## 5 Use Cases
### Route Assistant for Travelers with Special Needs
A notable feature of the described assistant related to the data is that the data are based on an ontology inspired by international standards for data models in the field of public transit [21] and [PERSON] [22], according to [PERSON] [23]. This ontology defines the concepts, relationships and semantic meaning of the context information, thus enabling interpretation of data in the public transit domain. Conceptually, this domain is divided into four subdomains:  
* _The actor domain_. All concepts related to intermodal transit network actors belong to this domain. The main actors are the travelers, transit operators and transit authorities, and the main actor functions are infrastructure, service and infrastructure provider, and service consumer. * _The infrastructure domain_. Concepts related to basic resources for the implementation of information services in a ubiquitous context belong to this domain (hardware resources, information service providers and client applications). These resources are: computing, communication, location and sensors. This is the most complex domain of the architecture because the concepts and functions envisaged in this area must ensure interoperability of all the information services. Physically, this domain is deployed in the components of the transit network. The transit company is responsible for this domain and the beneficiaries are the transit operators. * _The service provider domain_. Concepts related to different ubiquitous information services, such as payment systems, traveler assistants, and control operations, belong to this domain. The actors responsible for this domain are transit authorities and operators and the beneficiaries may be operating personnel, transit authority personnel and travelers. Specifications concerning technological and functional aspects belong to this domain. * _The information consumer domain_. All concepts related to the accessibility, utility and reliability of the ubiquitous client applications belong to this domain. It is therefore a high-level abstraction domain. The actors responsible for this domain are transit authorities and operators and the beneficiaries may be operating personnel, transit authority personnel and travelers. With regard to the accessibility and safety of a journey using public transit by highway, three critical differentiated phases exist in terms of objectives and data requirements: the boarding phase, the movement phase, and the disembarking phase. In each of these phases, the assistant operates as follows:  
1. _Passenger boarding phase_. The objective of the system is safe boarding, which occurs when a passenger boards the correct bus under conditions that do not endanger his or her physical safety that is, boarding when the bus is stopped and the access doors are open. This condition is achieved by indicating to the traveler that the vehicle that they selected is the correct vehicle via the data related to the route (PLI and VLI), current stop (VCS) and destination stop (PDS) and indicating when they can proceed to board, which will occur when the vehicle is stopped, using the vehicle speed data (VSL), and when the doors are open by the vehicle door status data (VDS). 2. _Passenger travel phase_. The objective of the system at this stage is to orient a passenger with special needs to provide safe and stress-free travel. The system communicates the last stop of the vehicle (VCS), the next stop (VNS) if the vehicle is stopped at a stop, the existing stop (VCS and VSL), and the number of remaining stops until his or her destination (VNS and VIS) is reached. 3. _Disembarking phase_. The objective of the system in this phase is safe disembarking. The system achieves this objective by alerting the traveler when he or she has reached his or her destination stop (PDS and VCS), that the vehicle has stopped (VVE), and that the exit doors are open (VDS).