=Paper=
{{Paper
|id=Vol-2835/paper2
|storemode=property
|title=Ontological Foundations for Trust Management: Extending the Reference Ontology of Trust
|pdfUrl=https://ceur-ws.org/Vol-2835/paper2.pdf
|volume=Vol-2835
|authors=Glenda Amaral,Tiago Prince Sales,Giancarlo Guizzardi,,Daniele Porello
|dblpUrl=https://dblp.org/rec/conf/vmbo/AmaralSGP21
}}
==Ontological Foundations for Trust Management: Extending the Reference Ontology of Trust==
https://ceur-ws.org/Vol-2835/paper2.pdf
Ontological Foundations for Trust Management:
Extending the Reference Ontology of Trust
Glenda Amaral1 , Tiago Prince Sales1 , Giancarlo Guizzardi1,2 , and Daniele Porello3
1
Conceptual and Cognitive Modeling Research Group (CORE),
Free University of Bozen-Bolzano, Bolzano, Italy
{gmouraamaral, tiago.princesales, giancarlo.guizzardi}@unibz.it
2 Services & Cybersecurity, University of Twente, The Netherlands
3 ISTC-CNR Laboratory for Applied Ontology, Trento, Italy
daniele.porello@loa.istc.cnr.it
Abstract. In this paper, we provide a semantic foundation for trust-related con-
cepts in the light of trust management. We extend our previous work, the Refer-
ence Ontology of Trust, to clarify and provide a deeper account of some building
blocks of trust, such as beliefs and intentions of a trustor, pieces of evidence that
indicate that a trustee is trustworthy (or not), as well as the many factors that in-
fluence trust. We illustrate our proposal by instantiating and discussing people’s
trust in vaccines in the time of COVID-19.
Keywords: Trust Management · Ontological Analysis · OntoUML.
1 Introduction
Trust is about relationships. It is about accepting to be vulnerable to the behavior of
others in order to achieve our objectives. A trust relation requires two entities, and can
therefore be seen from their two perspectives. The relying agent, the trustor, is inter-
ested in assessing the trustworthiness of a trustee, as correctly as possible. The trustee
is interested in identifying what makes it trustworthy, possibly identifying what it could
change to increase trust levels, as well as the key capabilities it needs to guarantee well-
placed trust. From the trustee’s perspective, as important as gaining trust is having the
ability to maintain it. Trust may break in an instant or erode gradually. Therefore, it is
important to build sustainable trust that cannot be easily lost. But how can one manage
trust? What makes one trustworthy? And what factors can influence trust? Although a
proper conceptualization is fundamental to efficiently manage trust, there is no consen-
sus on a definition of trust in literature [28,33].
In a previous effort [4], we proposed the Reference Ontology of Trust, an ontolog-
ically well-grounded reference model that formally characterizes the concept of trust,
as well as clarifies the relation between trust and risk, and represents how risk emerges
from trust relations. This paper sheds new light on trust-related concepts and relations
under the perspective of trust management [18,29]. We extend our previous work to
clarify and provide a deeper account of (i) the factors that influence trust, (ii) the com-
plexity of the intentions of a trustor (iii) the pieces of evidence that indicate that a trustee
is trustworthy (or not), and (iv) the quantitative perspective of trust.
G. Amaral et al.
The remainder of this paper is organized as follows. In Section 2, we introduce the
reader to the Reference Ontology of Trust. Then, in Section 3 we present our proposal
for extending this ontology. In Section 4, to demonstrate the contribution of our proposal
to the modeling practice, we apply it to model an example about vaccines in the time of
COVID-19. We conclude the paper in Section 5 with some final considerations.
2 The Reference Ontology of Trust (ROT)
The Reference Ontology of Trust1 (ROT) is a reference model, grounded on the Unified
Foundational Ontology (UFO) [11,13], that formally characterizes the concept of trust
and represents how risk emerges from trust relations [4]. Some of its main ontological
commitments on the nature of trust are listed below:
– Trust is relative to intentions [5]. An agent, the trustor, trusts an individual, the
trustee, only relative to a certain intention, for the achievement of which she counts
upon it.
– Trust is grounded on beliefs [5]. If we trust an individual, we believe that it can
do certain things, that its environment will not prevent it from doing them, and, if
it has agency, that it wants to do those things.
– Trust can be quantified [6]. Our trust in a certain individual can increase or de-
crease in time, and we can trust certain individuals more than others. To account
for these scenarios, ROT assumes that trust can be quantified, even if it does not
commit to any particular scale or measurement strategy.
– A trustee does not need agency [5]. The necessary condition for a trustee is that it
is an entity capable of having a (hopefully positive) impact on our intentions by the
outcome of its behavior. Thus, a trustee may be an agent (e.g. a person, an animal,
an organization) or an object (e.g. a car, a vaccine)
Figure 12 depicts a ROT excerpt, which is represented in OntoUML, an ontology-
driven conceptual modeling language based in the Unified Foundational Ontology [11].
In ROT, Trust is modelled as a complex mode (an externally dependent entity, which
can only exist by inhering in other individuals [11]) composed of an Intention and a
set of Beliefs that inhere in the Trustor and are externally dependent on the Trustee
and on Dispositions [14] that are expected to inhere in the Trustee. These beliefs
include: (i) Capability Belief: a Belief that a Trustee has a Capability re-
quired to exhibit a certain behavior; and (ii) Vulnerability Belief: a Belief that
the Trustee’s Vulnerabilities will not prevent her from exhibiting a desired be-
havior. When the role of Trustee is played by an Agent, Trust is also composed
of Intention Beliefs, namely a Trustor’s belief that an Agent Trustee has an
Intention to perform the desired action.
1 The complete version of ROT in OntoUML and its implementation in OWL are available at
http://purl.org/krdb-core/trust-ontology.
2 We adopt the following color coding in the OntoUML diagrams: substantials are represented
in pink, qualities in blue, relators and extrinsic-modes in green, events in yellow, and classes
whose instances might be of different ontological nature in gray.
Ontological Foundations for Trust Management
Fig. 1: The Reference Ontology of Trust
3 Extending the Reference Ontology of Trust
3.1 Detailing Intentions
Trust is always about an intention of the trustor, for the achievement of which she counts
upon the trustee. Such an intention is not always atomic. For instance, consider the fol-
lowing trust relation “Mary trusts her doctor to diagnose a disease she may have”. In
this case, trust is about an atomic intention of the trustor, namely “having a disease di-
agnosed”. Differently, in the trust relation “Bob trusts a certain airline to take him on his
holiday trip comfortably and safely”, trust is about a complex intention, composed of
(i) Bob’s intention of traveling; (ii) his intention of being safe; and (ii) his intention of
being comfortable. Let us now consider a situation in which Mary trusts an application
provider for collecting her location data, except when she is in sensitive places such as
a cancer treatment center for her medical treatment, since such information may lead
to disclosing her disease. In this example, trust is also about a complex intention, com-
posed of (i) Mary’s intention of having her location data collected; (ii) Mary’s intention
of not having her diseased disclosed to others; and (iii) Mary’s intention of preserving
her location privacy when she is in sensitive places.
We have extended the Reference Ontology of Trust to support the representation
of complex intentions. As depicted in Figure 2, Trust is related to an intention of the
Trustor, which can be atomic or complex. While atomic intentions have no proper
parts, complex intentions are aggregations of at least two disjoint intentions.
3.2 Quantifying Beliefs
According to ROT, trust is a complex mental state of a trustor regarding a trustee and
her behavior, which is composed of an intention of the trustor and a set of her beliefs
about dispositions that inhere in the trustee. In general, a trustor’s beliefs on a trustee’s
dispositions are not black and white, in the sense that a trustor needs to believe that a
trustee either has a certain disposition or not. In fact, they have an intrinsic quality that
G. Amaral et al.
Fig. 2: ROT - Intention and Belief extensions
corresponds to the strength of a trustor’s belief [16]. For instance, it may be the case that
“Alice believes more strongly that Burger King is capable of making a good hamburger
than it is capable of delivering orders on time”. Another example, which considers the
same capability and different trustees, is “people believe more strongly that an adult
is capable of lifting a heavy object than a child”. Note that in this case, we are not
comparing the performance of an adult with that of a child when lifting a heavy object,
because the child may not even be able to lift it. Nevertheless, performance levels are
an important aspect to be considered with respect to capability beliefs. For example,
a project manager may believe that both a junior and a senior analysts are capable of
performing a particular task. However, he probably believes that the senior analyst is
able to perform the task with a higher level of performance than the junior analyst. In [5]
Castelfranchi and Falcone claim that the degree of trust is a function of (i) the estimated
quantitative level of the trustee’s quality on which the positive expectation is based and
(ii) how much the trustor is sure of her evaluation about the trustee’s quality. In our
approach, the belief intensity and the performance level are analogous to, respectively,
(ii) and (i) in Castelfranchi and Falcone’s proposal [5].
Finally, another important aspect to be considered, related to beliefs about trustee’s
dispositions, is how strongly the trustor believes a disposition may be manifested through
the occurrence of certain events. For example: “although Charlie believes that he can
get a flat tire during a trip (which corresponds to a vulnerability belief about his car), he
believes that the likelihood of this happening is very small”.
Note that the very same disposition may play the role of a capability, a vulnerability,
or even a threat capability3 . For example, in the scope of military operations, informa-
tion can be seen both as a capability (as digital data and networks support and facilitate
the achievement of military objectives) and a vulnerability (as confidential information
can be disclosed as a consequence of a cyber-attack). For this reason, both capabilities
and vulnerabilities are represented as roles of dispositions (Figure 1).
Based on these considerations, we propose that the above-mentioned measures (be-
lief intensity, performance level, and manifestation likelihood) be considered when
quantifying trust. To account for this quantitative perspective of disposition beliefs, we
3 Capabilities are usually perceived as beneficial, as they enable the manifestation of events
desired by an agent. However, when the manifestation of a capability enables undesired events
that threaten an agent’s abilities to achieve a goal, it can be seen as a threat capability [30].
Ontological Foundations for Trust Management
have extended ROT to include these three belief-related measures (Figure 2), represent-
ing them as qualities4 that inhere in aspectual (belief intensity) and disposition beliefs
(performance level and manifestation likelihood). This means that they can be mapped
into quality spaces, such as a discrete scale like or a continuous
one like <0-100> [1,7,19].
3.3 Dispositional Evidence
It is generally accepted in the literature that by trusting, the trustor accepts to become
vulnerable to the trustee, based on the expectation that the latter will perform a particu-
lar action or exhibit a particular behavior important to the trustor [20,28,5]. Therefore,
it is probably that the trustor only decides to make herself vulnerable if she has reasons
to believe that the trustee is trustworthy.
Riegelsberger et al. [27] discuss the importance of signaling the existence of trust-
warranting properties and providing evidence of trustworthy behavior of the trustee. In
a previous work [2], we have proposed the modeling of trust-warranting signals that
should be emitted by the trustee in order to ensure trustworthy behavior and promote
well-placed trust. In this paper, we leverage this analysis to explore a broader view on
the factors that indicate that the trustee is capable of successfully realizing the capabil-
ities and prevent the manifestation of the vulnerabilities, which we name here disposi-
tional evidence (in line with Vinkovits et al. [32]). Examples of dispositional evidences
are certifications by trusted third parties (e.g. Mary has a TOEFL certification. This
makes me believe that she can speak English, because I trust the certificate issuing au-
thority); trustee’s credentials (degrees, accreditations, awards) that suggests the trustee
is doing a good job and the like; history of performance (e.g. number of accurate di-
agnosis issued by a medical diagnosis system); information on the trustee track record
(such as reviews from service recipients and statistics on its experience); recommen-
dations (e.g. my brother trusts a car mechanic and recommends his services to me);
reputation records (e.g. the number of positive evaluations received by an Uber driver);
reliability (e.g. a doctor who has a history of delivering reliable healthcare services to
its patients); availability (e.g. a medical doctor you rarely succeed to make an appoint-
ment with is not trustworthy); past successful experiences (e.g. for all the purchases I
made at Amazon the products arrived on time and in perfect conditions); transparency
(e.g. offering information on what a software system is doing, as well as rationale for its
decisions (aka explainability)); longevity (e.g. indications that a vendor has been in the
market for a long time and that it is interested in continued business relationship with
the client); presence of risk mitigation measures (which indicates that measures have
been taken in order to prevent the manifestation of the vulnerabilities), among others.
Ontologically speaking, Dispositional Evidences are social entities, typically
social relators (e.g. a relator binding the certifying entity, the certified entity and refer-
ring to a capability, vulnerability, etc.), but also documents (social objects themselves)
4 In UFO, a quality is an objectification of a property that can be directly evaluated (projected)
into certain value spaces [11]. Common examples include a person’s weight, which can be
measured in kilograms or pounds, and the color of a flower, which can be specified in the RGB
or HSV color models.
G. Amaral et al.
that represent these social entities (e.g., in the way a marriage certificate documents
a marriage as a social relator). As illustrated in Figure 3 we extended ROT to model
Dispositional Evidences as roles played by endurants (objects, relators, etc.) re-
lated to a Disposition of a Trustee.
Fig. 3: ROT - Trustworthiness Evidence and Influence Extensions
3.4 The Role of Influences
We previously mentioned that trust is composed of a trustor’s intention and a set of her
beliefs about the trustee and her behavior. However, several other factors that influence
the formation of trust are often discussed in the literature. For instance, Mayer et al.
[20] present a review of factors that lead to trust, while Castelfranchi and Falcone [5]
argue that “trust changes with experience, with the modification of the different sources
it is based on, with the emotional or rational state of the trustor, with the modification
of the environment in which the trustee is supposed to perform, and so on”. According
to them, as trust depends on dynamic phenomena, it is itself a dynamic entity. Here, we
rely on the ontological nature of the sources of influence to propose a set of categories to
classify the many factors that can affect a trustor’s beliefs about a trustee’s dispositions
and, consequently, influence trust. We distinguish the sources of influence between (i)
other trust relationships, (ii) mental moments, and (iii) dispositional evidence, explained
as follows.
Trust Influence. This category represents the situation in which trust is influenced by
the existence of another trust relationship. According to Castelfranchi and Falconi [5]
“in the same situation trust is influenced by trust in several rather complex ways”. In [8]
the authors also discuss “how trust creates a reciprocal trust” and “how A’s trusting B
can influence C trusting B or D, and so on”. In fact, countless examples can be found in
real life about trust influencing trust, either positively or negatively. In a previous paper,
[3] we discussed the case of a recent study published in The Lancet journal [24], which
relied on data gathered by a US healthcare analytics company to report issues on the
efficacy and safety of hydroxychloroquine for treating COVID-19. When the study was
Ontological Foundations for Trust Management
first published, it prompted the WHO along with several countries to pause trials on
this drug. However, this very study was retracted [25] a few days later (and the clinical
trials resumed), as concerns were raised with respect to the veracity of the data. In this
example, we have that: as (1) “WHO trusts The Lancet” and (2) “The Lancet trusts the
Publication Authors”, consequently, to some extent (3) “WHO trusts the Publication
Authors”, and in this case both (1) and (2) positively influences (3). In [17] Josang et
al. mention examples of trust influence observed among animals: “when bees signal
to each other where to find pollen, the other bees can derive trust in a specific pollen
harvesting area; when animals give warnings about danger, it can be interpreted as a
recommendation about distrust, as in the case of a presence of potential predator”.
Mental Moment Influence. This category represents situations in which trust is in-
fluenced by mental moments (a concept from UFO). In UFO, agents can bear special
types of modes (aspects, features, characteristics, objectified properties) named intrin-
sic moments. Mental moment is a special type of intrinsic moment that is existentially
dependent on a particular agent, being an inseparable part of its mental state (Figure 1).
Examples of mental moments include perceptions, beliefs, desires and intentions (in-
ternal commitments). Perception is a relevant concept to express the relation of agents
to events sensed from the environment and from other agents [15]. Belief regards infor-
mation the agent has about the environment and about other agents. The propositional
content of a belief is what an agent holds as true (e.g., one’s belief that Earth orbits
around the Sun). Desires and intentions can be fulfilled or frustrated. A desire expresses
the will of an agent towards a possible situation (e.g., a desire that Italy wins the next
World Cup), while an intention expresses desired states of affairs for which the agent
commits to pursuing (e.g., Mary’s intention of going to Paris to see the Eiffel Tower).
For an extensive discussion of mental moments, please refer to [12].
Mental moments can play an important role in influencing trust. Let us consider
the example of a person who desires to travel on the next summer break and receives
an email containing an amazing offer for an exceptional and hard to refuse destination
that expires in a short period of time which she can’t miss. Although it might look
like a travel scam, the person’s desire to travel may influence her to trust the email of-
fer. Internal commitments may also influence one’s trust. For instance, people strongly
committed to environmental preservation tend to trust companies that support envi-
ronmental sustainability. There is also the case of trustor’s beliefs, not related to the
trustee’s dispositions, which can influence trust. Examples are some religious beliefs,
which prescribe honesty and mutual love [21], leading people to assume general others
are usually honest, benevolent, competent, and predictable [22].
Another important aspect is the occurrence of events that can affect the trustor’s per-
ception regarding a particular trustee. In [23] McKnight et al. discuss how trust changes
in response to external events and propose a model that addresses the mental mecha-
nisms people use as they are confronted by trust-related events, which “indicates that
trust may be sticky or resistant to change, but that change can and will occur” [23].
According to Castelfranchi and Falconi [9], the success of an action performed by the
trustee in order to reach a goal of the trustor depends not only on the trustee’s capa-
bilities but also on external conditions that allow or inhibit the realization of the task.
To illustrate this, the authors mention the case of a violinist that has to do the concert
G. Amaral et al.
in an open environment and the weather conditions are particularly bad (very cold). In
general, people trust the violinist to play a good performance, but their trust level may
decrease due to the bad weather, as people may infer that these conditions can modify
his specific hand abilities and his performance. Similarly, in financial systems, the ar-
rival of bad news about a financial agent can lead others to lose confidence in it, which
in turn can spread across the entire system.
Dispositional Evidence Influence. This category represents the situation in which trust
is influenced by dispositional evidences. As aforementioned, dispositional evidences
are related to dispositions of the trustee, such as certificates, history of performance,
recommendations, reputation records, past successful experiences, among others, which
can influence the trustor’s beliefs about the trustee and, consequently, influence trust.
As illustrated in Figure 3, in order to represent the role of influences, we extended
ROT to include the Influence relator, which connects the sources of influence to the
disposition beliefs of the trustor under their influence. We distinguish Influence ac-
cording to the source of influence into: (i) Trust Influence, associated to a Trust re-
lationship; (ii) Mental Moment Influence, associated to a Mental Moment; and (iii)
Dispositional Evidence Influence, associated to a Dispositional Evidence.
The property weight corresponds to the weight of an influence over a particular belief,
as certain influences may weight more heavily than others.
4 The Case of Vaccines in the Time of COVID-19
According to the World Health Organization (WHO), there are currently more than
50 COVID-19 vaccine candidates in trials [34]. Naturally, each of them may present
differences when it comes to efficacy. A study found that Pfizer-BioNTech vaccine
efficacy was 52% after the first dose and 95% after the second [26]. This stands for
a dispositional evidence that can positively influence people’s trust in the
vaccine (a dispositional evidence influence), as it can lead people to believe
that Pfizer-BioNTech vaccine is capable of protecting from COVID-19 (capability
belief) with a high performance level. Let us suppose that another study shows
that the efficacy of a second candidate is lower. This is a dispositional evidence
that may lead people to believe that the performance level of the second candi-
date’s capability of protecting from COVID-19 is lower than Pfizer-BioNTech’s. Con-
sequently people’s trust degree will be higher in their trust relationship with Pfizer
than in their trust relationship with the second candidate. Considering that Pfizer and
BioNTech are, respectively, from the USA and Germany, it is possible that citizens of
these two countries have more trust in the Pfizer-BioNTech vaccine than in the ones
produced by pharmaceutical companies from other countries. That is because peo-
ple’s trust in the science and technology capacity of a particular country positively
influences their trust in the pharmaceutical companies from that country (a trust
influence).
Now let us consider the case of two friends, Tom and Jerry (trustors), who trust
Pfizer-BioNTech COVID-19 vaccine (trustee) with different trust degrees. They
trust the vaccine to safely protect them from COVID-19. Note that their trust is about a
complex intention, composed of (i) the intention of being protected from getting
Ontological Foundations for Trust Management
COVID-19; and (ii) the intention of not experiencing side effects from the vaccine.
Tom does not have any health issues. He strongly believes (belief intensity) that
the vaccine can protect him from COVID-19 (a capability belief) and that its side
effects (a threat capability) will not harm him (a capability belief). Jerry is
allergic. His trust degree in the vaccine is lower than Tom’s, as he believes that there
is a small likelihood (manifestation likelihood) that the side effects (a threat
capability) will harm him (a capability belief). Unfortunately, Jerry saw on
the news that three Alaska health care workers had an allergic reaction after receiving
a dose of the new Pfizer COVID-19 vaccine [10]. His perception about this event
negatively influenced his trust in the vaccine (a mental moment influence), as
he started to believe that there is a high likelihood (manifestation likelihood)
that the vaccine side effects will harm him. Conversely, people been vaccinated around
the world and reporting just mild side effects are events that can be perceived by peo-
ple in a positive way and consequently, positively influence people’s trust in the
vaccine (a mental moment influence). Hopefully, in Jerry’s case, the influence
weight of “people having just mild side effects” will be higher than the influence
weight of the news about “the Alaska health care workers having allergic reactions”.
If we consider the case of people who opposes vaccines, their anti-vaccination beliefs
(a mental moment) negatively influence their trust in a COVID-19 vaccine (a
mental moment influence).
Finally, the US President-elect Joe Biden receiving the first dose of COVID-19 vac-
cine on live television and stating that “ I’m doing this to demonstrate that people should
be prepared when it’s available to take the vaccine” [31] is an event that can be per-
ceived by people in a positive way, thus positively influencing people’s trust in the
vaccine (a mental moment influence).
5 Final Remarks
In this paper, we conducted an ontological analysis to investigate the proper represen-
tation of the factors that influence trust as well as other trust-related concepts, such
as beliefs and intentions of a trustor and pieces of evidence that indicate a trustee’s
trustworthiness. Additionally, we provided an ontological account for the quantitative
perspective of a trustor’s beliefs. To demonstrate the applicability of our proposal, we
instantiated our ontology with an example in the context of COVID-19 vaccines. As
future work, we plan to use our ontology as a foundation for designing a modeling
framework that allows for the quantification and reasoning about trust and trustworthi-
ness.
Acknowledgments
CAPES (PhD grant 88881.173022/2018-01) and NeXON project (UNIBZ).
G. Amaral et al.
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