The aging of the world's population, and consequently the need for controlled costs of medical and home care, introduce new scientific challenges that need to be addressed. In this context, the Ambient Assisted Living (AAL) constitutes a new approach, based on technological solutions, which arise to meet the demands of this public. Among the challenges of developing AAL systems are meeting ethical, legal (compliance), social, medical and technical constraints that must be gathered and consolidated in a specification of requirements. The specification of requirements is fundamental for the system to work according to the needs of the stakeholders and meet the restrictions to which it is submitted. These challenges and the need to formalize the specification of requirements for such systems has led the academic community to explore and establish new approaches for the development and verification of AAL systems and to integrate them into different areas of knowledge, such as ontology and compliance. In this context, this thesis aims, from the open standards of the Semantic Web, using the Descriptive Logic and the Ontology Web Language, to define an ontological approach to help the elicitation and specification of requirements (focusing on the non-functional, ethical and associated requirements compliance) in AAL systems. With this, a core ontology (Onto4CAAL) is presented to support the specification of requirements in AAL systems, where the elements that are part of this type of system are integrated. The research method used was a Systematic Literature Mapping, as well as a survey with specialists (academy and industry) in the domain. With the use of the core ontology, it was possible to develop a domain ontology (Onto4Elev) for Vertical Elevation Platforms, where a validation was carried out with the industry (another survey) in relation to the elements that constitute it and, subsequently, a scenario for simulation, extracting the requirements used and the legislation involved in this type of AAL system. As contributions of this thesis, we point out the use of logically formalized ontologies for the unambiguous and shared representation of the knowledge of requirements in AAL systems, making it possible to standardize the understanding of the terms associated with this type of system, the legislation involved and allowing to verify the relationships between the elements, helping the designer in making decisions.