## 4 Semantically Defined Access Management Framework in Smart Cities  
The development of an access management framework is essential because previous work has identified the key requirement for security in smart cities as follows: it must be able to integrate and align across multiple domains, including built assets, existing digital services as well as actors themselves. These requirements align with the advantages provided by a semantic approach. As such, it has been possible to propose an access management framework that is semantically defined [23]. When it is necessary for the formal relationships established between the built environment and access management concepts to be modelled, it is recommended that the ontology and semantic modelling concepts are utilised. This entire approach is required since interoperability is a critical component of achieving holistic and accessible services in a smart city. Common problems include existing fragmented semantics across differing contexts that cause interoperability issues and create obstacles for software developers and integrators. Figure 1 provides an illustration of the process by which the core aspects of semantics required to facilitate digital twin access management are identified by the semantically defined cybersecurity framework, as well as how these disparate elements are combined to produce a unified semantic model. Figure 1: Semantically defined access management framework in smart cities. Thus, the justification for the creation of the framework will utilise semantic Web technologies to combine cyber security standards currently applied in various domains to model the physical items that comprise cities including processes, individuals and structures, as well as the digital services operating on them. Following the definition of the concept of the access management framework in smart cities, this section provides a definition of the access management ontology's specification which will deliver it for smart cities. The access management ontology for the built environment will be developed using the NeOn approach [24]. The initial process when applying the NeOn approach is the ontology requirement specification (ORS) [24]. This is required to determine the limits for the domain semantic modelling and emphasises the need to have access to suitable information. More specifically, it entails establishing the overarching aim of the ontology under development, the uses to which the ontology can be deployed, and the standards which need to be satisfied by the ontology [20]. The primary aim of the ontology is to identify the integrations that the access management framework requires with regards to formalised semantics. This provides integration with regards to innovative user interfaces, BIM datasets, digital twins, prevailing security standards, the available built environment services, cyber-physical systems, IoT devices, and physical built environment assets (see Figure 2). Therefore, digital twins will have an access management framework that feature formalised semantics to enable single sign-on (SSO) throughout all services relating to the built environment, ensure that all data remains secure and confidential, and apply access control. This is supported by digital twins' access management specifications. The last step involves identifying the criteria the ontology is required to satisfy. Applying the NeOn approach, this entails providing definitions for the competency questions. These questions help to determine how complex an ontology is by listing questions which should be capable of being answered using knowledge that is ontology-based [20; 24; 25; 26]. Five categories of competency questions were compiled (security standards, built environment services, actors, built environment data format, IoT devices) that reflect the aspects of access management being integrated by the model: objects, actions and individuals and the impact they have in terms of the efficiency of security efforts.