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    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Mat - Towards an Ontology-based Integration of Manufacturing and Simulation Processes for Fiber-reinforced Materials</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Patrik Schneider</string-name>
          <email>patrick-schneider@siemens.com</email>
          <xref ref-type="aff" rid="aff1">1</xref>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Maja Miličić Brandt</string-name>
          <email>maja.milicicbrandt@siemens.com</email>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Nicolas Christ</string-name>
          <email>nicolas.christ@iwm.fraunhofer.de</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Martin Kördel</string-name>
          <email>martin.koerdel@siemens.com</email>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Niklas-Alexander Tofert</string-name>
          <email>niklas-alexander.toffert@siemens.com</email>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Fraunhofer IWM</institution>
          ,
          <addr-line>Freiburg</addr-line>
          ,
          <country country="DE">Germany</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Siemens AG</institution>
          ,
          <addr-line>Munich</addr-line>
          ,
          <country country="DE">Germany</country>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>Technische Universität Wien</institution>
          ,
          <addr-line>Vienna</addr-line>
          ,
          <country country="AT">Austria</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2025</year>
      </pub-date>
      <abstract>
        <p>The rapidly expanding market for composite materials, driven by applications in automotive, aerospace, and renewable energy, requires a comprehensive framework to describe fiber-reinforced materials. Although versatile, these materials lack standardized data representation, hindering cross-scale integration from material characterization to manufacturing. The OntOMat project aims to bridge this gap by developing a novel ontological framework grounded in FAIR data principles. Through ontology engineering, it enables the collection, linkage, and analysis of data across various processes, focusing on fiber-reinforced polymers. This approach allows for the optimization of material microstructures for enhanced stability and recyclability.</p>
      </abstract>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        The market for composite materials is growing at double digit percentages annually [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ], as composite
materials allow lightweight applications in the construction of automobile, train, ship, and aircraft,
as well as renewable energy, such as wind turbine blades. Due to the non-standardized nature of
composites and in particular fiber-reinforced materials, thousands of possible material systems need to
be described. Currently, a harmonized description including cross-scale relationships between material,
process, and component is not available for them. In addition, there is insuficient data integrity with
respect to material characterization, simulation, and manufacturing processes. The implementation
of FAIR data principles [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ] and semantic technologies, such as ontologies, should allow us to describe
these material systems and represent complex cross-scale relationships. This is intended to open up
previously unusable potential for data-driven material development and process optimization, as well
as the establishment of material cycles.
      </p>
      <p>The main goal of the OntOMat project is to develop a novel ontological framework that allows the
implementation of FAIR data principles using ontology engineering. This should allow us to collect,
link, and analyze data arising from material data sheets, but also from characterization, production,
and simulation processes which are collected for a variety of material systems. In terms of material
systems, the focus is on fiber-reinforced polymers. The linking of data and parameter arising from these</p>
      <p>CEUR
Workshop</p>
      <p>ISSN1613-0073
processes should then allow us to compare and optimize a material’s microstructure for operational
stability and recyclability. The scope can be directly derived from the project goal and includes the
creation of an ontology for (a) fiber-reinforced materials and their characteristics, (b) the manufacturing
and characterization processes of these materials, and (c) the simulation processes to determine certain
characteristics or behavior. In this paper, we first present our ontology development methodology
(Section 3), then give the details of the OntOMat ontology (Section 4) and discuss limitations and future
work (Section 5).</p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Work</title>
      <p>For an extensive survey of ontologies in materials science and engineering, we refer to [3] and give
more details on the relevant top- and midlevel ontologies in Section 3. From the domain-level ontologies
presented in [3], the EMMO General Process Ontology (GPO), the Semantic Materials, Manufacturing
and Design1 (SEMMD) ontology, the Additive Manufacturing Ontology (AMONTOLOGY), Ontology
for Simulation, Modelling, and Optimization (OSMO), Dislocation Simulation and Model Ontology
(DSIM), Atomistic Simulation Methods Ontology (ASMO), Metadata4Ing Ontology (M4I), and Material
properties ontology (MAT) covers the same domains as our work. Since the OntOMat project is part of
Platform MaterialDigital2 that provides a top-level ontology with the BFO[4] and a mid-level ontology
with the PMD Core Ontology3 (PMDCo), we focus only on ontologies that align with the BFO or
PMDCo, since alignments with other top-level ontologies are beyond the scope of this work. The
SEMMD ontology is concerned with the same focus and is already BFO aligned, but any documentation
regarding its use is missing. Ontologies that describe either composite materials or VDI/VDE 3682
Formal Process Language (VDI 3682 language) are harder to find. Polymer membrane research and
related laboratory experiments are described in the PolyMat ontology [5], but the ontology does not
seem expressive enough to capture, e.g., complex simulations. An initial ontology for the VDI 3682
language was introduced in the work of [6], which we considered in our ontology design. However, the
work of [6] missed certain design elements, such as process decompositions and alignment with any
top-level ontology.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Ontology Development</title>
      <p>We apply the “Simple Knowledge Engineering Methodology” of [7] to develop our ontology. It ofers
good guidelines for an agile modeling process. For brevity, we recapture the main steps introduced by
the authors of [7] and give more details in the following subsections:
1. Domain and scope of the ontology that includes competency questions for narrowing the scope;
2. Reuse of existing ontologies that includes an alignment with mid- or top-level ontologies;
3. Collect important terms and define classes and their hierarchies in the ontology, which can be
addressed by top-down, bottom-up or combined approach;
4. Define properties of classes including “slots” such as cardinality and domain/range;
5. Define instances, which includes generic instances that should be available for every user, but
also includes illustrating examples.</p>
      <p>Note that above steps are a non-linear process of incremental interactions (in particular steps 3. to
5.). Hence, the terms for a specific topic are collected by domain experts, mainly material scientists but
also simulation engineers, stored in an intermediate source, which then builds the base to define classes
and properties. The authors then present the results including class and property hierarchies to the
aforementioned domain experts for evaluation.</p>
      <sec id="sec-3-1">
        <title>1https://github.com/cpauloh/semmd 2https://www.materialdigital.de/ 3https://materialdigital.github.io/core-ontology/index-de.html</title>
        <sec id="sec-3-1-1">
          <title>3.1. Competency Questions</title>
          <p>The first step of [ 7] relates to the collection of more than 50 competency questions with the experts of
the OntOMat partners. They are categorized by “material testing/characterization”, “manufacturing
process and equipment”, “physical product traceability”, “material consumption”, “product life cycle
and design”, and “material testing/characterization”. In the following, we present a list of exemplary
competency questions (CQs) and expected exemplary answers:</p>
          <p>Competency question Expected answer
ebWrethyui?cshedchfoarraactceerriztaaitnionmmateetrhiaoldpsrcoapn- cqCmhueaaartrtneaarticiinaftyelm.,rieza.atget.ir,oiatnhletperfibcoheprneirvqtoiueleussmc.aeAncbCoenTqteusncatannotiffiecdaanbcyboemspupesocesidificteto</p>
        </sec>
      </sec>
      <sec id="sec-3-2">
        <title>What characterization methods can be applied within a manufacturing process?</title>
      </sec>
      <sec id="sec-3-3">
        <title>The existing processes show that digital holography is an in-situ process operator.</title>
      </sec>
      <sec id="sec-3-4">
        <title>Specified material information including the material prop</title>
        <p>erties and values as well as defined geometry to be modeled
aWshpaetcpificarsaimmueltaetrisoanr?e required to run
ccaohlonanndgiictwiso,intahsrenthneeeedepdhteoydsb.iecIsndteaofindbeddeitaaionnnad,lytthhzeeedgl,oeeao.dgms.,eastntrryducnbtoeueurdnasldmtaoreybe discretized in order to numericial solve the diferential
equation.</p>
        <p>How can data from the characteriza- Test results can be reduced to efective parameters, e.g.,
tion be implemented into the simula- the modulus of elasticity, which is then used in a suitable
tion model? numerical model.</p>
        <p>Durability means change of material properties values over
What contributes to product durabil- time. Durability therefore depends on the operational
conity? ditions applied as well as the impact on specific material
properties.</p>
        <p>There is no clear relation between material class and
simuWhich simulations can be used for a lation technique, but there is a relation between simulation
certain material system? domain and physics to be studied for a certain material
class.
onWrehesdiametdulfcaohtriaoarnas?cpteecriizficamtioatneriadlamtaodaerle
ifcenThrehtdayer.amvTcahatletueerepirszia.aarltaimmonoetdteeerclvhraenlqiuqueuisreecssatnchebarettaqrieuntarpnieatvrifaeymdmfertoaemtresrstipaolebcpeirficodpe-sWpehcaitficsmubatsetarinaclecslaasrse? contained in a aAmsefibtnhetre.-rmeaintrfioxrcaenddecpaorxbyonr
efibseinrsh(a7s78e2p-o4x2y-5r)eassinth(6e1r7e8in8-f9o7r-c4e)eWrthieast faorer athsepreeclieficvmanattemriaatlecrliaaslsp?rop- tnThueesmtmerroeisdcuuallltumsscooadfneelb.laestriecdituyc,ewdhtiocheifesctthiveenpuasreadmientearssu,iet.agb.,le
cSmohanonwtuenftahtceotuinmrimpnagactpteroroifacrleespcsyreocslp?eedrtmieastearniadl tscCeiogornnimasitlficpaaacnnortetn.ldytetdnoetv,vieairvtgeeinnfoirmfmtahtaeetreimraialaslt,setcrhioaenltpacroinomipnpegrotrsyeitcivyoacnllueidessmkceaap-nt
Based on the competency questions, we can derive important concepts, including material properties
and compositions, as well as a model for simulation, manufacturing, and characterization processes,
including process parameters and results, which play a crucial role for answering the CQs. We also
provide the full list of CQs in our project’s Gitlab repository.</p>
        <sec id="sec-3-4-1">
          <title>3.2. Ontology Reuse</title>
          <p>The second step of [7] is the alignment with a mid-/top-level ontology. Ontology reuse is along a pyramid,
where the top-level has the highest abstraction level and are usually called upper ontologies. Examples
are Basic Formal Ontology (BFO) [4] and Industrial Data Ontology (IDO) [8] with a focus on industrial
data. Below are mid-level ontologies that describe a specific technical domain such as Quantities, Units,
Dimensions and Data Types Ontologies (QUDT)4 or PROV Ontology (PROV-O) [9] which are often
orthogonal to upper ontologies. Domain ontologies, such as Elementary Multiperspective Material
Ontology (EMMO) [10]5, describe a specific scientific or industrial domain, where the OntOMat ontology
would be one particular domain.</p>
          <p>As the OntOMat project is situated at the intersection of industrial data/processes and material
science, the IDO ontology is a natural starting point for modeling, since simulation and manufacturing
processes are an important scope of the vocabulary. Another option would have been the PMDCo 1.0
ontology based on PROV-O, which provides some useful top-level concepts, such as Activity, but it
lacks the coverage and standards compliance to known top-level ontologies such as BFO. With the
publication of the PMDCo 3.0 ontology that is based on the BFO the coverage and standards compliance
is given, and in the discussion we will outline the path towards a tighter integration with the PDMCore
3.0.</p>
        </sec>
        <sec id="sec-3-4-2">
          <title>3.3. Conceptualization</title>
          <p>For the OntOMat ontology in most cases, the IDO classes and properties build the highest level of
class hierarchies, whereby the classes lis:PhysicalArtefact, lis:PhysicalObject, lis:Quality,
lis:Activity, and lis:InformationObject are our anchor points. An important characteristic of
IDO modeling is the distinction of any object (besides information) between lis:Specified, i.e., any
abstract representation of an object such as a definition or simulation model, and lis:Actual, i.e.,
objects that exist or existed at one point.</p>
          <p>The third step of [7] is the collection of important terms that lead to classes and related properties.
Initially, we manually collected terms based on standards and guidelines with the support of domain
experts. For example, experts suggested a material classification according to the IEC 62474 standard
[11] and a formalized process description (FPD) according to the VDI/VDE 3682 guidelines [12] as
important sources. For material qualities, the domain experts suggested a list of 150 relevant qualities
based on literature research, which we extended with units and symbolic representations. Material
classes and qualities were collected as term lists and taxonomies in newly created spreadsheets, while
processes, states, and operators of the FPD were directly extracted from the text-based guidelines. With
the fourth step, we bring all the pieces together, where we created an initial version of the ontology
formulated in OWL 2 DL6. We decided on a modular approach that creates a separation between terms
related to material products, to material and properties classes, and to processes that include simulations.
Each module was validated by our domain experts for content-related correctness, which led to several
rounds of improvements. The ontology described in the next section represents the result after the
completion of the fourth step.</p>
        </sec>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. The OntOMat Ontology</title>
      <p>The OntOMat ontology (OMO) is conceptually split into three tiers, where the top level is currently
IDO, the middle level is a handcrafted structure with the support of domain expert, and the lowest level
is automatically generated based on two industry standards concerning material classes and process
descriptions. An important part are material classes and material qualities, i.e., material properties,
which are then used to define material products based on these material classes. Another important</p>
      <sec id="sec-4-1">
        <title>4https://www.qudt.org/ 5EMMO also introduces its own top-level and mid-level vocabulary, rather than re-using existing ones. 6https://www.w3.org/TR/owl2-overview/</title>
        <p>part describes the characterization, manufacturing, and simulation processes from an “a posterior”
perspective, thus the process path (e.g., based on observations stored in logs) of the respective process
is captured, and (currently) not the process plan modeled “a priori”. Figure 1 shows the three tiers,
where the color of the box represents thematic modularization, the white arrows represent the subclass
relations, and the black arrows define the domain / range of object properties. The ontology is published
on the MaterialDigital Github repository under https://github.com/materialdigital/ontomat-ontology.</p>
        <sec id="sec-4-1-1">
          <title>4.1. Physical Products, Material Classes, and their Property Classes</title>
          <p>With OMO, we introduce a duality between “real” physical products represented by PhysicalProduct
and abstract material classes simply called Material. A physical product is made of one or more
materials represented by material classes and is connected by the hasMaterial object property to
a physical product.7 Measurable material properties are connected by hasMaterialQuality with
the domain lis:PhysicalObject (thus any physical object can have material properties) and the
range of IntensivePhysicalProperty and subclasses that define types of material properties. Specific
properties can be “real” properties of a physical product, which are measured as values of the designated
specimen, or “abstract” properties of the material obtained from a product datasheet / publications.
This duality allows us to manage the known material properties for material classes and their values
only once and reuse them for every specimen. For example, the density of the material (class) gold is
approximately 19.3 g/cm3, but the density of a specific gold bullion is measured as 19.2 g/cm 3 due to
some contamination.</p>
          <p>The hierarchy of material classes starts with the Material class with a fixed set of subclasses derived
from the IEC 62474:2018 standard taxonomy. The left nodes in the IEC taxonomy are automatically
generated based on the standard spreadsheet shown in Figure 2a.8 However, the IEC 62474:2018 standard
misses some concepts to describe fiber-reinforced materials:
7hasMaterial is a subproperty of IDO’s lis:hasMaterialPart, which has the domain lis:Compound. We extended the
domain to include Material, since the ontology should also cover composites.
8https://std.iec.ch/iec62474/iec62474.nsf/Index?open&amp;q=161936
(a) Material classes
(b) Material properties</p>
          <p>• Classes representing fiber-reinforced composite materials are missing, only filled composites are
mentioned;
• Only one class for gases and liquids is defined, whereby a clear separation between mixtures and
pure gases (similarly for liquids) is missing;
• Thermosetting polymers, such as melamine formaldehyde (MF) and vinyl ester (VE) are not
considered;
• The CAS registry number is missing, which is used to identify the most prominent chemical
substance in a material.</p>
          <p>With the support of our domain experts, we extended and refined the IEC 62474:2018 taxonomy,
thus introducing the paired classes for gas (pure / mixture), liquids (pure / mixture) and solid materials
(homogeneous / heterogeneous), as well as dropping all unspecified classes such as “other unfilled
thermoplastics”, which are covered by their superclasses. For example, we introduced the new classes
SolidHomogeneousMaterial and SolidHeterogeneousMaterial, where from the latter we derived
the subclass CompositeMaterial. This subclass is central to OMO and acts as the domain for the
following object properties that define possible composite structures:
• hasMatrixWith denotes the matrix material, e.g., epoxy resin;
• reinforcedWith denotes the material that is used for reinforcement, e.g., fibers;
• filledWith denotes the material that is used as a a filler, e.g., air.</p>
          <p>Note that for any of the above properties, we also added the transitive closure using a transitive
property, since a material structure can have several levels of nesting. For example, we added the
property hasMatrixWithTransitive for the hasMatrixWith. Similarly to the material class hierarchy,
our experts conducted an extensive literature analysis to collect suitable property classes that were
recorded in a reference spreadsheet. The spreadsheet defines the QUDT unit, a commonly used symbol,
including aligned index usages, e.g.,  1, with respect to direction and symmetry class, e.g., isotropic.
An excerpt of the reference spreadsheet is given in Figure 2b and again the respective subclasses
such as ElasticModulusE1 for “elastic modulus E1” are generated and aligned to the mid-tier, e.g.,
ElasticProperty, automatically.</p>
        </sec>
        <sec id="sec-4-1-2">
          <title>4.2. Composite Material Classification</title>
          <p>An objective of the OntOMat project is to provide an automatic classification of composite materials
according to the structure of these materials. As shown in Figure 3, the classification of composite
materials resembles the overlap of two hierarchies starting with CompositeMaterial, namely a
matrixbased hierarchy (starting with MatrixBasedCompositeMaterial) and a reinforcement-based hierarchy
starting with ReinforcedCompositeMaterial. Both hierarchies are joined again on the leaves, where
the outcomes of the classification are added. For example, the leave class FiberReinforcedEpoxyResin
is sub-class of PolymerMatrixCompositeMaterial and also of FiberCompositeMaterial.
Having a wide range of possible
materials that can act as a matrix
(examples of suitable polymer classes are
shown in Figure 2a) and act as
reinforcements or fillings (such as Carbon),
we introduced a classification system
based on equivalence axioms. Our
intuition is the following; on left-hand
side of the equivalence is the class
for the material system, for instance
FiberReinforcedEpoxyResin, and on
the right-hand side is an intersection
of CompositeMaterial, a existential re- Figure 3: Partial rendering of the composite material
classtriction on hasMatrixWithTransitive, sification.
in this case, EpoxyResin, and another
existential restriction on reinforcedWithTransitive on Material. The generic Material class
is used, since any material class could act as a reinforcement. The resulting equivalence
axiom: FiberReinforcedEpoxyResin ≡ (CompositeMaterial ⊓ ∃hasMatrixWith.EpoxyResin ⊓
∃reinforcedWith.Material), with  ( hasMatrixWith) and  ( reinforcedWith) is written in RDF
1.1 Turtle9 notation as:
1 ontomat : F i b e r R e i n f o r c e d E p o x y R e s i n owl : e q u i v a l e n t C l a s s
2 [ owl : i n t e r s e c t i o n O f (
3 ontomat : C o m p o s i t e M a t e r i a l
4 [ r d f : type owl : R e s t r i c t i o n ;
5 owl : onProperty ontomat : h a s M a t r i x W i t h T r a n s i t i v e ;
6 owl : someValuesFrom ontomat : EpoxyResin
7
8
9
10
11 ]
12 ) ;
13 r d f : type owl : C l a s s
14 ] ;
15 dcterms : i d e n t i f i e r ”O−402” ;
16 r d f s : l a b e l ” F i b e r − r e i n f o r c e d EpoxyResin ( EP ) ” .</p>
          <p>]
[ r d f : type owl : R e s t r i c t i o n ;
owl : onProperty ontomat : r e i n f o r c e d W i t h T r a n s i t i v e ;
owl : someValuesFrom ontomat : M a t e r i a l</p>
          <p>Listing 1: Example of an equivalence axiom with the OMO prefix ontomat:.</p>
          <p>Taking the axiom from the listing above, reinforcedWithTransitive is replaced with
filledWithTransitive to define filled composite material classes. The Material class could be
replaced with Carbon to define more specialized systems such as CarbonFiberReinforcedEpoxyResin.
Note that these axioms are automatically generated based on the spreadsheets shown in Figure 2a,
where the “ClassName” column is parsed to extract the type of reinforcement and the matrix class.</p>
        </sec>
        <sec id="sec-4-1-3">
          <title>4.3. VDI/VDE 3682 Formal Process Language</title>
          <p>Despite several standards that are used to model processes, e.g., business process modeling and notation
(BPMN),10 no language captures all the aspects of technical processes that occur in engineering /
industry applications, including their digital representation. The authors of the VDI/VDE 3682 Formal
Process Language (VDI 3682 language) outline the following aspects that should be captured by a
process language [12] used in engineering / industry applications:</p>
        </sec>
      </sec>
      <sec id="sec-4-2">
        <title>9https://www.w3.org/TR/turtle/ 10https://www.omg.org/spec/BPMN/2.0.2/</title>
        <p>(a) An single process step and its decomposition
(b) The eight graphical symbols</p>
        <p>• Modeling the life cycle of a technical systems, including its digital representation (usually called
the digital twin);
• Applicable to all kinds of processes including technical / non-technical, continuous / batch
processes in all fields of technical applications;
• Simple, neutral regarding the industry, and easily understandable;
• Containing all information necessary for engineering and normal operation based on modern IT
tooling and methods;</p>
        <p>The resulting VDI 3682 language is a visual language based on a predefined set of eight symbols
(shown in Figure 4b) that include three states, a system limit (dashed frame), a process operator (green
rectangle) and a technical resource (gray rectangle). The three kinds of states are product (red circle),
energy (blue, rhombus), information (blue hexagon), which act as input and output of a process operator
and are required to evaluate the operator. As shown in Figure 4a left, a process flow is always an
alteration between states and process operators with reference to the technical resources used in that
operator. In addition, the modeler has the choice to define parallel (the default) or alternatively running
(similar to an XOR condition) process flows. A powerful feature of the VDI 3682 language is the ability
to decompose a process operator into a new subprocess (shown in Figure 4a right), thus introducing
modularity similar to functions in programming languages. The VDI 3682 guideline also introduces an
UML-based data model and XML-based rendering of the visual language. We believe that the UML-based
data model is a helpful sketch but is ambiguous regarding its serialization. In the second part of the
guideline, the authors introduced an XML-based representation, which is suficient for simple processes.
However, this representation is underspecified and does not capture the full complexity of VDI 3682
process flows, for example, cyclic flows or subprocesses. Similarly to the authors of [ 6], we suggest that
an ontology-based representation for the VDI 3682 symbols and workflows, as well as an RDF-based
representation of (executed) workflows, are the most promising methods to capture it. Furthermore,
material states can be defined more fine-grained by material classes, and similarly information states
can be modeled by document and process parameter classes.</p>
        <p>The ontology represented by [6] does not reuse any top-level ontology. Thus, we anchor our
representation of the VDI 3682 language in IDO, where processes and operators are subclasses of lis:Activity,
information states are directly mapped to lis:InformationObject, and production assets are
subclasses of lis:PhysicalArtefact. As shown in Figure 5, the class VDIProcess is directly derived
and includes subclasses such as ManufacturingProcess and SimulationProcess. Similarly the class
VDIProcessOperator is directly derived with the subclasses MoldingOperator, and SimulationRun.
A production asset is captured by VDIProductionAsset with subclasses such as Workstation and
SimulationTool. A larger challenge is to capture the process flows and alteration of the input/output
states. A complete process workflow is called VDIProcess and is a wrapper that includes the system
limit, which has one or more hasOperator properties pointing to its initial VDIProcessOperators. The
properties next (and the inverse previous) define the next (and previous) evaluation order of a specific
operator. The three states are linked to a VDIProcessOperator by the following object properties,
whereas at least one state is required to be linked:
• product state: by hasInputProduct and hasOutputProduct to PhysicalProduct thus
connecting products and their related materials to processes;
• information state: by hasInputInformation and hasOutputInformation linking to
VDIInformationObject, which has a property source to underlying documents and can combine
several process parameter or result items by the property contains;
• energy state: by hasInputStream and hasOutputStream to VDIEnergyStream class;
• technical resource: by producedBy with the domain ProductionAsset.</p>
        <p>Our representation does not fully align with the VDI 3682 language, as some definitions seem
redundant. We have not introduced any concept for the system border, since the VDIProcess represents
the border. For example, any state connected directly to VDIProcess, e.g., by hasInputProduct, is
the interface to the exterior of a process. Note that the VDI 3682 language does not have a next and
previous relation to represent an explicit process flow. Hence, we introduced the next and previous
object properties, since they should simplify the query of explicit process flows using property paths.
The next property can be deduced by the property chain: hasIP− ∘ hasOP ⊑ next, where hasIP, hasOP
and next represents hasInputProduct(y,z), hasOutputProduct(x,z), and next(x,y).</p>
        <sec id="sec-4-2-1">
          <title>4.4. Usage Example</title>
          <p>To illustrate the use of the OMO, we give a simple example of a knowledge base (KB) that describes
a test specimen used in the OntOMat project. A test sample is produced by resin transfer molding
(RTM), where a liquid epoxy resin is injected under pressure into a closed mold containing dry glass
ifber, which is then cured to form a composite part, i.e., the resulting product.</p>
          <p>First, we describe the material and its composition, and add the material quality density and its value
measured in a material characterization process:
1 : epoxy −M_LY556_GFKUD0_01 r d f : type ontomat : C o m p o s i t e M a t e r i a l ;
2 r d f s : l a b e l ” Siemens Epoxy GFK UD” ;
3 ontomat : manufacturedBy ” Siemens Technology ” ;
4 ontomat : hasMatrixWith : a r a l d i t e _ L Y _ 5 5 6 ;</p>
          <p>Second, we outline the RTM process and a single process operator according to the VDI 3682 standard.</p>
          <p>Note that the RTM process has nine operators, but we only show the first one for brevity:
1 : epoxy −M_LY556_GFKUD0− M a t e r i a l F o r m i n g −Main r d f : t y p e ontomat : M a n u f a c t u r i n g P r o c e s s ;
2 r d f s : l a b e l ” Epoxy GFK UD P r o c e s s ” ;
3 ontomat : h a s O p e r a t o r : epoxy −M_LY556_GFKUD0− M a t e r i a l F o r m i n g −PO01 , : epoxy −M_LY556_GFKUD0−</p>
          <p>M a t e r i a l F o r m i n g −PO05 ;
ontomat : h a s I n p u t P r o d u c t : a r a l d i t e _ L Y _ 5 5 6 − product −1 , : a c r y s t a l _ L _ 4 0 4 0 _ B B − product −1 ;
ontomat : h a s O u t p u t P r o d u c t : epoxy −M_LY556_GFKUD0_01− f i n a l − p a r t .
4
5
6
7 : epoxy −M_LY556_GFKUD0− M a t e r i a l F o r m i n g −PO01 r d f : t y p e ontomat : V D I P r o c e s s O p e r a t o r ;
8 r d f s : l a b e l ” Epoxy GFK UD p r o c e s s f o r c o m p r e s s i n g ” ;
9 ontomat : h a s I n p u t P r o d u c t : a r a l d i t e _ L Y _ 5 5 6 − product −1 ;
10 ontomat : h a s O u t p u t P r o d u c t : a r a l d i t e _ L Y _ 5 5 6 − product −2 ;
11 ontomat : producedBy : p r e s s u r e _ v e s s e l − a s s e t −01 ;
12 ontomat : n e x t : epoxy −M_LY556_GFKUD0− M a t e r i a l F o r m i n g −PO05 .</p>
          <p>Third, we modeled a generic simulation process according to the VDI 3682
standard. This process model can capture several types of simulations, such
as structural mechanics simulations, using ifnite element analysis software.
As illustrated in Figure 6, a generic
simulation process can be described as a
preprocessing, a simulation (that is, running
the simulation), and a postprocessing
operator. A material instance (e.g., a specific
ifber-reinforced epoxy resin), a geometry
(e.g., the shape based on a given standard)
and a set of input parameters are the
input states, while the simulation results
(e.g., additional material qualities),
information (e.g., logs), and a simulated
specimen (of a material) are the output states
of the simulation process. Note that we
deliberately modeled a material instance
as a (specified) physical object instead of
an information object. Furthermore, this
process model does not sufice to describe
multi-scale simulation processes, which
could be seen as a parent process with
the above simulation process as one of
several compositions. Figure 6: A generic model of a simulation process.</p>
          <p>From this simple example, one can see
that it is not feasible to create and maintain instances for more complex processes manually. Thus, the
next step in the OntOMat project is to provide tools for data onboarding of VDI 3682 process models
created with the FPB.JS tool11 of Fay et al. [13]. Additional sources such as input parameter, source,
and log files that describe the boundary conditions or process parameters of a specific simulation run
can be used to enrich the imported models.</p>
        </sec>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Discussion and Conclusion</title>
      <p>In this paper, we outline the ontology development process in the OntOMat project and introduce
the main elements of the resulting OntOMat ontology. Describing base material classes and material
properties is as expected, but modeling and import of the IEC 62474:2018 standard, as well as the related
equality axiom-based classification of composite materials, based on their base materials, is a novel
approach to material classification. At the core of the OntOMat ontology is the representation of the
VDI 3682 (Formal Process Language) standard, which is a visual language to describe any kind of
real and digital processes. Due to the complexity of the VDI 3682 standard, it is not trivial to find an
appropriate semantic representation of it. However, this should allow us to describe complex multiscale
simulations, integrate the results of these simulations, and align them with underlying material systems.</p>
      <p>We recognize that the current ontology has limitations and still needs to be extensively evaluated
with real characterization, simulation, and manufacturing processes. One limitation is that we do
not fully support parallel process flows, which require additional concepts such as synchronization
points. The axioms for automatically deducing the object properties next / previous and the automatic
classification that the processing states are in the limit of the system are yet missing. Furthermore,
technical resources are coarse-grained modeled, and a taxonomy based on the ISA-9512 standard would
be valuable.</p>
      <p>The future work focuses on several directions: (a) finalizing the ontology addressing the above
limitations and a complementary alignment to the PMD Core Ontology; (b) providing an extensive
tool set for injecting data for specific material systems based on input spreadsheets; (c) supporting the
integration of existing VDI 3682 visual process modeling tools; (d) in addition to an existing SPARQL
interface, also provide a GenAI-based copilot to interact with the knowledge base combining the
ontology with instances for each material system.</p>
    </sec>
    <sec id="sec-6">
      <title>Declaration on Generative AI</title>
      <p>During the preparation of this work, the authors used Writefull for Overleaf13 to check grammar, spell
check, and paraphrase to improve the readability of the text. The authors reviewed and edited every
suggested content improvement and assume full responsibility for the content of the publication.</p>
    </sec>
    <sec id="sec-7">
      <title>Acknowledgements References</title>
      <p>This work was supported by the OntOMat project (no. 20) supported by the MaterialDigital initiative
of the Bundesministerium für Bildung und Forschung.
11https://github.com/HamiedNabizada/FPB.JS
12https://www.isa.org/standards-and-publications/isa-standards/isa-95-standard
13https://www.writefull.com/writefull-for-overleaf</p>
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