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This study introduces a Mitigation Ontology (MO) designed for the analysis of safety-critical systems. Recognizing the paramount importance of systematically addressing potential risks and hazards in complex systems, the proposed ontology serves as a structured framework for comprehensively modeling and analyzing mitigation strategies. Leveraging ontological principles, the framework enables a precise representation of safety-critical information, emphasizing the relationships and dependencies among various mitigation elements. To encapsulate the essence of safety-critical systems and support understanding of the mechanisms of situations, events, and associated hazards, we propose a hazard and mitigation domain ontology, i.e., the MO to provide a combined ontological interpretation of hazard and mitigation strategies. The MO facilitates a more thorough and standardized analysis of safety measures, contributing to enhanced understanding, communication, and implementation of mitigation strategies in software and hardware levels of safety-critical systems. The MO is grounded on Unified Foundational Ontology (UFO) and based on widely accepted standards, and scientific guides. We demonstrate our proposed ontology in the autonomous vehicle domain to check how it can help to analyze the safety of real-world safety-critical systems. Through the ontology instantiation process for a case study from the autonomous vehicle domain, we have verified that safety-critical related hazards, causes and consequences, and other entities contributing to hazards were well identified. we have seen that the MO offers a shared vocabulary that facilitates communication among diverse communities, preventing misunderstandings among engineers and stakeholders involved in safety-critical systems. Additionally, the conceptual model serves as a reference point for developers of safety-critical systems, enabling them to systematically extract and analyze safety requirements specifications and provide safety mechanisms.

Today, well-established hazard analysis techniques are available and widely used to identify hazards for single systems in various industries. However, hazard analysis techniques for a System of Systems (SoS) are not properly investigated. SoS is a complex system where multiple systems work together to achieve a common goal. However, the interaction between systems may lead to unforeseen interactions and interdependencies between systems. This increases the difficulty of identifying and assessing system failures and potential safety hazards. In this paper, we explore whether Hazard Ontology (HO) can be applied to an SoS and whether it can identify emergent hazards, their causes, sources, and consequences. To conduct our exploration, we apply the HO to a quarry automation site (an SoS) from the construction equipment domain. The results indicate that the HO is a promising technique that facilitates the identification of emergent hazards and their components. 

While ontology comparison and alignment have been extensively researched in the last decade, there are still some challenges to these disciplines, such as incomplete ontologies, those that cover only a portion of a domain, and differences in domain modeling due to varying viewpoints. Although the literature has compared ontological concepts from the same domain, comparisons of concepts from different domains (e.g., security and safety) remain unexplored. To compare the concepts of security and safety domains, a security ontology must first be created to bridge the gap between these domains. Therefore, this paper presents a Combined Security Ontology (CSO) based on the Unified Foundational Ontology (UFO) that could be compared to or aligned with other ontologies. This CSO includes the core ontological concepts and their respective relationships that had been extracted through a previous systematic literature review. The CSO concepts and their relationships were mapped to the UFO to get a common terminology that facilitates to bridge the gap between the security and safety domains. Since the proposed CSO is based on the UFO, it could be compared to or aligned with other ontologies from different domains.

Safety and security ontologies quickly become essential support for integrating heterogeneous knowledge from various sources. Today, there is little standardization of ontologies and almost no discussion of how to compare concepts and their relationships, establish a general approach to create relationships or model them in general. However, concepts with similar names are not semantically similar or compatible in some cases. In this case, the problem of correspondence arises among the concepts and relationships found in the ontologies. To solve this problem, a comparison between the Hazard Ontology (HO) and the Combined Security Ontology (CSO) is proposed, in which the value of equivalence between their concepts and their relationships was extracted and analyzed. Although the HO covers the concepts related to the safety domain and the CSO includes securityrelated concepts, both are based on the Unified Foundational Ontology (UFO). For this study, HO and CSO were compared, and the results were summarized in the form of comparison tables. Our main contribution involves the comparisons among the concepts in HO and CSO to identify equivalences and differences between the two. Due to the increasing number of ontologies, their mapping, merging, and alignment are primary challenges in bridging the gaps that exist between the safety and security domains. 

Security ontologies have been developed to facilitate the organization and management of security knowledge. A comparison and evaluation of how these ontologies relate to one another is challenging due to their structure, size, complexity, and level of expressiveness. Differences between ontologies can be found on both the ontological and linguistic levels, resulting in errors and inconsistencies (i.e., different concept hierarchies, types of concepts, definitions) when comparing and aligning them. Moreover, many concepts related to security ontologies have not been thoroughly explored and do not fully meet security standards. By using standards, we can ensure that concepts and definitions are unified and coherent. In this study, we address these deficiencies by reviewing existing security ontologies to identify core concepts and relationships. The primary objective of the systematic literature review is to identify core concepts and relationships that are used to describe security issues. We further analyse and map these core concepts and relationships to five security standards (i.e., NIST SP 800-160, NIST SP 800-30 rev.1, NIST SP 800-27 rev.A, ISO/IEC 27001 and NISTIR 8053). As a contribution, this paper provides a set of core concepts and relationships that comply with the standards mentioned above and allow for a new security ontology to be developed.

It is known that offsets in general are not sustainable, i.e., if offsets in a system are modified it is not trivial to determine if this affects schedulability or not. In this paper we investigate if there are situations where offsets can be deemed sustainable, i.e., situations where one can safely modify an offset without impairing schedulability. We introduce, for the approximate Response-Time Analysis, a concept of a subsumes relation between demand bound functions and show that if offsets are modified in such a way that the modified demand bound function is subsumed by the original demand bound function, then the modification is sustainable. We show an example of how this information can be used in an engineering context where all system parameters are fixed but offsets. We generate all transaction that are subsumed by a schedulable transaction and merge this information in a presentable form for the engineer. This information can be used to safely modify the transaction or to investigate the robustness of the schedulability.

Modern collaborative and dynamic systems, such as System of Systems (SoS), can be considered as a set of interacting entities where the interactions are seen as the core activity fo rthese systems. The study of interactions is of importance inorder to discover emergent and inter dependent properties that impact the overall system’s behaviour. We introduce a role-based approach together with a taxonomy of roles for safety as a means to deal with emergent behaviours of high-collaborative systems that may impact the safety of the whole system. The aim ofour role-based approach is to discover the interactions that maybe harmful for the system and use them as starting point for common safety analysis techniques.

Today's systems are being built to connect to public or semi-public networks, are able to communicate with other systems, e.g., in the context of Internet-of-Things (IoT), involve multiple stakeholders, have dynamic system reconfigurations, and operate in increasingly unpredictable environments. In such complex systems, assuring safety and security in a continuous and joint effort is a major challenge, not the least due to the increasing number of attack surfaces arising from the increased connectivity. In this paper we present an approach that aims to bridge the gap between safety and security engineering. The potential of the approach is illustrated on the example of E-gas system, discussing the cases when unintentional faults as well as malicious attacks are taken into consideration when assuring safety of the described system. 

Preliminary hazard analysis (PHA) is a key safety-concerned activity, applied during the early stages of safety-critical systems development process, aiming to provide stakeholders with a general understanding of potential hazards. The identified hazards will be described and serve as a basis to further identify mitigation mechanisms in the subsequent development process. However, since various stakeholders will be involved in the identification process, a common understanding of the nature of hazards among stakeholders, such as what a hazard consists of and how to describe it without ambiguities, is of crucial importance to achieve the goal of PHA. In this work, we propose a hazard modeling language (HML) based on a hazard domain ontology, i.e., the Hazard Ontology, in order to facilitate the specification of identified hazards. In addition, we present an approach to the transformation from natural language hazard descriptions into the HML specification. Finally, an industrial PHA example is used to illustrate the usefulness of our work.

Safety requirements describe risk mitigations against failures that may cause catastrophic consequences on human life, environment and facilities. To be able to implement the correct risk mitigations, it is fundamental that safety requirements are de- fined based on the results issued from the safety analysis. In this paper, we introduce a heuristic approach to elicit safety requirements based on the knowledge about hazard’s causes, hazard’s sources and hazard’s consequences (i.e. hazard’s components) acquired during the safety analysis. The proposed approach is based on a Hazard Ontology that is used to structure the knowledge about the hazards identified during the safety analysis in order to make it available and accessible for requirements elicitation. We describe how this information can be used to elicit safety requirements, and provide a guidance to derive the safety requirements which are appropriate to deal with the hazards they mitigate.