=Paper= {{Paper |id=Vol-2060/mekes3 |storemode=property |title=Ontology Engineering for Collaborative Embedded Systems – Requirements and Initial Approach |pdfUrl=https://ceur-ws.org/Vol-2060/mekes3.pdf |volume=Vol-2060 |authors=Constantin Hildebrandt,Sebastian Törsleff,Torsten Bandyszak,Birte Caesar,Alexander Ludewig,Alexander Fay |dblpUrl=https://dblp.org/rec/conf/modellierung/HildebrandtTBCL18 }} ==Ontology Engineering for Collaborative Embedded Systems – Requirements and Initial Approach== https://ceur-ws.org/Vol-2060/mekes3.pdf
         Ina Schaefer, Loek Cleophas,  Michael
                                Ina Schäfer,    Felderer
                                             Dimitris    (Eds.): Workshops
                                                      Karagiannis             at Modellierung
                                                                  et. al. (ed.): Modellierung 2018,
                                                                                              2018,
        Modellierung in der Entwicklung von  kollaborativen eingebetteten  Systemen  (MEKES)
                  Lecture Notes in Informatics (LNI), Gesellschaft für Informatik, Bonn    2018 571

Ontology Engineering for Collaborative Embedded
Systems – Requirements and Initial Approach

C. Hildebrandt 1, S. Törsleff1, T. Bandyszak2, B. Caesar1, A. Ludewig1, A. Fay1


Abstract: Collaborative embedded systems (CES) heavily rely on information models to
understand the contextual situations they are exposed to. These information models serve different
purposes. First, during development time it is necessary to model the context for eliciting and
documenting the requirements that a CES is supposed to achieve. Second, information models
provide information to simulate different contextual situations and CES´s behavior in these
situations. Finally, CESs need information models about their context during runtime in order to
react to different contextual situations and exchange context information with other CESs.
Heavyweight ontologies, based on Ontology Web Language (OWL), have already proven suitable
for representing knowledge about contextual situations during runtime. Furthermore, lightweight
ontologies (e.g. class diagrams) have proven their practicality for creating domain specific
languages for requirements documentation. However, building an ontology (light- or heavyweight)
is a non-trivial task that needs to be integrated into development methods for CESs such that it
serves the above stated purposes in a seamless way. This paper introduces the requirements for the
building of ontologies and proposes a method that is integrated into the engineering of CESs.
Keywords: Collaborative Embedded Systems, Ontology Building, Requirements


1     Introduction
Embedded systems are deeply integrated into their context, since they have to sense
contextual situations by means of sensors and interact with objects in the context by their
actuators. However, due to the rising complexity of the tasks assigned to embedded
systems, modern embedded systems are increasingly interconnected, and collaborate
with other systems to achieve common goals that a single system could not achieve on
its own. In this paper, we refer to such systems as collaborative embedded systems
(CESs). For example, in the manufacturing domain, several application scenarios of the
platform “Industrie 4.0” [PLA16@] illustrate the collaboration of embedded systems. In
the application scenario “Order Controlled Production” for instance, CESs are supposed
to autonomously manufacture a customer order from inquiry to finished product. In the
energy domain, CES are of growing importance as well, as decentralized control
solutions based on distributed intelligent components are considered a key enabler for
the “Energiewende” [De12@]. As a result, much research in the fields of distribution
grid automation and virtual power plants is concerned with the utilization of CESs that
collaborate with one another to achieve common goals. In both examples, the CES are
1
  Helmut-Schmidt-University, Institute for Automation Technology, Holstenhofweg 85, 22043 Hamburg,
  {c.hildebrandt, toersles, caesarb, ludewiga, a.fay}@hsu-hh.de
2
  University of Duisburg-Essen, paluno – The Ruhr Institute for Software Technology, Gerlingstraße 16, 45127
  Essen, Torsten.Bandyszak@paluno.uni-due.de
58 Constantin Hildebrandt, Sebastian Törsleff, Torsten Bandyszak, Birte Caesar,
Alexander Ludewig,
2 C. Hildebrandt,    Alexander
                  S. Törsleff,    Fay
                               T. Bandyszak, B. Caesar, A. Ludewig, A. Fay

required to exchange complex information about the context they are embedded in.
Furthermore, they need a common understanding regarding the syntax and semantic that
is being exchanged. Hence, there is an imminent need for information models that allow
for modelling the context of different CESs in a unified manner. Underlying each
information model is an ontology, i.e., a theory about the real-world objects to be
modelled [STW03]. According to [JU99], an “ontology may take a variety of forms, but
it will necessarily include a vocabulary of terms and some specification of their
meaning. This includes definitions and an indication of how concepts are inter-related
which collectively impose a structure on the domain and constrain the possible
interpretations of terms.” Ontologies have already proven a promising candidate for
modeling complex contextual relations in the domain of context-aware applications
[BBH+10]. Furthermore, there is evidence in the manufacturing domain that proves the
applicability of ontologies for modeling complex information [NFG+16]. However,
there is no universal and seamless method for developing ontologies that address the
specific characteristics of complex information models in the engineering of CESs and
the different domains that CESs are applied to. The contribution of this paper is
threefold: First, we analyzed industry requirements elicited within the research project
CrESt2 (Collaborative Embedded Systems), in order to identify different applications of
ontologies in the engineering of CESs, and to extract requirements for the development
of respective ontologies (Section 2). Second, a first approach towards a seamless method
for ontology building in the engineering of CES is proposed (Section 3). Third, the first
methodological building block of this method, the ontology requirements specification
(ORS), is discussed in detail (Section 4). Section 5 contains a summary and an outlook
to conclude the paper.


2        Requirements and Related Work regarding Ontologies in the
         Development of Collaborative Embedded Systems
This section presents the results of an analysis of industry requirements on information
models and methods for their development, as well as desired applications of
information models in the context of CES. Furthermore, requirements concerning
methods for ontology building that have been extracted from industry requirements are
presented.
Industrial Requirements and Applications
In CrESt, a total3 of 22 requirements regarding models and 16 requirements regarding
methods have been collected by industry partners with respect to the context of CES in
the Use Cases “Flexible and Adaptable Factory (UCF) and “Distributed Energy
Production” (UCE). In the first step, these requirements regarding the models have been
analyzed in comparison in order to identify commonalities. The result of this analysis are
keywords that have been used for creating a classification of requirements. We identified
2
    See https://crest.in.tum.de
3
    Not including sub-requirements
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three categories that are labeled with the key words: (1) “Semi-formal” or “meta model”;
(2) “Simulation” or “Executable”; (3) “Machine readable” or “data model”. The results
are shown in Table 1. These key words cover all requirements for UCF and 75% of the
requirements of UCE. The extracted common requirements, represented by the three
categories, can therefore be assumed to be valid for both domains. Even though the
content of the underlying requirements in the requirement classes is heterogeneous, there
is a common need for information models in the requirements, which can be addressed
by an ontology.
               Table 1: Key-word analysis of requirements in the two use cases
 Use Case                     “Semi-formal”     “Simulation”       or   “Machine readable”
                              model             “Executable” model      or “data” model

 Distributed Energy (UCE)     2 out of 4        -                       1 out of 4

 Adaptable Factory (UCF)      4 out of 18       10 out of 18            4 out of 18


In the second step, the commonalities have been analyzed to address the common needs.
This analysis of the requirement categories has shown three possible applications of
ontologies: (A1) Ontologies for the creation of profiles that can be used for the semi-
formal modelling of context. In this application of an ontology, an existing meta model
of the Object Management Group is extended by using a domain specific vocabulary that
is modelled with UML (Unified Modelling Language) class diagrams. A process
description for extending the meta model is described in [TBW13] and [FV04]. (A2)
Ontologies for being used to represent contextual situations for the purpose of simulating
the behaviour of a CES in different contextual situations. The importance of knowledge
representation has already been identified in the in the simulation community. In [TU14]
for instance, ontologies are used for the description of properties of a factory’s objects,
which can be used for simulation of process plans. In [DÖ16], an ontology for
representing artefacts in simulation systems engineering is proposed. (A3) Ontologies
for the purpose of information provision at run-time for, or between, context-aware
applications like scheduling of manufacturing operations under changing contextual
conditions. Applications using ontologies for this purpose can be found in [WDY+17].
In [AVH16], a context-aware maintenance system is proposed that uses an ontology for
representing the shared knowledge between systems and in [PLM13] and [HLC14]
ontologies are used for providing the necessary information for orchestrating
manufacturing services. However, the requirements that ontologies have to fulfil in these
different applications (A1 – A3) are not identical. In Ontology Engineering one can
distinguish between lightweight (e.g. UML class diagrams) and heavyweight (e.g. OWL
Description Logics) ontologies [GFC04]. Applications such as (A1) require lightweight
ontologies, whereas applications such as (A2) and (A3) call for heavyweight ontologies
that provide a higher degree of formalism than lightweight ontologies do. Regarding the
methods concerning the modelling of context, 5 out of 12 (UCF) and 3 out of 4 (UCE)
requirements concern the creation of models, which leads to the building of
60 Constantin Hildebrandt, Sebastian Törsleff, Torsten Bandyszak, Birte Caesar,
Alexander Ludewig,
4 C. Hildebrandt,    Alexander
                  S. Törsleff,    Fay
                               T. Bandyszak, B. Caesar, A. Ludewig, A. Fay

aforementioned ontologies. Due to the different applications (A1-A3) of ontologies in
the field of CESs and also the amount of different models required by industry, a
universal method for building ontologies in the domain of CES is to be preferred at the
moment, instead of ad-hoc building application-specific ontologies for both, scientific
community and industry partners. To summarize, two statements can be made based on
the aforementioned analysis. First, ontologies are necessary for solving the upcoming
challenges in designing CESs since they at least help addressing most model-related
requirements. Second, a method is needed for the creation of these ontologies that can be
applied in the development process of CES. Even though several approaches with
respect to ontology building have been proposed, e.g. METHONTOLOGY [FGJ97],
DILIGENT [PST04], On-To-Knowledge [SSS+01], NeOn Methodology [SGM+12] and
UPON [NMN09], none of them fulfils all of the requirements regarding ontology
building, which are listed below. Therefore, a method has been developed that addresses
the requirements regarding context modelling and the related methods; this method is
briefly introduced in section 3.
Requirements regarding Ontology Building
Additional requirements with respect to ontology building have been extracted from the
industry requirements and are discussed subsequently. The method presented in section 3
has to fulfil the following, ontology building-specific requirements: (R1) Iterative
procedure: Information models in the engineering domain can become very complex.
The Standard for the Exchange of Product Model Data (STEP) can be taken as an
example here. The STEP standard consists of 55 sub standards [ISO 10303-1] that define
how the data of a product during its life cycle can be modelled. For the purpose of
bringing this information into an ontological structure, an iterative procedure is
necessary such that the resulting ontology caters the actual needs of an engineering
project. (R2) Modularization of knowledge: Since the information in the different
domains of CESs is very complex, the methodology should explicitly support the
modularization of the domain´s knowledge in order to support the reuse of existing
ontologies and also allow for application-specific parts of the ontology instead of
providing the full amount of knowledge in one model. (R3) Different solution paths:
The different addressed applications have different starting points for ontology creation.
For some of the information necessary in the UCF for instance, ontologies are readily
available (e.g. ontology design patterns 4 or complete ontologies). On the other hand, an
ontology that specifically addresses the context of collaborative embedded systems
would have to be created from scratch. (R4) Applicable for lightweight and
heavyweight ontology building: For the development of CESs there are different levels
of formalism necessary. In order to create a profile for instance, the formalism necessary
can be modelled with a class diagram. For applications involving simulations, however,
logically interpretable ontologies are required, for instance description logics. Thus, the
method shall support different levels of formalism. (R5) Seamless creation of light and
heavyweight ontologies: Since a lightweight ontology already contains some of the
information necessary for a heavyweight ontology, the method should support the
4
    For instance: http://ontologydesignpatterns.org/wiki/Submissions:MaterialsProperty
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seamless development of ontologies from ontological requirements via lightweight
ontologies to heavyweight ontologies. (R6) Reuse of existing ontologies: the reuse of
ontologies should be supported in a structured manner. (R7) Reuse of non-ontological
resources: For most information to be modelled, there already exists an enormous
amount of information resources (e.g. national & international standards, company-
specific process description, classification systems like ecl@ss etc.). The method for the
creation of an ontology has to allow the structured use of such information pools. (R8)
Integration into the engineering workflow: Since ontology building is a process that
will be performed in addition to the engineering of CES, it is necessary that the
interdependencies with the engineering workflow are explicitly considered.


3    An Initial Method for Ontology Building for Collaborative
     Embedded Systems
Based on the elicited industry requirements and the discussion in section 2, a method has
been developed that addresses the discussed requirements. The method is divided into
multiple MBBs as it has been proposed in [DBB+16]. Note, that a detailed explanation
of every building block is out of scope of this paper (see section 5) and instead subject of
future contributions. The method is shown in Fig. 1, while the satisfaction of R1-R8 is
subsequently discussed. The method distinguishes between two types of artefacts: pre-
existing artefacts that can be reused in engineering projects (shown in blue in Fig. 1) and




       Fig. 1: Initial method for Ontology Building for Collaborative Embedded Systems
62 Constantin Hildebrandt, Sebastian Törsleff, Torsten Bandyszak, Birte Caesar,
Alexander Ludewig,
6 C. Hildebrandt,    Alexander
                  S. Törsleff,    Fay
                               T. Bandyszak, B. Caesar, A. Ludewig, A. Fay

project-specific artefacts (shown in green in Fig. 1). Furthermore, we distinguish
between informal, semi-formal and formal artefacts. The ontological building process
consists of MBBs that can be used, if required by project requirements, and consist of
tasks that can be performed iteratively (see also section 4). In the first MBB, the
ontology requirements are extracted from the project requirements. The second MBB
uses these ontological requirements to build a lightweight ontology that can be used to
create domain-specific profiles in order to extend existing metamodels or profiles
[TBW13]. Such semi-formal context models (see [DTW12] for a detailed introduction to
context models) can be modelled using UML or SysML. This MBB also considers
existing artefacts of ontological and non-ontological nature. The third MBB uses the
project-specific artefacts created so far (at least the ORS Document) and builds a formal
ontology that can be used to formalize the semi-formal context models, which allows
reasoning during runtime as well as simulation based on formal context models. The use
of MBBs satisfies the requirements R2, R3 and R8. The requirements R6 and R7 are
satisfied by explicit consideration of external resources. The requirements R4 and R5 are
also considered by using directly related MBB for R4 as well as by the definition of an
interface to lightweight ontologies in heavyweight ontology building (R5).


4        Ontology Requirements                        Specification           for      Collaborative
         Embedded Systems
In this section, the first MBB of the method proposed in section 3 is described. For the
purpose of (ORS), the NeOn Methodology is chosen, since this method, compared to all
above mentioned approaches, covers most of the requirements stated in section 2. The
requirements R4, R5 and R8 are not covered, neither by the NeOn Methodology nor by
any other approach listed above. This can be traced back to the different scope of the
approaches which focus on heavyweight ontology development in the Semantic Web
domain. The process of ORS according to [SGV09], which is part of the NeOn
methodology, is shown in Fig. 2. The remainder of this section applies this approach to
the domain of CES. The ORS process consists of eight tasks (see Fig. 2). However, a
focus is set on tasks 1, 3 and 4, since they differ in the domain of CES from the Semantic
Web domain and the method in [SGV09]. The example use case in the following is the
creation of a profile according to [TBW13] for the purpose of defining a domain specific
language for UCF. The documentation of the ORS can be done in a tabular format, while
a template, can be accessed online5. The stakeholders involved in the ORS are domain
experts, ontology specialists and users of the ontology. Most ORS tasks are performed
jointly by all stakeholders, except for task 6 (only users and domain experts) and task 8
(only ontology specialists). The input of the ORS is a set of ontological needs. The
output is a document stating all requirements that the ontology has to fulfil and that the
ontology is verified against after it has been developed. In task 1, the objective is to
define the purpose, scope and implementation language of the ontology. To this end, the
5
    Online link to the ORS document template: https://www.hsu-hh.de/aut/forschung/forschungsthemen/crest-
    modellbasierte-entwicklung-kollaborativer-eingebetteter-systeme
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ontology specialists interview the domain experts and users. In case the goal is the
creation of a profile, the interview would yield that the ontology purpose is the definition
of stereotypes (classes and relations), tagged values and constraints (see [FV04]) that can
be used for implementing a profile. The scope addresses granularity and domain
coverage of the ontology. In the context of CES, the scope might refer to upper
ontologies or domain ontologies. While upper ontologies consist of concepts that are
abstract and address different domains, a domain ontology is limited to concepts that are
specific to a certain domain, e.g. UCF [AZW06].
                     Task 1: Identify
                   purpose, scope and      Task 2: Identify          Task 3: Identify          Task 4: Identify
      Start
                    implementation       intended end users           intended uses             requirements
                       languages


                                             Ontology
                        Project                                                                Task 5: Group
                                           Requirements
                     requirements
                                            Document                                    No     requirements




                     Task 8: Extract
                                          Task 7: Prioritize         Requirements            Task 6: Validate set
      End          terminology and its
                                           requirements        Yes      valid?                of requirements
                       frequency



Fig. 2: Tasks to be performed for ORS, based on [SGV09]
An exemplary upper ontology would be an ontology that comprises concepts and
relations for UCF and UCE in a generic CES ontology. Domain ontologies on the other
hand can consist of even more specific subdomains. In a domain ontology for the UCF
for instance, one may define “mechanical engineering” as a more detailed domain (i.e.
subdomain), or even “mechanical cylinder construction” as a subdomain of “mechanical
engineering”. In our running example, the domain is defined as “Manufacturing Order
Processing”. Suitable implementation languages have to be identified with respect to the
ontology purpose. In the case of profile creation, SysML can be chosen in order to
represent the stereotypes and relations, while OCL (Object Constraint Language) is
chosen for the definition of the constraints. In task 2, the intended end users of the
ontology are identified. For the running example, two intended user roles can be
identified, i.e. a model based systems (MBS) engineer who performs the profile creation
and a MBS engineer that uses the profile. Task 3 is concerned with specifying the
intended uses of the formerly identified users. This is achieved by the definition of
scenarios in which the ontology has to provide information for the purposes defined in
task 1. Which procedure to use for information gathering is dependent on whether the
information regarding the intended use is implicit or explicit (e.g. any pre-existing
document specifying the intended uses is available) knowledge of a user or domain
expert. In case the information is explicit, interviews are appropriate to gather the
required information sources. In contrast, if the information is implicit, a workshop
employing creative techniques (e.g. gallery method or method 635 [PBB+07]) should be
held in order to identify as much scenarios as possible. A model-based documentation of
64 Constantin Hildebrandt, Sebastian Törsleff, Torsten Bandyszak, Birte Caesar,
Alexander Ludewig,
8 C. Hildebrandt,    Alexander
                  S. Törsleff,    Fay
                               T. Bandyszak, B. Caesar, A. Ludewig, A. Fay

the intended uses is recommended, since it facilitates the subsequent tasks. For the
running example it is assumed that the users were not able to write down the intended
uses or refer to any document stating the intended use, as they are not yet aware of how
the target SysML profile extension will be applied in the end. Therefore, the intended
use can be seen as implicit knowledge and a workshop with creative techniques has to be
performed. In this workshop, the users and domain experts create SysML diagrams of
possible application scenarios of the profile in small working groups. An example
diagram is shown on the left side of Fig. 3, where the SysML block definition diagram is
used without the profile to be developed in order to address possible applications of the
profile. As a result, model elements that require the definition of ontological concepts
are highlighted in the diagram. These potential applications are called “Point of Interest”
(POI). For every POI in a diagram the stakeholders will define requirements in task 4.
These POIs are the definition of the intended use and the result of task 3.




Fig. 3: Example results of task 3 and task 4
After having defined the intended uses, in task 4 the technical and constraining
requirements are extracted from the results of the former tasks. Technical requirements
are formulated as so called competency questions (CQs), which the ontology has to
provide answers to, i.e. knowledge that the ontology has to cover. These CQs can be
extracted from the results of task 3. This is achieved through the definition of a CQ for
each POI, which we exemplify on the right side of Fig. 3. In case the domain experts and
users can already provide answers to the questions, these are documented as well. In
contrast, CQs that cannot be answered due to implicit knowledge of experts and users, or
due to missing information, are tagged in the ORS document to highlight the need for
further investigation. The CQs and their corresponding answers are the essential
requirements used later on within the process of building a light- or heavyweight
ontology in order to verify whether the ontology captures all necessary concepts. In
addition to the CQs, constraining requirements include general aspects like
“Consideration of standard ISO 10303 for product models” or characteristics like
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multilingualism. In task 5, the gathered CQs and answers are grouped according to a set
of different criteria by domain experts, users and the ontology specialists. These groups
can be content-specific, like used measures or referenced objects (to be defined by users
and domain experts) or scope-related. The scope related groups should comprise
“UpperOntology”, “DomainOntology” and “SubDomainOntology”. In task 6, the users
and domain experts perform a validation of the gathered requirements using a checklist
(see online template). This checklist contains questions that the domain experts and users
have to answer positively, in order for the requirements to be valid. This aims to ensure
that the requirements are complete, consistent, verifiable, understandable, unambiguous,
concise and modifiable. Upon validation, the requirements are prioritized in task 7. This
is especially important if the set of requirements is large or some requirements’
implementation has to precede others. This task is performed by interviews in which the
ontology specialists interview the domain experts and users. Task 8 concerns the
extraction of terms and their frequency from the CQs and their respective answers in
order to build a pre-glossary of terms. This pre-glossary is divided into three parts. The
first part identifies terms and frequency based on the CQs, the second one is based on the
related answers, and the third part identifies objects that can be seen as instances of other
classes.


5    Summary and Outlook
This paper has shown the need for a seamless method for ontology building in the
domain of Collaborative Embedded Systems (CES) by collecting requirements on
information models proposed by industry, and by introducing possible applications of
those information models as required by industry. Furthermore, an initial method has
been proposed, which aims to fulfil these requirements by defining a generic process that
distinguishes lightweight and heavyweight ontologies, and accounts for different
artefacts as well as the potential applications of ontologies. Furthermore, we introduced
the first MBB of this method. Our future research will focus on light- and heavyweight
ontology building for CES to address the stated requirements. Furthermore, we will
analyse the application of ontologies to CES relevant topics, e.g. system variability and
open contexts.


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