Which of the following is essential for a well-structured data model?

A clear definition of classes and properties is fundamental for establishing a well-structured data model because it provides the framework necessary for organizing and managing data effectively within Pega. By clearly defining classes, developers can ensure that the data is logically categorized, which facilitates easier data management, retrieval, and manipulation.

Well-defined properties within these classes allow for accurate data representation and ensure that the data model meets the application's requirements. This clarity helps teams understand the structure of the application, promotes maintainability, and aids in implementing business logic effectively. When classes and properties are well-structured, it ultimately leads to enhanced performance and scalability of the application as it grows.

In contrast, while regular validation of property references, embedding UI controls, and limiting property references can contribute to a better data model, they do not directly address the foundational organization and clarity that a good data model requires. These aspects can be important for specific use cases or optimizations, but they rely on having a solid underlying definition of classes and properties.