framework as a shared up-to-date digital repre-
sentation of the railway system among the stakehold-
ers working at and with the company, embraces:
Functional aspect of the infrastructure (e.g., re-
quirements, description of the French Railway
Network within schematics and/or Building Infor-
mation Modeling (BIM) mock-ups) considering
its complete lifecycle i.e., the as-designed phase
embracing the history of all the different versions
of each design study, the as-built phase consid-
ering the actual construction of the infrastructure
and the possible gaps with the as-designed re-
quirements, and finally the as-is phase focusing
DTO 2024 - Special Session on Ontologies for Digital Twin
272
M3
M2
M1
M0
MOF
UML Metamodel Java Metamodel
CIM
(Domain Model)
PIM: ARIANE
(Design Model)
PSM: Java +
Library of railway objects
Digital Twin
Railway system
χ: conformsTo
χ: conformsTo χ: conformsTo
χ: conformsTo χ: conformsTo
χ: conformsTo
instanceOf
µ: represents
τ: transformedIn τ: transformedIn
(generation)
Figure 2: Synoptic megamodel of our framework for producing a DT, applied at SNCF R
´
ESEAU.
on the current configuration of the infrastructure
in which it is operated. This functional aspect in-
clude the description of field elements of the in-
frastructure e.g., tracks, tunnels, bridges, electri-
cal substations, catenaries, signaling items;
Physical aspect of the infrastructure that is, actual
real-world field elements deployed on the French
Railway Network considering their complete life-
cycle i.e., the as-built and the as-is phases. Spe-
cific components of deployed field elements are
supervised for asset management and mainte-
nance purposes e.g., turnout frogs;
Up-to-date measures and statuses related to the
physical infrastructure e.g., sensors controlling
the position of turnout points, sensors monitoring
the current consumption of point machines, sen-
sors ensuring rock-fall, flood, and on-track hotbox
detectors. Each measurement and status is saved
through an history for further analysis;
Railway capacity allocation of the rolling stock
e.g., scheduled train paths, real-time running train
circulations, working zones.
The digital representation is instantiated in reposito-
ries, thanks to our library of objects (i.e., classes de-
scribing railway concepts) in which the Java PSM is
embedded. Java is the main PSM used, since it has
been adopted as a coding standard in our company.
Therefore, the object-oriented programming meta-
model in our framework applied at SNCF R
´
ESEAU is
the Java metamodel. However, other object-oriented
languages could be used as well, such as C++ for sim-
ulation applications. In this case, the digital library
would be written in several object-oriented program-
ming languages, each one conforming to its corre-
sponding metamodel, all metamodels still conforming
to the MOF.
The digital library is produced based on our PIM
named ARIANE” which is a software solution (i.e.,
a design model containing roughly a thousand classes
at the moment) based on the requirements of the CIM
(i.e., a railway domain model). All the concepts re-
lated to the railway system are contained in the CIM,
produced with a global, systemic, and ontological ap-
proach. ARIANE” is a reference PIM for our com-
pany which has been chosen as input, especially its
topology package, for the establishment of the In-
ternational Union of Railways (UIC) standard called
“Rail System Model” (RSM) (Tane et al., 2022; Char-
train et al., 2024). At SNCF R
´
ESEAU, the CIM and
the PIM are both produced in UML, consequently
they both conform to the UML metamodel.
3.4.2 Digital Twin and Information System
At SNCF R
´
ESEAU, our DT is on the one hand, auto-
matically updated by the IoT (e.g., sensors) and, on
the other hand also manually updated by end-users
and data managers (Chartrain et al., 2024). It is our
reference source of information regarding the railway
system, guaranteeing both the unicity and the accu-
racy of data and therefore information (Issa et al.,
2024). As a result, the DT is a major component of
our Information System in the company.
We previously published our DT reference tech-
nical architecture in (Issa et al., 2024). It is achieved
with a Service-Oriented Architecture (SOA) and more
specifically a Representational State Transfer (REST)
Architecture, allowing end-users (e.g., stakeholders
working directly in our company or in partnership
with our company) to access whole or part of the
digital representation contained in the repositories
Linking Digital Twin Design and Ontologies with Model-Driven Engineering: Application to Railway Infrastructure
273
through RESTful web-services (Issa et al., 2024;
Chartrain et al., 2024). Software applications call
web-services and shape the information in the re-
quired format depending on the needs of each end-
user.
3.4.3 Example in Railways: Turnouts and
Measurements
A turnout, also called switch, is a railway field ele-
ment made up of a set of points (i.e., movable ele-
ments of the turnout) and a frog (i.e., central cross-
ing piece of rail within the turnout). Turnouts en-
able the setting of a given direction at a local bifur-
cation within the route of a train. In this example we
are particularly interested in electrically commanded
and controlled turnouts, respectively by the way of
point machines and sensors that check the validity of
the commanded position after the movement of the
points.
The following aspects of turnouts are currently
stored within our DT repositories:
A physical aspect including: (1) each identified
frog of each turnout within the scope of the French
Railway Network and (2) rails, sleepers, and bal-
last related to the track section within which the
turnout is embraced. These latter elements are
only instantiated at the scale of the track section
and not at the scale of the turnout;
A functional aspect including: (1) the network
topology ensured by crossings and turnouts (2) a
precise description of each turnout with especially
its corresponding orientation (e.g., left, right, or
symmetric/Y-shaped), number of branches, num-
ber of points. This description is usually achieved
through track and signaling schematics. The in-
tegration of turnouts models contained in BIM
mock-ups within our DT is foreseen;
Measurements related to the position of the points
and to the current consumption of point machines.
The execution of our framework regarding turnouts
and their related measurements (e.g., points position,
point machines current consumption) requires the es-
tablishment of a domain model for both of these no-
tions i.e., models of “turnout” and “measurement”.
These are components of a CIM, further transformed
into corresponding packages in our PIM that is, AR-
IANE at SNCF R
´
ESEAU. Based on the latter, cor-
responding Java classes related to the concepts of
“turnout” and “measurement” are generated. These
Java classes are then instantiated in our DT reposito-
ries with actual data about the functional and physical
aspects of turnouts, along with related measurements.
Figure 3 shows a simplified domain model re-
lated to a generic concept of “measurement” through
a UML class diagram. It is adapted for the case of
SNCF R
´
ESEAU in order to fit the needs of our com-
pany. However, this model is not complete: it has
been reduced given the informative context provided
in this paper. In our approach, this generic model is
specialized for each context and measured item.
instrumentUsed
1
methodUsed
0..1
contextOfEvent
1
valueUnit
1
valueUncertainty
0..1
0..1
valueRefFrame
measurementAchieved
1
values
1..n
Event
MeasurementEvent
MeasuringInstrument
Method
ContextMeasurement
Value Unit
Uncertainty ReferenceFrame
Figure 3: Simplified generic measurement domain model.
Given that the access to our PIM ARIANE is re-
stricted for intellectual property reasons, we cannot
show a corresponding class diagram extracted from
our PIM. Nevertheless, we provide a link towards
RSM
1
, the UIC standard railway PIM that we have
previously mentioned above. In this latter model, a
model of the concepts of “turnout” and “measure-
ment” can be respectively found in the <<Domain>>
Track and the ObservationAndMeasure packages.
However, ARIANE is still more detailed at the mo-
ment and therefore our PIM related to the concept
of “measurement” is closer to the domain model pre-
sented in Figure 3 than the model presented in RSM.
To complete this example, we provide in Figure
4, an instance diagram (i.e., a UML objects diagram)
that shows how Java classes could be instantiated in
the DT repositories at SNCF R
´
ESEAU. In this ex-
ample, instances are related to the monitoring of a
point machine current consumption, when the points
are maneuvered from one side of the turnout to the
other by the point machines.
4 CONCLUSIONS
The concept of Digital Twin (DT) have first appeared
in the early 2000’s. Since 2015, there has been a sig-
1
https://rsm.uic.org/doc/rsm/rsm-1-2/
DTO 2024 - Special Session on Ontologies for Digital Twin
274
instrumentUsed
1
contextOfEvent
1
PMinvolved
1
turnout
1
valueUnit
1
measurementAchieved
1
values
1
:PMcurrentMeasurementEvent
- endOfEventDateTime = 2019-02-27T05:19:09
::MeasurementEvent
::Event
+ dateTime = 2019-02-27T05:18:16
:PMcurrentContext
::Context
:PMcurrentSensor
::MeasuringInstrument
:PointMachine
:Turnout
:PMcurrentMeasure
::Measurement
- typeOfMeasurementInterval = temporal
- intervalValue = 0.1
:PMcurrentValue
::Value
- ranks = { 0, ..., 532 }
- values = { 3.6, ..., 3.1 }
:PMcurrentUnit
::Unit
- SIunit = ampere
- SIunitSymbol = A
PM means PointMachine.PM means PointMachine.
Figure 4: Simplified instantiation example illustrating the measurement of point machines current consumption.
nificant growth in scientific literature on this topic,
and numerous concrete applications have emerged
in various sectors such as manufacturing, healthcare,
and transportation. DTs are promising tools to man-
age, monitor, control, simulate, and predict the be-
haviour of a real-world system.
In this paper, we first provided an overview of
these concepts by studying their historical back-
grounds and conducted a state of the art of their defini-
tions in literature. Based on our analysis, there is little
consensus regarding a generic, universal definition of
the DT concept across industry and academia. How-
ever, we emphasized that a clear definition is never-
theless required to guide the design and the produc-
tion of a DT. In addition, there are some frameworks,
methods, and standards to produce DTs but there is
currently no widely accepted generic or standardized
framework.
Furthermore, we underlined that a DT requires
models in order to be built, however among the ex-
isting frameworks, very few focus on the production
of model-driven DTs. Ontologies which are set of
concepts and axioms related to each other through se-
mantic and taxonomic relations, represent a specific
view of the world shared by a community. They of-
fer relevant solutions for analyzing domains, systems,
and products and formalize related computable mod-
els. The latter are of paramount importance to fur-
ther produce the digital representation of the system
or product to be digitally twined.
In this position paper, we argue that ontologies,
Model-Driven Engineering, and object-oriented prin-
ciples can be leveraged to produce model-driven Dig-
ital Twins. We propose a framework designed to as-
sist in the creation and development of DTs based on
these latter methods, hoping that it could help paving
the way towards a future standardized, generic frame-
work. We provide insights into the application of our
framework at SNCF R
´
ESEAU, the French Railway In-
frastructure Manager.
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