The text discusses the critical role of semantic layers in ensuring data security and compliance in modern business environments. As businesses increasingly collect data, the need for secure access and control becomes paramount, necessitating tight security measures to prevent unauthorized data access and modification. A semantic layer acts as an abstraction between the user interface and the underlying database, providing functions beyond mere metrics definitions, such as data modeling, caching, and API layers, which enhance performance and maintain data accessibility. It incorporates data governance features, such as authentication tokens and role-based access control, to limit access to sensitive information, ensuring only authorized users can access or modify data. Moreover, a semantic layer supports multitenancy, allowing multiple organizations to use the same software instance while maintaining individualized data protection. By centralizing security contexts, semantic layers help organizations comply with regulations like HIPAA and SOC 2, providing granular control over data access and supporting audits and adjustments to access controls. The text underscores the importance of implementing data access controls upstream of data applications to enhance governance, ensure compliance, and protect sensitive information, exemplified through a fictional scenario that highlights the potential consequences of inadequate data security practices.