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  <front>
    <journal-meta>
      <issn pub-type="ppub">1613-0073</issn>
    </journal-meta>
    <article-meta>
      <article-id pub-id-type="doi">10.1016/J.PROCS.2024.09.251</article-id>
      <title-group>
        <article-title>Digital Product Passport: Initial System Architecture with Knowledge Graphs and Data Spaces</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Anastasiia Belova</string-name>
          <email>belova@dbis.rwth-aachen.de</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Viola Gallina</string-name>
          <email>viola.gallina@fraunhofer.at</email>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Artem Revenko</string-name>
          <email>artem.revenko@graphwise.ai</email>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Albin Ahmeti</string-name>
          <email>albin.ahmeti@graphwise.ai</email>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Workshop</string-name>
        </contrib>
        <contrib contrib-type="editor">
          <string-name>Digital Product Passport, Ontology, Knowledge Graph, Data Space</string-name>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Data Stream Management and Analysis (DSMA), RWTH Aachen University</institution>
          ,
          <addr-line>Ahornstr. 55, 52074 Aachen</addr-line>
          ,
          <country country="DE">Germany</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Fraunhofer Austria Research GmbH</institution>
          ,
          <addr-line>Vienna</addr-line>
          ,
          <country country="AT">Austria</country>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>Semantic Web Company (Graphwise)</institution>
          ,
          <addr-line>Vienna</addr-line>
          ,
          <country country="AT">Austria</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2023</year>
      </pub-date>
      <volume>246</volume>
      <fpage>0000</fpage>
      <lpage>0002</lpage>
      <abstract>
        <p>The European Commission proposes the Digital Product Passport (DPP) as a key instrument to promote more sustainable manufacturing and support the transition to a Circular Economy. The DPP is viewed as a promising tool designed to provide essential information about a product's origin and composition. This transparency enables consumers to make more informed purchasing decisions, facilitates recycling processes, and enhances the potential for product repair. Recent research supports the use of data spaces to enable the DPP concept, furthermore the CIRPASS project advocates using semantic technologies to organize DPP data assets. In this paper, we propose an initial architecture of a DPP system using data spaces and Knowledge Graphs. In the preparation of this architecture, we relied on previous research that analyzed the system's requirements and investigated the process of creating and issuing DPPs in the wood processing industry context. We illustrate the architecture using carbon footprint tracking as an example, considering it as a baseline for product manufacturing information that is relevant across various industries.</p>
      </abstract>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Following [
        <xref ref-type="bibr" rid="ref1 ref2 ref3 ref4">1, 2, 3, 4</xref>
        ], current sustainability eforts converge toward preparing several instruments
to achieve climate goals, including the Digital Product Passport (DPP). The DPP is envisioned as
an instrument to propagate information about manufactured products among participants of value
chains: Economic Operators (EOs) who put the final product on the market, their suppliers and the
customers of the EOs. The DPP should include “information on the origin, composition, and repair and
disassembly possibilities of a product, including how various components can be recycled or disposed
of at end-of-life” [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ], thus facilitating Circular Economy.
      </p>
      <p>
        Several papers [
        <xref ref-type="bibr" rid="ref6 ref7">6, 7, 8</xref>
        ] already advocate the usage of data spaces for sharing DPP information among
participants of value chains in a distributed and secure manner. Additionally, while current DPP-related
legislation does not suggest a specific data structure for organizing DPP data asset, the results of the
CIRPASS [9] research project support Knowledge Graphs (KGs) for representing DPP data assets.
      </p>
      <p>In this paper, we present the initial version of an architecture of a DPP system using data spaces
and KGs. This architecture is based on previous work on the requirements analysis [10] and on the
examination of a process of creating and issuing DPPs [11] for the wood processing industry. Reasoning
for such limitation of a scope was drawn from the prioritization of product groups by the EU Comission.
Examples of the prioritized groups are furniture, textiles and footwear, detergents, etc. Prioritized
product-specific DPPs will be defined by dedicated delegated acts before all other product groups.
Additionally, due to the lack of precise requirements for group-specific DPPs, we are using carbon</p>
      <p>CEUR</p>
      <p>ceur-ws.org
emissions tracking as an example to illustrate our DPP system. Refering to the global climate agenda,
we assume that product carbon footprint will be a key element of DPPs across all product groups.
Carbon footprint impacts in a direct or indirect way a number of the SDGs (Sustainable Development
Goals) established by the UN [12], namely SDG 12 (Responsible Consumption and Production), SDG
13 (Climate Action), SDG 15 (Life on Land), SDG 7 (Afordable and Clean Energy), SDG 9 (Industry,
Innovation, and Infrastructure), SDG 11 (Sustainable Cities and Communities). The use of KGs, however,
ensures adaptability and interoperability via FAIR principles, of the suggested architecture to future
scenarios.</p>
      <p>In the following, relevant research papers will be discussed in the Related Work section. Next, we
briefly present the context of our paper in order to describe the formalization process of the architecture
design, followed by the description of the architecture of the DPP system using KGs and data spaces
in Section 4. We also suggest our considerations in the discussion section (Section 5), also indicating
future work directions, before we conclude in Section 6.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Work</title>
      <p>
        The usage of data spaces for organizing a DPP system is advised by several papers [
        <xref ref-type="bibr" rid="ref6 ref7">6, 7, 8, 13</xref>
        ]. Several
papers suggest using Administrative Asset Shell (AAS) [14] or blockchain as part of the solution design
for DPP [
        <xref ref-type="bibr" rid="ref7">7, 15, 16, 17, 18</xref>
        ]. Several papers discuss ontologies for DPP [19, 20, 21]. In this paper, we focus
on the usage of ontologies and KGs as an adaptable and flexible approach to structuring the DPP data
asset. The work [22] provides an architecture design for a Digital Twin-based DPP for food products
emphasizing the product traceability aspect allowed by DPP. Another approach to the traceability
of products is provided in [23], where the authors discuss the role of Cyber-Physical Systems (CPS)
and an Internet of Materials online platform in increasing the transparency of materials life cycle.
The work [13] explores a DPP architecture for the footwear industry, focusing on the integration of
data space principles and on the usage of W3C Decentralized Identifiers (DIDs). Building upon the
previous work in [10, 11], this paper discusses how to use data spaces, ontologies and KGs to design an
architecture for a DPP system. To the best of our knowledge a comparable architecture has not yet
been discussed by a scientific paper.
      </p>
    </sec>
    <sec id="sec-3">
      <title>3. Context</title>
      <p>To formalize the architecture of our DPP system, we first examined the requirements for a DPP
system [10], where we defined a setting that outlines a use case scenario for the DPP system. The use
case scenario begins with a customer scanning a QR code on a product, which triggers the calculation
of the carbon footprint generated during manufacturing of this product. The requirements were
structured in seven groups: 1) product code scanning, 2) data exchange, 3) data representation, 4) carbon
footprint calculation, 5) security, 6) logging, monitoring, auditing and compliance, 7) documentation
and support. To meet the identified requirements, we suggested using Semantic Web technologies for
the representation of the DPP data assets and presented a first version of the DPP ontology. Additionally,
we considered using data spaces to exchange the carbon footprint information between an EO and
its suppliers. In the present paper, we are focusing on the first four groups of the requirements for
the initial architecture design, classifying them as functions of a minimal viable product within the
context of a DPP system. On the way towards the initial architecture, we also walked through a case
study at a furniture dealer and described the process of creating and issuing a DPP using data spaces
and ontologies [11]. This way, the first version of the ontology [ 10] has been expanded to include 15
classes, 10 object properties, and 19 datatype properties, along with 331 axioms like rdfs:subClassOf,
rdfs:domain and rdfs:range. Its structure integrates data from both the wood tracking and carbon
emission calculation use cases.</p>
      <p>Data Space  Data Space DCaotnanSepcatocre  DPP Service Supplier 
Uses Connector Tier 1</p>
      <p>DCaotnanSepcatocre  Data Space</p>
      <p>Data Space 
Connector</p>
    </sec>
    <sec id="sec-4">
      <title>4. Architecture</title>
      <p>In this section, we present the initial architecture design of a DPP system for product carbon footprint
tracking using KGs and data spaces, see Fig. 1. We describe how the system can be used by an EO, its
customers and suppliers. Direct suppliers of an EO are categorized as Tier 1, while those providing
intermediate materials to the Tier 1 suppliers are categorized as Tier 2 suppliers. We used the C4
model [24] to visualize the DPP system architecture, employing the component level approach to
represent the service backend and the customer’s frontend, while using the container level approach
to illustrate the remainder of the DPP system. By combining these levels, we intend to ofer both an
overview of the system and a more detailed view of the DPP service. We describe the architecture
workflow, using product carbon footprint tracking as an example.</p>
      <p>
        Additionally, in accordance with current legislation [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], EOs will be responsible for providing DPPs
for their products at the point of market entry. Therefore, we assume that the DPP service frontend for
EO’s customers, along with the related backend, will be deployed by the EO (cloud solution or local
infrastructure).
      </p>
      <sec id="sec-4-1">
        <title>4.1. DPP Service Frontend for Customers</title>
        <p>The DPP service frontend allows customers to scan a product’s QR code and access information about
the product, calculated in the backend. For example, if customers want to know the carbon emissions
generated during the product’s production, as well as the production of its intermediate components,
they can view a summary in the Product Info Display section of the interface. Customers do not need to
log in to the system to view basic information about the product. However, if controlling institutions, for
example, require more detailed information about the product or the composition of its carbon footprint,
they can log into the system to access a more comprehensive overview in the Product Info Display.
Therefore, the DPP system must accommodate diferent levels of access rights. In our architecture, we
propose storing and managing these access rights within the DPP Service Backend.</p>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. DPP Service Backend</title>
        <p>In the backend, the DPP service uses an SQL database to store login credentials and manage access rights
to the DPP data assets stored on the EO’s premises. Furthermore, the SQL database also has information
on how to attribute product IDs from the QR code to the related KGs. Using the information from the
SQL database, the Feedback Compilation component reads KGs from the EO’s storage and by traversing
them, summarizes the necessary information. For example, information on the carbon footprint will
be summarized using information from the corresponding KG of an EO, as well as KGs from all the
suppliers who delivered the intermediate materials for this product. To achieve this, the ontology
for product-related KGs is used to connect the product with its components. Thus, the KGs storage
of an EO should provide both the KGs about its own product manufacturing process and KGs about
(intermediate) product components from the EO’s suppliers. We base our approach on the assumption
that suppliers make carbon footprint information available upon product delivery, but may also provide
updates at later point in time. The Feedback Compilation component calculates the carbon footprint
for the individual products based on the up-to-date KGs when triggered by a customer’s request.</p>
        <p>To create KGs for production processes, the EO uses a corresponding ontology and relevant data
sources. Through mapping languages and ontological terms, and executed via a mapping engine, the
data sources are converted into triples and can be stored, for instance, in RDF format. The Exchange
and Store KGs component triggers the collection of KGs from the suppliers using the functionality of
data spaces.</p>
      </sec>
      <sec id="sec-4-3">
        <title>4.3. Collecting Data from Suppliers</title>
        <p>To collect data from suppliers, the EO uses a data space connector to establish agreements on data
exchange and negotiate the associated policies. The data assets from suppliers are then transmitted to
the EO in a peer-to-peer (P2P) manner, following the data space design. As a result, metadata about
the data exchange between participants is recorded by the data space connectors, while the data assets
themselves are exchanged securely. In terms of providing information on produced materials, suppliers
are also playing a role of the EO in B2B. Therefore, the components from the DPP Service Backend of
an EO should be deployed for their suppliers as well. These components should assist with compiling
summarized information about produced materials, creating KGs based on the suppliers’ data sources
and providing them to the EO using data space functionality. Suppliers of Tier 1 should also have
components to collect DPP data assets from their suppliers, which are mentioned as suppliers of Tier 2
in the Fig. 1.</p>
      </sec>
      <sec id="sec-4-4">
        <title>4.4. DPP Service Frontend for an EO</title>
        <p>To efectively manage the DPP service backend, the EO should also have a separate DPP service frontend,
distinct from the one used by customers. This frontend should enable the EO to initiate data exchanges
with suppliers and begin the process of mapping data sources to the KGs. Additionally, it should allow
for updating access rights in the SQL database and managing the relationship between a QR code and
data represented in the KGs. Suppliers should also have their own dedicated DPP service frontend.</p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Discussion and Future Work</title>
      <p>The initial architecture presented in this paper is based on the previous work [10, 11] on the DPP in the
wood processing industry. The scope and the limitations of the use case scenarios attributed to business
processes in this industry also extend to the architecture design in this paper, as the architecture design
was not investigated when applied to use cases in other industries. Hence, to confirm generalizability
of the suggested architecture, further research is needed to test the architecture’s applicability in other
domains.</p>
      <p>Additionally, while carbon footprint was used as an example for this architecture, the compilation of
the information in the backend of the service should also be tested for further data sets, as it may bring
more considerations on the components for the backend.</p>
      <p>Among further possible improvements is the introduction of greater granularity for the DPP
information. For example, information about a product should include not only manufacturing information,
but also information on product repair. Information from recycling companies can be helpful for the
product-related analytics from the EO’s perspective. Exploring how to integrate such data into the DPP
service will be an important area of future work, as repair or recycling information should be reflected
in the product DPP after an EO releases the product to the market.</p>
      <p>The current architecture design includes data mapping functionality, however it is also important to
extend the backend with SHACL rules for validating the structure of KGs.</p>
    </sec>
    <sec id="sec-6">
      <title>6. Conclusion</title>
      <p>The DPP is a crucial tool in advancing sustainability eforts: by providing essential data on the origin,
composition, and environmental impact of products, the DPP facilitates Circular Economy practices and
supports the global transition to more sustainable production and consumption patterns. This paper
presents an initial architecture for a DPP system using data spaces and KGs to manage and exchange
product data, with a focus on tracking carbon emissions as a key example. The proposed architecture is
designed to be flexible and scalable, allowing it to adapt to future scenarios through the use of KGs and
supporting distributed data sharing through data spaces.</p>
      <p>Future research will focus on refining the system and expanding its components to support additional
use case scenarios for collecting and presenting DPP information, such as material tracking or hazardous
materials, as well as information on product repair and recycling.</p>
    </sec>
    <sec id="sec-7">
      <title>Acknowledgments</title>
      <p>The presented work was carried out as part of the champI4.0ns project (https://www.champi40ns.eu),
which has received funding from the Austrian Federal Ministry for Climate Action, Environment,
Energy, Mobility, Innovation and Technology (BMK) (grant number 891793) and the German Federal
Ministry for Economic Afairs and Climate Action (BMWK).</p>
    </sec>
    <sec id="sec-8">
      <title>Declaration on Generative AI</title>
      <p>During the preparation of this work, the author(s) used GPT-4o LLM in order to: Grammar and spelling
check. After using these tool(s)/service(s), the author(s) reviewed and edited the content as needed and
take(s) full responsibility for the publication’s content.
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</article>